Reproductive performance of Merino-rambouillet prepubertal ewes under highland sub-tropical conditions II. male stimulation of seasonal anestrous

Maritinez, G.; Urrutia, J., Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias ;Martinez, L.;Meza- Herrera, C.A.

Reproductive performance of Merino-rambouillet prepubertal ewes under highland sub-tropical conditions II. male stimulation of seasonal anestrous

2005

Maritinez, G. | Urrutia, J., Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias (Mexico));Martinez, L.(Universidad Autonoma del Estado de Mexico, Fucultad de Medicina Veterinaria y Zootecnia (Mexico));Meza- Herrera, C.A.(Universidad Autonoma Chapingo, Unidad Regional Universitaria de zonas Aridas (Mexico))

To examine the response of the male stimulus upon the out-of-season (February to June) ovarian activity of prepubertal Merino Rambouillet ewes under highland sub-tropical conditions, (19° NL), a total of 155 ewes (35.3+3.7 kg, 2.4±0.5 body condition score, 22 mo) were randomly assigned to one of eight experimental breeding periods (EBP). The ram introduction dates were February 5th, February 23rd, March 12th, March 30th, April 16th, May 4th, May 21st, and June 8th. Serum progesterone (P4) concentrations were quantified by RIA from samples collected every three days during a period of 17 d prior to and 17 d after ram exposure. A total of 16 ewes depicted ovulatory activity prior to ram exposure. On average, 63 of the male exposed ewes depicted ovulatory response during the whole experimental period. Ewes from the EBP of April 16th, May 4th, May 21st and June 8th, besides an increased response to the male stimulus (53, 90, 79 and 85), also depicted the largest fertility rates with corresponding percentage values of 40, 78, 67 and 82. Improving the reproductive efficiency by scheduling earlier breeding programs by means of the ram effect could be of economic significance.

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