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vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Etymology_and_nomenclature"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Etymology and nomenclature</span> </div> </a> <ul id="toc-Etymology_and_nomenclature-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Four_phases" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Four_phases"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Four phases</span> </div> </a> <button aria-controls="toc-Four_phases-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Four phases subsection</span> </button> <ul id="toc-Four_phases-sublist" class="vector-toc-list"> <li id="toc-Proestrus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Proestrus"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Proestrus</span> </div> </a> <ul id="toc-Proestrus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Estrus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Estrus"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Estrus</span> </div> </a> <ul id="toc-Estrus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Metestrus_or_diestrus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Metestrus_or_diestrus"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Metestrus or diestrus</span> </div> </a> <ul id="toc-Metestrus_or_diestrus-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Anestrus" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Anestrus"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Anestrus</span> </div> </a> <ul id="toc-Anestrus-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Cycle-variability" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Cycle-variability"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Cycle-variability</span> </div> </a> <ul id="toc-Cycle-variability-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Frequency" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Frequency"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Frequency</span> </div> </a> <ul id="toc-Frequency-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Specific_species" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Specific_species"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Specific species</span> </div> </a> <button aria-controls="toc-Specific_species-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Specific species subsection</span> </button> <ul id="toc-Specific_species-sublist" class="vector-toc-list"> <li id="toc-Cats" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cats"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Cats</span> </div> </a> <ul id="toc-Cats-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Dogs" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Dogs"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>Dogs</span> </div> </a> <ul id="toc-Dogs-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Horses" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Horses"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.3</span> <span>Horses</span> </div> </a> <ul id="toc-Horses-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Rats" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rats"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.4</span> <span>Rats</span> </div> </a> <ul id="toc-Rats-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Bison" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Bison"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.5</span> <span>Bison</span> </div> </a> <ul id="toc-Bison-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Cattle" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cattle"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.6</span> <span>Cattle</span> </div> </a> <ul id="toc-Cattle-sublist" class="vector-toc-list"> <li id="toc-Estrous_control" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Estrous_control"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.6.1</span> <span>Estrous control</span> </div> </a> <ul id="toc-Estrous_control-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Others" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Others"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.7</span> <span>Others</span> </div> </a> <ul id="toc-Others-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Further reading</span> </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Estrous cycle</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 38 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-38" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">38 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AF%D9%88%D8%B1%D8%A9_%D9%88%D8%AF%D8%A7%D9%82%D9%8A%D8%A9" title="دورة وداقية – Arabic" lang="ar" hreflang="ar" data-title="دورة وداقية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%9F%D0%BE%D0%BB%D0%BE%D0%B2_%D1%86%D0%B8%D0%BA%D1%8A%D0%BB" title="Полов цикъл – Bulgarian" lang="bg" hreflang="bg" data-title="Полов цикъл" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Cicle_estral" title="Cicle estral – Catalan" lang="ca" hreflang="ca" data-title="Cicle estral" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Estr%C3%A1ln%C3%AD_cyklus" title="Estrální cyklus – Czech" lang="cs" hreflang="cs" data-title="Estrální cyklus" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Sexualzyklus" title="Sexualzyklus – German" lang="de" hreflang="de" data-title="Sexualzyklus" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Indlus" title="Indlus – Estonian" lang="et" hreflang="et" data-title="Indlus" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%9F%CE%B9%CF%83%CF%84%CF%81%CE%B9%CE%BA%CF%8C%CF%82_%CE%BA%CF%8D%CE%BA%CE%BB%CE%BF%CF%82" title="Οιστρικός κύκλος – Greek" lang="el" hreflang="el" data-title="Οιστρικός κύκλος" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Ciclo_estral" title="Ciclo estral – Spanish" lang="es" hreflang="es" data-title="Ciclo estral" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Oestro" title="Oestro – Esperanto" lang="eo" hreflang="eo" data-title="Oestro" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%AF%D9%88%D8%B1%D9%87_%D9%81%D8%AD%D9%84%DB%8C" title="دوره