Resumo

TRUJILLO-QUIROGA, María J.; GALLEGOS-SANCHEZ, Jaime; PORRAS-ALMERAYA, Antonio  e  VALENCIA-MENDEZ, Javier. Artificial long days induce anoestrus in pelibuey ewes with continuous reproductive activity. Agrociencia [online]. 2007, vol.41, n.5, pp.513-519. ISSN 2521-9766.

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 (χ2) 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>0.05). Anoestrus occurred in 60% of the females in the continuous group and 66.6% in the seasonal group (p>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.

Palavras-chave : Continuous reproductive activity; artificial photoperiod; photosensitivity; reproductive seasonality.

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