<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>1405-3195</journal-id>
<journal-title><![CDATA[Agrociencia]]></journal-title>
<abbrev-journal-title><![CDATA[Agrociencia]]></abbrev-journal-title>
<issn>1405-3195</issn>
<publisher>
<publisher-name><![CDATA[Colegio de Postgraduados]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S1405-31952007000500513</article-id>
<title-group>
<article-title xml:lang="es"><![CDATA[Los días artificiales largos inducen el anestro en ovejas pelibuey con patrón reproductivo continuo]]></article-title>
<article-title xml:lang="en"><![CDATA[Artificial long days induce anoestrus in pelibuey ewes with continuous reproductive activity]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Trujillo-Quiroga]]></surname>
<given-names><![CDATA[María J.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Gallegos-Sánchez]]></surname>
<given-names><![CDATA[Jaime]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Porras-Almeraya]]></surname>
<given-names><![CDATA[Antonio]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Valencia-Méndez]]></surname>
<given-names><![CDATA[Javier]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Universidad Nacional Autónoma de México Facultad de Medicina Veterinaria y Zootecnia ]]></institution>
<addr-line><![CDATA[ D. F.]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,Colegio de Posgraduados Campus Montecillo ]]></institution>
<addr-line><![CDATA[Montecillo Estado de México]]></addr-line>
<country>Mexico</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>08</month>
<year>2007</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>08</month>
<year>2007</year>
</pub-date>
<volume>41</volume>
<numero>5</numero>
<fpage>513</fpage>
<lpage>519</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S1405-31952007000500513&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S1405-31952007000500513&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S1405-31952007000500513&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen: Las ovejas originarias de latitudes tropicales, como la Pelibuey, pueden ovular continuamente, pero se desconoce si esa actividad continúa a mayores latitudes. Ovejas Pelibuey continuas (grupo 1, n=15) y estacionales (grupo 2, n=15) fueron expuestas durante 90 d (21 de diciembre de 2002 al 21 de marzo de 2003) a un fotoperiodo inhibitorio (16hL/8hO), similar al de latitudes altas (56°), utilizando una cámara de luz controlada. La actividad ovárica se evaluó mediante la concentración plasmática de progesterona en muestras tomadas dos veces por semana, desde una semana antes de la aplicación del fotoperiodo hasta dos meses después de concluir el tratamiento. Se comparó el número de días con actividad ovulatoria (prueba de t) y el porcentaje de hembras con actividad ovulatoria (&#967;2) entre ambos grupos. Las ovejas mantuvieron su actividad durante 75.5+11.8 y 73.3+13.6 d para los grupos continuas y estacionales (p&gt;0.05). Hubo anestro en 60% del grupo continuo y 66.6% del grupo estacional (p&gt;0.05). Se concluye que las ovejas Pelibuey seleccionadas como continuas no son sensibles a los cambios del fotoperiodo en una latitud de 19° N. Sin embargo, al exponerlas a un fotoperiodo más amplio, activan el mecanismo neuroendocrino que controla el anestro estacional.]]></p></abstract>
<abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract: Sheep from the tropical latitudes such as Pelibuey, can ovulate continuously, but it is unknown whether this activity continues at higher latitudes. Continuous Pelibuey sheep (group 1, n=15) and seasonal (group 2, n=15) were exposed to an inhibitory photoperiod (16 h L/8 h D), similar to high latitudes (56°) for 90 days (December 21 2002 to March 21 2003), using a controlled light chamber. Ovarian activity was evaluated with plasmatic progesterone concentration in samples taken twice a week, beginning one week before application of the photoperiod up to two months after concluding the treatment. The number of days of ovulatory activity (t test) and the percentage of females with ovulatory activity (&#967;2) of the two groups were compared. The ewes of the continuous group maintained their activity for 75.5+11.8 d and the seasonal group for 73.3+13.6 d (p&gt;0.05). Anoestrus occurred in 60% of the females in the continuous group and 66.6% in the seasonal group (p&gt;0.05). It is concluded that Pelibuey ewes selected as continuous are not sensitive to changes in photoperiod at 19° N latitude. However, exposing them to a longer photoperiod activates the neuroendocrine mechanism that controls seasonal anoestrus.]]></p></abstract>
<kwd-group>
<kwd lng="es"><![CDATA[Actividad reproductiva continua]]></kwd>
<kwd lng="es"><![CDATA[fotoperiodo artificial]]></kwd>
<kwd lng="es"><![CDATA[fotosensibilidad]]></kwd>
<kwd lng="es"><![CDATA[ovejas Pelibuey]]></kwd>
<kwd lng="es"><![CDATA[estacionalidad reproductiva]]></kwd>
<kwd lng="en"><![CDATA[Continuous reproductive activity]]></kwd>
<kwd lng="en"><![CDATA[artificial photoperiod]]></kwd>
<kwd lng="en"><![CDATA[photosensitivity]]></kwd>
<kwd lng="en"><![CDATA[reproductive seasonality]]></kwd>
</kwd-group>
</article-meta>
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