فحلی – Persian" lang="fa" hreflang="fa" data-title="دوره فحلی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/%C5%92strus" title="Œstrus – French" lang="fr" hreflang="fr" data-title="Œstrus" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/%C3%89astras" title="Éastras – Irish" lang="ga" hreflang="ga" data-title="Éastras" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EB%B0%9C%EC%A0%95_%EC%A3%BC%EA%B8%B0" title="발정 주기 – Korean" lang="ko" hreflang="ko" data-title="발정 주기" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%AE%E0%A4%A6_%E0%A4%9A%E0%A4%95%E0%A5%8D%E0%A4%B0" title="मद चक्र – Hindi" lang="hi" hreflang="hi" data-title="मद चक्र" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Siklus_estrus" title="Siklus estrus – Indonesian" lang="id" hreflang="id" data-title="Siklus estrus" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/Fengit%C3%ADmi" title="Fengitími – Icelandic" lang="is" hreflang="is" data-title="Fengitími" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Ciclo_estrale" title="Ciclo estrale – Italian" lang="it" hreflang="it" data-title="Ciclo estrale" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%99%D7%99%D7%97%D7%95%D7%9D" title="ייחום – Hebrew" lang="he" hreflang="he" data-title="ייחום" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-kn mw-list-item"><a href="https://kn.wikipedia.org/wiki/%E0%B2%AC%E0%B3%86%E0%B2%A6%E0%B3%86_%E0%B2%9A%E0%B2%95%E0%B3%8D%E0%B2%B0" title="ಬೆದೆ ಚಕ್ರ – Kannada" lang="kn" hreflang="kn" data-title="ಬೆದೆ ಚಕ್ರ" data-language-autonym="ಕನ್ನಡ" data-language-local-name="Kannada" class="interlanguage-link-target"><span>ಕನ್ನಡ</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%9B%E1%83%AB%E1%83%A3%E1%83%9C%E1%83%90%E1%83%9D%E1%83%91%E1%83%90" title="მძუნაობა – Georgian" lang="ka" hreflang="ka" data-title="მძუნაობა" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Ruja" title="Ruja – Lithuanian" lang="lt" hreflang="lt" data-title="Ruja" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Kitaran_estrus" title="Kitaran estrus – Malay" lang="ms" hreflang="ms" data-title="Kitaran estrus" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Brunst" title="Brunst – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Brunst" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/%C3%98strus" title="Østrus – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Østrus" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Ruja" title="Ruja – Polish" lang="pl" hreflang="pl" data-title="Ruja" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Ciclo_estral" title="Ciclo estral – Portuguese" lang="pt" hreflang="pt" data-title="Ciclo estral" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Ciclu_estral" title="Ciclu estral – Romanian" lang="ro" hreflang="ro" data-title="Ciclu estral" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%AD%D1%81%D1%82%D1%80%D1%83%D1%81" title="Эструс – Russian" lang="ru" hreflang="ru" data-title="Эструс" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Oestrous_cycle" title="Oestrous cycle – Simple English" lang="en-simple" hreflang="en-simple" data-title="Oestrous cycle" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Ruja" title="Ruja – Slovak" lang="sk" hreflang="sk" data-title="Ruja" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Kiima" title="Kiima – Finnish" lang="fi" hreflang="fi" data-title="Kiima" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/Paglalandi" title="Paglalandi – Tagalog" lang="tl" hreflang="tl" data-title="Paglalandi" data-language-autonym="Tagalog" data-language-local-name="Tagalog" class="interlanguage-link-target"><span>Tagalog</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%9A%E0%AE%BF%E0%AE%A9%E0%AF%88%E0%AE%AA%E0%AF%8D%E0%AE%AA%E0%AE%B0%E0%AF%81%E0%AE%B5%E0%AE%9A%E0%AF%8D_%E0%AE%9A%E0%AF%81%E0%AE%B4%E0%AE%B1%E0%AF%8D%E0%AE%9A%E0%AE%BF" title="சினைப்பருவச் சுழற்சி – Tamil" lang="ta" hreflang="ta" data-title="சினைப்பருவச் சுழற்சி" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/%C3%96strus" title="Östrus – Turkish" lang="tr" hreflang="tr" data-title="Östrus" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%95%D1%81%D1%82%D1%80%D1%83%D1%81" title="Еструс – Ukrainian" lang="uk" hreflang="uk" data-title="Еструс" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Chu_k%E1%BB%B3_%C4%91%E1%BB%99ng_d%E1%BB%A5c" title="Chu kỳ động dục – Vietnamese" lang="vi" hreflang="vi" data-title="Chu kỳ động dục" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E7%99%BC%E6%83%85%E6%9C%9F" title="發情期 – Cantonese" lang="yue" hreflang="yue" 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div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">For the biological genus name of the gadfly, see <a href="/wiki/Oestrus_(fly)" title="Oestrus (fly)">Oestrus (fly)</a>. For Satyr leader, see <a href="/wiki/Oestrus_(mythology)" title="Oestrus (mythology)">Oestrus (mythology)</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Lead_too_short plainlinks metadata ambox ambox-content ambox-lead_too_short" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Wiki_letter_w.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/en/thumb/6/6c/Wiki_letter_w.svg/40px-Wiki_letter_w.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/6/6c/Wiki_letter_w.svg/60px-Wiki_letter_w.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/6/6c/Wiki_letter_w.svg/80px-Wiki_letter_w.svg.png 2x" data-file-width="44" data-file-height="44" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article's <a href="/wiki/Wikipedia:Manual_of_Style/Lead_section#Length" title="Wikipedia:Manual of Style/Lead section">lead section</a> <b>may be too short to adequately <a href="/wiki/Wikipedia:Summary_style" title="Wikipedia:Summary style">summarize</a> the key points</b>.<span class="hide-when-compact"> Please consider expanding the lead to <a href="/wiki/Wikipedia:Manual_of_Style/Lead_section#Provide_an_accessible_overview" title="Wikipedia:Manual of Style/Lead section">provide an accessible overview</a> of all important aspects of the article.