Abstract

RODRIGUEZ MENDOZA, Mario; H. MONTALDO, Hugo; BALCAZAR SANCHEZ, Juan Alberto  and  HERNANDEZ CERON, Joel. Serum progesterone levels in Pelibuey and Suffolk ewes under thermal stress. Vet. Méx [online]. 2009, vol.40, n.2, pp.197-202. ISSN 0301-5092.

In this study it was assessed the effect of high environmental temperature on the serum progesterone levels and whether this effect is smaller in sheep (Pelibuey) adapted to hot climate than in not adapted sheep (Suffolk). Thirty two ewes, 16 of the Pelibuey breed and 16 of the Suffolk breed, were synchronized with intravaginal sponges with FGA. At day two of the estrous cycle (day of estrus = day 0), the ewes were assigned to two treatments: a) Thermal stress group [n =16 (eight Pelibuey and eight Suffolk)]. From day two up to the return to estrus the ewes remained six hours a day in an environmental chamber at > 32°C (35 ± 1.4°C) and 31% of relative humidity (RH); b) control group [n = 16 (eight Pelibuey and eight Suffolk)], stayed at ambient temperature during all the study (19 ± 4°C and 31% of RH). Two blood samples were taken daily (at 9:00 am and 4:00 pm) from day 0 until the following estrus. Progesterone was measured by radioimmunoassay. Progesterone concentration data were analyzed using mixed linear models. The effects of the treatment, breed, time of measurement and interactions were tested. The random effect of the ewe nested in breed was added to the model to consider the repeated structure of the information. The length of the luteal phase and the estrous cycle was analyzed with a model that included the effects of the treatment, breed, and breed x treatment interaction. The length of the luteal phase (11.1 ± 0.15 versus 11.5 ± 0.15 days for thermal stress and control groups, respectively) and the estrous cycle (17.1 ± 0.24 versus 17.3 ± 0.3 days for thermal stress and control groups, respectively) was similar (P > 0.05) between groups. Progesterone concentrations were similar between treatments and there were no effects of the breed, neither treatment x breed interaction (P > 0.05). There is no evidence in this study that a high environmental temperature affects the serum progesterone levels in Pelibuey and Suffolk ewes.

Keywords : corpus luteum; thermal stress; sheep.

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