Resumen

CASTILLO-MALDONADO, P.P. et al. Resumption of postpartum reproductive activity in hairy sheep. Arch. zootec. [online]. 2013, vol.62, n.239, pp.419-428. ISSN 1885-4494.  https://dx.doi.org/10.4321/S0004-05922013000300010.

The purpose of this study was to determine the effect of suckling, postpartum (PP) synchronization protocol and the ram effect on reproductive performance of hairy sheep. Isolated from the rams, 96 ewes were randomly assigned to one of two groups at lambing (n=48): continuous suckling for 18 h (Ac) and controlled suckling for 30 minutes twice a day (Lc). On day 35 PP, both groups were synchronized with CIDR (Controlled Internal Drug Release) for 10 days, 48 hours before CIDR removal, 7,5 mg of dinoprost was administered and the effect of the ram (Ca) 48 hours before and at the time of CIDR removal were tested. We determined progesterone (P₄) por radioimmunoassay at 30, 35, 50, 55 y 64 days PP. The ewes were inseminated intrauterine by abdominal laparoscopy 12 to 15 hours after estrus onset. The response variables were: percentage of ovulation before 35 days PP, time of estrus onset, pregnancy rate, prolificacy, fecundity and live weight of the ewes and their lambs. The information obtained was analyzed using logistic regression and Poisson, chi-square test, survival curves and repeated measures analysis. The percentage of ewes that ovulated before 35 days PP was higher (p<0.05) in Lc (89.6 %) than Ac (52.1 %). The weight of the ewes was similar (p>0.05) between treatments. The weight of lambs was higher (p<0.05) in Ac after 41 days PP and there was no mortality during lactation. After CIDR removal all ewes showed estrus, being those of Lc (p<0.05) the first to manifest estrous behavior (50 hours). Pregnancy rate, prolificacy and fecundity were not different between treatments and averaged 82.3, 1.84 and 1.51 %, respectively. The results indicate that controlling lactation increases and concentrates the number of ewes that ovulated before 35 days PP. All ewes responded to the synchronization postpartum and the ram effect showing estrous behavior and only one ewe presented corpora lutea of shortened lifespan.

Palabras clave : CIDR; Controlled lactation; Induction of oestrous; Male effect; Progesterone; Ram effect; Suckling.

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