</span> <span class="date-container"><i>(<span class="date">March 2021</span>)</i></span></div></td></tr></tbody></table> <p>The <b>estrous cycle</b> (from <a href="/wiki/Latin_language" class="mw-redirect" title="Latin language">Latin</a> <i> <i lang="la"><a href="https://en.wiktionary.org/wiki/oestrus#Latin" class="extiw" title="wikt:oestrus">oestrus</a></i></i> 'frenzy', originally from <a href="/wiki/Ancient_Greek_language" class="mw-redirect" title="Ancient Greek language">Ancient Greek</a> <i> </i><span lang="grc"><a href="https://en.wiktionary.org/wiki/%CE%BF%E1%BC%B6%CF%83%CF%84%CF%81%CE%BF%CF%82#Ancient_Greek" class="extiw" title="wikt:οἶστρος">οἶστρος</a></span><i> (<span title="Ancient Greek transliteration" lang="grc-Latn"><i>oîstros</i></span>)</i> 'gadfly') is a set of recurring physiological changes induced by <a href="/wiki/Reproductive_hormone" class="mw-redirect" title="Reproductive hormone">reproductive hormones</a> in <a href="/wiki/Female" title="Female">females</a> of <a href="/wiki/Mammal" title="Mammal">mammalian</a> subclass <a href="/wiki/Theria" title="Theria">Theria</a>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Estrous cycles start after <a href="/wiki/Sexual_maturity" title="Sexual maturity">sexual maturity</a> in females and are interrupted by anestrous phases, otherwise known as "rest" phases, or by <a href="/wiki/Pregnancy_(mammals)" title="Pregnancy (mammals)">pregnancies</a>. Typically, estrous cycles repeat until death. These cycles are widely variable in duration and frequency depending on the species.<sup id="cite_ref-:3_2-0" class="reference"><a href="#cite_note-:3-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Some animals may display bloody vaginal discharge, often mistaken for <a href="/wiki/Menstruation_(mammal)" title="Menstruation (mammal)">menstruation</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity.<sup id="cite_ref-:22_4-0" class="reference"><a href="#cite_note-:22-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:12_5-0" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The male equivalent, seen primarily in ruminants, is called <a href="/wiki/Rut_(mammalian_reproduction)" title="Rut (mammalian reproduction)">rut</a>.<sup id="cite_ref-:3_2-1" class="reference"><a href="#cite_note-:3-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Differences_from_the_menstrual_cycle">Differences from the menstrual cycle</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=1" title="Edit section: Differences from the menstrual cycle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Menstrual_cycle#Cycles_and_phases" title="Menstrual cycle">Menstrual cycle § Cycles and phases</a></div> <p>Mammals share the same reproductive system, including the regulatory <a href="/wiki/Hypothalamus" title="Hypothalamus">hypothalamic</a> system that produces <a href="/wiki/Gonadotropin-releasing_hormone" title="Gonadotropin-releasing hormone">gonadotropin-releasing hormone</a> in pulses, the <a href="/wiki/Pituitary_gland" title="Pituitary gland">pituitary gland</a> that secretes <a href="/wiki/Follicle-stimulating_hormone" title="Follicle-stimulating hormone">follicle-stimulating hormone</a> and <a href="/wiki/Luteinizing_hormone" title="Luteinizing hormone">luteinizing hormone</a>, and the ovary itself that releases <a href="/wiki/Sex_hormone" title="Sex hormone">sex hormones</a>, including <a href="/wiki/Estrogen" title="Estrogen">estrogens</a> and <a href="/wiki/Progesterone" title="Progesterone">progesterone</a>. </p><p>However, animals that have estrous cycles <a href="/wiki/Resorption" title="Resorption">resorb</a> the <a href="/wiki/Endometrium" title="Endometrium">endometrium</a> if conception does not occur during that cycle. Mammals that have menstrual cycles shed the endometrium through <a href="/wiki/Menstruation_(mammal)" title="Menstruation (mammal)">menstruation</a> instead. </p><p>Humans, <a href="/wiki/Elephant_shrew" title="Elephant shrew">elephant shrews</a>, and a few other species have <a href="/wiki/Menstrual_cycle" title="Menstrual cycle">menstrual cycles</a> rather than estrous cycles. Humans, unlike most other species, have <a href="/wiki/Concealed_ovulation" title="Concealed ovulation">concealed ovulation</a>, a lack of obvious external signs to signal estral receptivity at <a href="/wiki/Ovulation" title="Ovulation">ovulation</a> (i.e., the ability to become pregnant). Some species of animals with estrous cycles have unmistakable outward displays of receptivity, ranging from engorged and colorful <a href="/wiki/Genitals" class="mw-redirect" title="Genitals">genitals</a> to behavioral changes like <a href="/wiki/Mating_call" title="Mating call">mating calls</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Etymology_and_nomenclature">Etymology and nomenclature</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=2" title="Edit section: Etymology and nomenclature"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><i>Estrus</i> is derived via Latin <i><span title="Latin-language text"><i lang="la">oestrus</i></span></i> ('<a href="/wiki/Rage_(emotion)" title="Rage (emotion)">frenzy</a>', '<a href="/wiki/Botfly" title="Botfly">gadfly</a>'), from Greek <span title="Ancient Greek (to 1453)-language text"><span lang="grc">οἶστρος</span></span> <i>oîstros</i> (literally 'gadfly', more figuratively 'frenzy', 'madness', among other meanings like 'breeze'). Specifically, this refers to the gadfly in <a href="/wiki/Ancient_Greek_mythology" class="mw-redirect" title="Ancient Greek mythology">Ancient Greek mythology</a> that <a href="/wiki/Hera" title="Hera">Hera</a> sent to torment <a href="/wiki/Io_(mythology)" title="Io (mythology)">Io</a>, who had been won in her <a href="/wiki/Cow" class="mw-redirect" title="Cow">heifer</a> form by <a href="/wiki/Zeus" title="Zeus">Zeus</a>.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (October 2021)">citation needed</span></a></i>]</sup> <a href="/wiki/Euripides" title="Euripides">Euripides</a> used <i>oestrus</i> to indicate 'frenzy', and to describe madness. <a href="/wiki/Homer" title="Homer">Homer</a> used the word to describe panic.