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Stimulation of estrous behavior in grazing female goats by continuous or discontinuous exposure to males^1,2

R. Rivas-Muñoz^*, G. Fitz-Rodríguez^*, P. Poindron, B. Malpaux and J. A. Delgadillo^*,3

^* Centro de Investigación en Reproducción Caprina, Universidad Autónoma Agraria Antonio Narro, Periférico Raúl López Sánchez y Carretera a Santa Fe, C.P. 27054, Torreón, Coahuila, México; and and Physiologie de la Reproduction et des Comportements, UMR 6175 INRA-CNRS-Université de Tours-Haras Nationaux, IFR 135, 37380 Nouzilly, France

³ Corresponding author: joaldesa{at}yahoo.com

Two experiments were conducted during the anestrous period to determine: (1) whether males rendered sexually active by exposure to artificial long days stimulate estrous activity of female goats under grazed conditions (Exp. 1); and (2) whether continuous presence of the buck is necessary to stimulate this estrous activity (Exp. 2). In Exp. 1, 2 groups of females (n = 20/group), one in confinement and another under grazing conditions, were exposed to 4 bucks subjected to natural photoperiod (2 males/group). Two other groups of females (n = 20/group), in confinement or grazing, were exposed to 4 males treated with artificial long days (2 males/group). All groups were exposed to males for 15 d. The percentage of does detected in estrus during these 15 d was greater (P < 0.001) in the 2 groups exposed to males sexually prepared by long days (confined, 95%; grazed, 90%) than in groups exposed to males in natural photoperiod (confined, 15%; grazed, 45%). Does in Exp. 2 were allowed to graze and were exposed continuously (n = 26) or discontinuously (from 1700 to 0900; n = 26) for 18 d to males that had been stimulated to enter the breeding season by exposure to long days. The proportion of does that displayed estrous behavior in 18 d did not differ (P = 0.55) between groups (96.2 and 92.3% for continuous and discontinuous groups, respectively). The results indicate that anestrous goats managed under grazing conditions can be stimulated to express estrus by joining with males previously exposed to artificial long days. Continuous presence of the male is not necessary for this male effect.

Key Words: anestrous female • estrous activity • male effect • management system • photoperiod

² The authors are grateful to Rogelio Muñoz and Gonzalo Zárate for providing the female goats necessary for these studies; to Dolores López for her excellent and kind secretarial assistance. Raymundo Rivas-Muñoz (grateful to Instituto Tecnológico de Torreón-DGEST) and Gonzalo Fitz-Rodríguez were supported by a CONACyT scholarship during their doctoral studies.