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Plato" title="Plato">Plato</a> also used it to refer to an irrational drive<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> and to describe the <a href="/wiki/Soul" title="Soul">soul</a> "driven and drawn by the gadfly of desire".<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Somewhat more closely aligned to current meaning and usage of <i>estrus</i>, <a href="/wiki/Herodotus" title="Herodotus">Herodotus</a> (<i>Histories</i>, ch. 93.1) uses <i>oîstros</i> to describe the desire of fish to <a href="/wiki/Spawn_(biology)" class="mw-redirect" title="Spawn (biology)">spawn</a>.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p>The earliest use in English was with a meaning of 'frenzied passion'. In 1900, it was first used to describe '<a href="/wiki/Rut_(mammalian_reproduction)" title="Rut (mammalian reproduction)">rut</a> in animals; heat'.<sup id="cite_ref-Freeman_1994_10-0" class="reference"><a href="#cite_note-Freeman_1994-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p><p>In <a href="/wiki/British_English" title="British English">British English</a>, the spelling is <i>oestrus</i> or (rarely) <i>œstrus</i>. In all English spellings, the noun ends in <i>-us</i> and the adjective in <i>-ous</i>. Thus in <a href="/wiki/North_American_English" title="North American English">Modern International English</a>, a mammal may be described as "in estrus" when it is in that particular <a href="#Four_phases">part of the estrous-cycle</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Four_phases">Four phases</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=3" title="Edit section: Four phases"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">"Estrus" redirects here. For other uses, see <a href="/wiki/Estrus_(disambiguation)" class="mw-disambig" title="Estrus (disambiguation)">Estrus (disambiguation)</a>.</div> <p><span class="mw-default-size mw-valign-top" typeof="mw:File"><a href="/wiki/File:Estrous_cycle.png" class="mw-file-description" title="Overview of the mammalian estrous cycle"><img alt="Overview of the mammalian estrous cycle" src="//upload.wikimedia.org/wikipedia/commons/9/90/Estrous_cycle.png" decoding="async" width="819" height="185" class="mw-file-element" data-file-width="819" data-file-height="185" /></a></span> </p><p>A four-phase terminology is used in reference to animals with estrous cycles. </p> <div class="mw-heading mw-heading3"><h3 id="Proestrus">Proestrus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=4" title="Edit section: Proestrus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>One or several <a href="/wiki/Ovarian_follicle" title="Ovarian follicle">follicles</a> of the <a href="/wiki/Ovary" title="Ovary">ovary</a> start to grow. Their number is species-specific. Typically, this phase can last as little as one day or as long as three weeks, depending on the species. Under the influence of estrogen, the lining of the uterus (<a href="/wiki/Endometrium" title="Endometrium">endometrium</a>) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive; the old <a href="/wiki/Corpus_luteum" title="Corpus luteum">corpus luteum</a> degenerates; the uterus and the vagina distend and fill with fluid, become contractile and secrete a sanguinous fluid; the <a href="/wiki/Vaginal_epithelium" title="Vaginal epithelium">vaginal epithelium</a> proliferates and the vaginal cytology shows a large number of non-cornified nucleated epithelial cells. Variant terms for <i>proestrus</i> include <i>pro-oestrus</i>, <i>proestrum</i>, and <i>pro-oestrum</i>. </p> <div class="mw-heading mw-heading3"><h3 id="Estrus">Estrus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=5" title="Edit section: Estrus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><b>Estrus</b> or <b>oestrus</b> refers to the phase when the female is sexually receptive ("<b>in heat</b>" in American English, or "<b>on heat</b>" in British English). Under regulation by <a href="/wiki/Gonadotropin" title="Gonadotropin">gonadotropic hormones</a>, <a href="/wiki/Ovarian_follicle" title="Ovarian follicle">ovarian follicles</a> mature and estrogen secretions exert their biggest influence. The female then exhibits sexually receptive behavior,<sup id="cite_ref-Miller_et_al._12-0" class="reference"><a href="#cite_note-Miller_et_al.-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> a situation that may be signaled by visible physiologic changes. Estrus is commonly seen in the mammalian species, including some primates. </p><p>In some species, the <a href="/wiki/Vulva" title="Vulva">vulva</a> becomes swollen and reddened.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Ovulation" title="Ovulation">Ovulation</a> may occur spontaneously in others. Especially among <a href="/wiki/Quadrupeds" class="mw-redirect" title="Quadrupeds">quadrupeds</a>, a signal trait of estrus is the <a href="/wiki/Lordosis_behavior" title="Lordosis behavior">lordosis reflex</a>, in which the animal spontaneously elevates her hindquarters. </p><p><a href="/wiki/Controlled_internal_drug_release" title="Controlled internal drug release">Controlled internal drug release</a> devices are used in <a href="/wiki/Livestock" title="Livestock">livestock</a> for the synchronization of estrus. </p> <div class="mw-heading mw-heading3"><h3 id="Metestrus_or_diestrus">Metestrus or diestrus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=6" title="Edit section: Metestrus or diestrus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>This phase is characterized by the activity of the <a href="/wiki/Corpus_luteum" title="Corpus luteum">corpus luteum</a>, which produces progesterone. The signs of estrogen stimulation subside and the <a href="/wiki/Corpus_luteum" title="Corpus luteum">corpus luteum</a> starts to form. The <a href="/wiki/Uterus" title="Uterus">uterine</a> lining begins to appear. In the absence of <a href="/wiki/Pregnancy_(mammals)" title="Pregnancy (mammals)">pregnancy</a>, the diestrus phase (also termed <a href="/wiki/Pseudopregnancy" title="Pseudopregnancy">pseudopregnancy</a>) terminates with the <a href="/wiki/Regression_(medicine)" title="Regression (medicine)">regression</a> of the corpus luteum. The lining in the uterus is not shed, but is reorganized for the next cycle. Other spellings include <i>metoestrus</i>, <i>metestrum</i>, <i>metoestrum</i>, <i>dioestrus</i>, <i>diestrum</i>, and <i>dioestrum</i>. </p> <div class="mw-heading mw-heading3"><h3 id="Anestrus">Anestrus</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=7" title="Edit section: Anestrus"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the <a href="/wiki/Pineal_gland" title="Pineal gland">pineal gland</a> that releases <a href="/wiki/Melatonin" title="Melatonin">melatonin</a>. Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating the <a href="/wiki/Hypothalamus" title="Hypothalamus">hypothalamic</a> pulse activity of the <a href="/wiki/Gonadotropin-releasing_hormone" title="Gonadotropin-releasing hormone">gonadotropin-releasing hormone</a>. Anestrus is induced by time of year, <a href="/wiki/Pregnancy_(mammals)" title="Pregnancy (mammals)">pregnancy</a>, <a href="/wiki/Lactation" title="Lactation">lactation</a>, significant <a href="/wiki/Illness" class="mw-redirect" title="Illness">illness</a>, chronic energy deficit, and possibly age. Chronic exposure to anabolic steroids may also induce a persistent anestrus due to negative feedback on the hypothalamus/pituitary/gonadal axis. Other spellings include <i>anoestrus</i>, <i>anestrum</i>, and <i>anoestrum</i>. </p><p><span class="anchor" id="postpartum_estrus"></span> After completion (or abortion) of a pregnancy, some species have <i>postpartum estrus</i>, which is ovulation and corpus luteum production that occurs immediately following the birth of the young.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> For example, the <a href="/wiki/Mouse" title="Mouse">mouse</a> has a fertile postpartum estrus that occurs 14 to 24 hours following parturition. </p> <div class="mw-heading mw-heading2"><h2 id="Cycle-variability">Cycle-variability</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=8" title="Edit section: Cycle-variability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Estrous cycle variability differs among species, but cycles are typically more frequent in smaller animals. Even within species significant variability can be observed, thus <a href="/wiki/Cat" title="Cat">cats</a> may undergo an estrous cycle of 3 to 7 weeks.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> Domestication can affect estrous cycles due to changes in the environment. For most species, vaginal smear <a href="/wiki/Cell_biology" title="Cell biology">cytology</a> may be used in order to identify estrous cycle phases and durations.<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Frequency">Frequency</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=9" title="Edit section: Frequency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Some species, such as <a href="/wiki/Cat" title="Cat">cats</a>, <a href="/wiki/Cow" class="mw-redirect" title="Cow">cows</a> and <a href="/wiki/Domestic_pig" class="mw-redirect" title="Domestic pig">domestic pigs</a>, are <b>polyestrous</b>, meaning that they can go into heat several times per year. Seasonally polyestrous animals or <a href="/wiki/Seasonal_breeder" title="Seasonal breeder">seasonal breeders</a> have more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders: </p> <ul><li>Short-day breeders, such as <a href="/wiki/Sheep" title="Sheep">sheep</a>, <a href="/wiki/Goat" title="Goat">goats</a>, <a href="/wiki/Deer" title="Deer">deer</a> and <a href="/wiki/Red_Deer" class="mw-redirect" title="Red Deer">elk</a> are sexually active in fall or winter.</li> <li>Long-day breeders, such as <a href="/wiki/Horse" title="Horse">horses</a>, <a href="/wiki/Hamster" title="Hamster">hamsters</a> and <a href="/wiki/Ferret" title="Ferret">ferrets</a> are sexually active in spring and summer.</li></ul> <p>Species that go into heat twice per year are <b>diestrous</b>. Canines are diestrous.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="What species? Contradicts neighbouring claims. (September 2024)">citation needed</span></a></i>]</sup> </p><p><b>Monestrous</b> species, such as <a href="/wiki/Canidae" title="Canidae">canids</a><sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> and <a href="/wiki/Bear" title="Bear">bears</a>, have only one <a href="/wiki/Breeding_season" class="mw-redirect" title="Breeding season">breeding season</a> per year, typically in spring to allow growth of the <a href="/wiki/Offspring" title="Offspring">offspring</a> during the warm season to aid survival during the next winter. </p><p>A few mammalian species, such as <a href="/wiki/Rabbit" title="Rabbit">rabbits</a>, do not have an estrous cycle, instead being <a href="/wiki/Induced_ovulation_(animals)" title="Induced ovulation (animals)">induced to ovulate</a> by the act of mating and are able to conceive at almost any arbitrary moment. </p><p>Generally speaking, the timing of estrus is coordinated with seasonal availability of food and other circumstances such as migration, predation etc., the goal being to maximize the offspring's chances of survival. Some species are able to modify their estral timing in response to external conditions. </p> <div class="mw-heading mw-heading2"><h2 id="Specific_species">Specific species</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=10" title="Edit section: Specific species"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Cats">Cats</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=11" title="Edit section: Cats"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The female <a href="/wiki/Cat" title="Cat">cat</a> in heat has an estrus of 14 to 21 days and is generally characterized as an <a href="/wiki/Induced_ovulator" class="mw-redirect" title="Induced ovulator">induced ovulator</a>, since coitus induces ovulation. However, various incidents of spontaneous ovulation have been documented in the domestic cat and various non-domestic species.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> Without ovulation, she may enter interestrus, which is the combined stages of diestrus and anestrus, before reentering estrus. With the induction of ovulation, the female becomes pregnant or undergoes a non-pregnant <a href="/wiki/Luteal_phase" title="Luteal phase">luteal phase</a>, also known as <a href="/wiki/Pseudopregnancy" title="Pseudopregnancy">pseudopregnancy</a>. Cats are polyestrous but experience a seasonal anestrus in autumn and late winter.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Dogs">Dogs</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=12" title="Edit section: Dogs"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Canine_reproduction" title="Canine reproduction">Canine reproduction</a></div> <p>A female <a href="/wiki/Dog" title="Dog">dog</a> is usually diestrous (goes into heat typically twice per year), although some breeds typically have one or three cycles per year. The proestrus is relatively long at 5 to 9 days, while the estrus may last 4 to 13 days, with a diestrus of 60 days followed by about 90 to 150 days of anestrus. Female dogs bleed during estrus, which usually lasts from 7–13 days, depending on the size and maturity of the dog. Ovulation occurs 24–48 hours after the luteinizing hormone peak, which occurs around the fourth day of estrus; therefore, this is the best time to begin breeding. Proestrus bleeding in dogs is common and is believed to be caused by <a href="/wiki/Leukocyte_extravasation" title="Leukocyte extravasation">diapedesis</a> of <a href="/wiki/Red_blood_cell" title="Red blood cell">red blood cells</a> from the blood vessels due to the increase of the <a href="/wiki/Estradiol" title="Estradiol">estradiol-17β hormone</a>.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Horses">Horses</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=13" title="Edit section: Horses"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Horse_reproduction" class="mw-redirect" title="Horse reproduction">Horse reproduction</a></div> <p>A <a href="/wiki/Mare_(horse)" class="mw-redirect" title="Mare (horse)">mare</a> may be in heat for 4 to 10 days, followed by approximately 14 days in diestrus. Thus, a cycle may be short, totaling approximately 3 weeks.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> Horses mate in spring and summer; autumn is a transition time, and anestrus occurs during winter. </p><p>A feature of the <a href="/wiki/Fertility" title="Fertility">fertility</a> cycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down", become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones that activate the breeding cycle to be released. As it happens, this benefits these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky. </p> <div class="mw-heading mw-heading3"><h3 id="Rats">Rats</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=14" title="Edit section: Rats"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Rats are polyestrous animals that typically have rapid cycle lengths of 4 to 5 days.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> Although they ovulate spontaneously, they do not develop a fully functioning corpus luteum unless they receive coital stimulation. Fertile mating leads to pregnancy in this way, but infertile mating leads to a state of pseudopregnancy lasting about 10 days. Mice and hamsters have similar behavior.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> The events of the cycle are strongly influenced by lighting periodicity.<sup id="cite_ref-Freeman_1994_10-1" class="reference"><a href="#cite_note-Freeman_1994-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>A set of follicles starts to develop near the end of proestrus and grows at a nearly constant rate until the beginning of the subsequent estrus when the growth rates accelerate eightfold. Ovulation occurs about 109 hours after the start of follicle growth. </p><p><a href="/wiki/Estrogen" title="Estrogen">Estrogen</a> peaks at about 11 am on the day of proestrus. Between then and midnight there is a surge in <a href="/wiki/Progesterone" title="Progesterone">progesterone</a>, <a href="/wiki/Luteinizing_hormone" title="Luteinizing hormone">luteinizing hormone</a> and <a href="/wiki/Follicle-stimulating_hormone" title="Follicle-stimulating hormone">follicle-stimulating hormone</a>, and ovulation occurs at about 4 am on the next estrus day. The following day, metestrus, is called early diestrus or diestrus I. During this day, the <a href="/wiki/Corpus_luteum" title="Corpus luteum">corpora lutea</a> grow to a maximal volume, achieved within 24 hours of ovulation. They remain at that size for three days, halve in size before the metestrus of the next cycle and then shrink abruptly before estrus of the cycle after that. Thus the ovaries of cycling rats contain three different sets of corpora lutea at different phases of development.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Bison">Bison</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=15" title="Edit section: Bison"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Buffalo have an estrous cycle of about 22 to 24 days. Buffalo are known for difficult estrus detection. This is one major reason for being less productive than <a href="/wiki/Cattle" title="Cattle">cattle</a>. During four phases of its estrous cycle, mean weight of <a href="/wiki/Corpus_luteum" title="Corpus luteum">corpus luteum</a> has been found to be 1.23±0.22g (metestrus), 3.15±0.10g (early diestrus), 2.25±0.32g (late diestrus), and 1.89±0.31g (proestrus/estrus), respectively. The plasma progesterone concentration was 1.68±0.37, 4.29±0.22, 3.89±0.33, and 0.34±0.14 ng/ml while mean vascular density (mean number of vessels/10 microscopic fields at 400x) in corpus luteum was 6.33±0.99, 18.00±0.86, 11.50±0.76, and 2.83±0.60 during the metestrus, early diestrus, late diestrus and proestrus/estrus, respectively.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Cattle">Cattle</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=16" title="Edit section: Cattle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Female cattle, also referred to as "<a href="/wiki/Heifer_(cow)" class="mw-redirect" title="Heifer (cow)">heifers</a>" in agriculture, will gradually enter standing estrus, or "standing heat," starting at puberty between 9 and 15 months of age. The cow estrous cycle typically lasts 21 days.<sup id="cite_ref-:12_5-1" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Standing estrus is a visual cue which signifies sexual receptivity for <a href="/wiki/Copulation_(zoology)" title="Copulation (zoology)">mounting</a> by male cattle. This behavior lasts anywhere between 8 and 30 hours at a time.<sup id="cite_ref-:0_26-0" class="reference"><a href="#cite_note-:0-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> Other behaviors of the female during standing estrus may change, including, but not limited to: nervousness, swollen <a href="/wiki/Vulva" title="Vulva">vulva</a>, or attempting to mount other animals.<sup id="cite_ref-:0_26-1" class="reference"><a href="#cite_note-:0-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> While visual and behavioral cues are helpful to the male cattle, estrous stages cannot be determined by the human eye. Rather, the stage can be estimated from the appearance of the corpora lutea or follicle composition.<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Estrous_control">Estrous control</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=17" title="Edit section: Estrous control"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Estrous_synchronization" title="Estrous synchronization">Estrous synchronization</a></div> <p>Due to the widespread use of bovine animals in agriculture, cattle estrous cycles have been widely studied, and manipulated, in an effort to maximize profitability through reproductive management.<sup id="cite_ref-:0_26-2" class="reference"><a href="#cite_note-:0-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> Much estrous control in cattle is for the purpose of synchronization, a practice or set of practices most often used by cattle farmers to control the timing and duration of estrus in large herds.<sup id="cite_ref-:22_4-1" class="reference"><a href="#cite_note-:22-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget.<sup id="cite_ref-:22_4-2" class="reference"><a href="#cite_note-:22-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Some of the <a href="/wiki/Food_and_Drug_Administration" title="Food and Drug Administration">FDA</a>-approved drugs and devices used to mimic natural hormones of the estrous cycle include, but are not limited to, the following classes: </p> <ul><li><a href="/wiki/Gonadorelin" title="Gonadorelin">Gonadorelin</a>: There are currently five available gonadorelin products that are FDA-Approved.<sup id="cite_ref-:4_29-0" class="reference"><a href="#cite_note-:4-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> Usually, gonadorelin is used in conjunction with another estrous control drug (typically, prostaglandin).<sup id="cite_ref-:4_29-1" class="reference"><a href="#cite_note-:4-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:5_30-0" class="reference"><a href="#cite_note-:5-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> This drug is used to mimic gonadotropin releasing hormone (GnRH) and may also be used to treat ovarian cysts.<sup id="cite_ref-:12_5-2" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Prostaglandin" title="Prostaglandin">Prostaglandin</a>: Mimics the prostaglandin F2-alpha hormone released when no pregnancy has occurred and regresses the corpus luteum.<sup id="cite_ref-:12_5-3" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> This drug is used to achieve more consistent results in artificial insemination.<sup id="cite_ref-:5_30-1" class="reference"><a href="#cite_note-:5-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/Progestin" class="mw-redirect" title="Progestin">Progestin</a>: Used to suppress estrus and/or block ovulation.<sup id="cite_ref-:12_5-4" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Most commonly, it is administered via an intravaginal insert comparable to an <a href="/wiki/Intrauterine_device" title="Intrauterine device">IUD</a>, which used in controlling menstrual periods.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> It is also available as a medicated feed, but this method is not yet approved for cattle crop synchronization.<sup id="cite_ref-:12_5-5" class="reference"><a href="#cite_note-:12-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></li></ul> <p>There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget.<sup id="cite_ref-:22_4-3" class="reference"><a href="#cite_note-:22-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>Bovine estrous cycles may also be impacted by other bodily functions such as <a href="/wiki/Oxytocin" title="Oxytocin">oxytocin</a> levels.<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> Additionally, <a href="/wiki/Hyperthermia" title="Hyperthermia">heat stress</a> has been linked to impairment of follicular development, especially impactful to the first-wave dominant follicle.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> Future synchronization programs are planning to focus on the impact of heat stress on fertilization and embryonic death rates after <a href="/wiki/Artificial_insemination" title="Artificial insemination">artificial insemination</a>.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> </p><p>Additionally, work has been done regarding other mammalian females, such as in dogs, for estrous control; However, there are yet to be any approved medications outside of those commercially available.<sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Others">Others</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=18" title="Edit section: Others"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Estrus frequencies of some other notable mammals: </p> <ul><li><a href="/wiki/Sheep" title="Sheep">Sheep</a>: 18 days</li> <li><a href="/wiki/Pig" title="Pig">Pig</a>: 21 days</li> <li><a href="/wiki/Goat" title="Goat">Goat</a>: 21 days</li> <li><a href="/wiki/Donkey" title="Donkey">Donkey</a>: 13 to 31 days (average 23)</li> <li><a href="/wiki/Elephant" title="Elephant">Elephant</a>: 16 weeks</li> <li><a href="/wiki/Wolf" title="Wolf">Wolf</a>: 9 days</li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=19" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Mating_system" title="Mating system">Mating system</a></li> <li><a href="/wiki/Musth" title="Musth">Musth</a></li> <li><a href="/wiki/Neutering" title="Neutering">Neutering</a></li> <li><a href="/wiki/Progesterone-releasing_intravaginal_device" class="mw-redirect" title="Progesterone-releasing intravaginal device">Progesterone-releasing intravaginal device</a></li> <li><a href="/wiki/Reproductive_cycle" class="mw-redirect" title="Reproductive cycle">Reproductive cycle</a></li> <li><a href="/wiki/Rut_(mammalian_reproduction)" title="Rut (mammalian reproduction)">Rut (mammalian reproduction)</a></li> <li><a href="/wiki/Sexual_swelling" title="Sexual swelling">Sexual swelling</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=20" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">Hill, M. A. (2021, April 6) Embryology <i>Estrous Cycle</i>. Retrieved from <a rel="nofollow" class="external free" href="https://embryology.med.unsw.edu.au/embryology/index.php/Estrous_Cycle">https://embryology.med.unsw.edu.au/embryology/index.php/Estrous_Cycle</a></span> </li> <li id="cite_note-:3-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-:3_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:3_2-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">Bronson, F. H., 1989. Mammalian Reproductive Biology. University of Chicago Press, Chicago, IL, USA.</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFLleraYuill2021" class="citation web cs1">Llera, Ryan; Yuill, Cheryl (2021). <a rel="nofollow" class="external text" href="https://vcahospitals.com/know-your-pet/estrus-cycles-in-dogs">"Estrous Cycles in Dogs"</a>. <i>VCA Hospitals</i><span class="reference-accessdate">. Retrieved <span class="nowrap">April 6,</span> 2021</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=VCA+Hospitals&rft.atitle=Estrous+Cycles+in+Dogs&rft.date=2021&rft.aulast=Llera&rft.aufirst=Ryan&rft.au=Yuill%2C+Cheryl&rft_id=https%3A%2F%2Fvcahospitals.com%2Fknow-your-pet%2Festrus-cycles-in-dogs&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEstrous+cycle" class="Z3988"></span></span> </li> <li id="cite_note-:22-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-:22_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:22_4-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-:22_4-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-:22_4-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://agrilifeextension.tamu.edu/library/ranching/synchronizing-estrus-in-cattle/">"Synchronizing Estrus in Cattle - How does estrus synchronization work?"</a>. <i>Texas A&M AgriLife Extension Service</i><span class="reference-accessdate">. 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(1999). <a rel="nofollow" class="external text" href="https://doi.org/10.1095%2Fbiolreprod61.1.188">"Circannual variations in intraovarian oocyte but not epididymal sperm quality in the domestic cat"</a>. <i>Biology of Reproduction</i>. <b>61</b> (1): 188–194. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1095%2Fbiolreprod61.1.188">10.1095/biolreprod61.1.188</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/10377048">10377048</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Biology+of+Reproduction&rft.atitle=Circannual+variations+in+intraovarian+oocyte+but+not+epididymal+sperm+quality+in+the+domestic+cat&rft.volume=61&rft.issue=1&rft.pages=188-194&rft.date=1999&rft_id=info%3Adoi%2F10.1095%2Fbiolreprod61.1.188&rft_id=info%3Apmid%2F10377048&rft.aulast=Spindler&rft.aufirst=R.+E.&rft.au=Wildt%2C+D.+E.&rft_id=https%3A%2F%2Fdoi.org%2F10.1095%252Fbiolreprod61.1.188&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEstrous+cycle" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPelicanWildtPukazhenthiHoward2006" class="citation journal cs1">Pelican, K.; Wildt, D.; Pukazhenthi, B.; Howard, J. G. (2006). "Ovarian control for assisted reproduction in the domestic cat and wild felids". <i>Theriogenology</i>. <b>66</b> (1): 37–48. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1016%2Fj.theriogenology.2006.03.013">10.1016/j.theriogenology.2006.03.013</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/16630653">16630653</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Theriogenology&rft.atitle=Ovarian+control+for+assisted+reproduction+in+the+domestic+cat+and+wild+felids&rft.volume=66&rft.issue=1&rft.pages=37-48&rft.date=2006&rft_id=info%3Adoi%2F10.1016%2Fj.theriogenology.2006.03.013&rft_id=info%3Apmid%2F16630653&rft.aulast=Pelican&rft.aufirst=K.&rft.au=Wildt%2C+D.&rft.au=Pukazhenthi%2C+B.&rft.au=Howard%2C+J.+G.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEstrous+cycle" class="Z3988"></span></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Estrous_cycle&action=edit&section=22" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20090309174640/http://www.siu.edu/~tw3a/431estcy.htm">Systematic overview</a></li> <li><a rel="nofollow" class="external text" href="http://www.etymonline.com/index.php?term=estrus">Etymology</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20050801074824/http://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/filne_e.htm">Cat estrous cycle</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20050419100147/http://maine.maine.edu/~rcausey/estrous.HTM">Horse estrous cycle</a></li> <li><a rel="nofollow" class="external text" href="https://pethomeguide.com/dogsinheat/">Dogs in Heat - FAQ</a></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSkloot2007" class="citation news cs1">Skloot, Rebecca (December 9, 2007). <a rel="nofollow" class="external text" href="https://www.nytimes.com/2007/12/09/magazine/09lapdance.html?ref=magazine">"Lap-dance Science"</a>. <i>The New York Times Magazine</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+New+York+Times+Magazine&rft.atitle=Lap-dance+Science&rft.date=2007-12-09&rft.aulast=Skloot&rft.aufirst=Rebecca&rft_id=https%3A%2F%2Fwww.nytimes.com%2F2007%2F12%2F09%2Fmagazine%2F09lapdance.html%3Fref%3Dmagazine&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEstrous+cycle" class="Z3988"></span></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline 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