REGULAR ARTICLES Estrus induction in anestrous mixed-breed goats using the “female-to-female effect” Rafael Rodríguez-Martínez & Oscar Ángel-García & Juan Manuel Guillén-Muñoz & Pedro Antonio Robles-Trillo & Maria de los Angeles De Santiago-Miramontes & Cesar Alberto Meza-Herrera & Miguel Mellado & Francisco Gerardo Véliz Accepted: 25 October 2012 # Springer Science+Business Media Dordrecht 2012 Abstract A trial was conducted during the anestrous period in female goats to determine: (a) whether estrus can be in- duced in anestrous goats by administration of equine chorion- ic gonadotropic hormone (eCG) and PGF 2α under pen conditions and (b) whether these sexually active female goats can elicit sexual arousal in sexually inactive bucks. One hundred and fifteen pluriparous, nonlactating mixed-breed female goats were randomly assigned to one of four treatment groups: (1) administration of a single dose of 240 IU of eCG, 50 μg PGF 2α i.m., and 25 mg progesterone (P 4 ) (eCG; n 0 30); (2) administration of P 4 and exposure to female goats treated with eCG–PGF 2α (P 4 ; n 0 39); (3) administration of 0.5 ml saline and P 4 (Sal; n 0 23); and (4) P 4 plus exposure to female goats treated with saline (Con; n 0 23). After hormone administration, all goats were put together with adult sexually inactive bucks for 15 days. The percentage of goats in estrus during these 15 days was similar in eCG-treated animals and untreated animals exposed to the eCG animals (97 and 95 %). Pregnancy rate was also similar (63 vs. 64 %) between these two groups. eCG-treated goats exhibited estrus earlier (P <0.05) than the treated goats in contact with the eCG goats. Furthermore, eCG-treated goats had larger litters (1.9±0.2 vs. 1.6±0.1, P <0.05) than the untreated goats in contact with the eCG goats. These results show that fertile estrus can be induced in anestrous female goats by exposing them to female goats induced to estrus with eCG. This female–female interaction triggers the stimulation cycle leading to the sexual arousal of bucks. Keywords eCG . Female effect . Estrus . Ovarian activity . Progesterone Introduction At 26°N, most goat breeds are photosensitive with respect to their reproductive function, with female goats suspending their ovulatory cycles in spring, independent of forage avail- ability (Delgadillo et al. 2012). As a consequence, very few kiddings are likely to occur in the fall, making it difficult for goat producers to provide a consistent supply of goat meat and milk throughout the year. As artificial lighting and the use of hormones are tech- nologies out of reach for extensive goat farmers, farmers wanting to maintain a year-round supply of meat and milk commonly use the “buck effect.” This is an effective and reliable reproductive technique to hasten estrus activity in anestrous goats during the transition period (Véliz et al. 2009; Luna-Orozco et al. 2012). Anestrous mixed-breed goats at 26°N show estrus behavior in response to sexual activity, but only if the bucks were made sexually active by photoperiodic (Rivas-Muñoz et al. 2010) or testosterone R. Rodríguez-Martínez : O. Ángel-García : J. M. Guillén-Muñoz : P. A. Robles-Trillo : M. A. De Santiago-Miramontes : F. G. Véliz (*) Universidad Autónoma Agraria Antonio Narro, Periférico Raúl López Sánchez y Carretera a Santa Fe, C.P. 27054, Torreón, Coahuila, Mexico e-mail: velizderas@yahoo.com C. A. Meza-Herrera Unidad Regional Universitaria de Zonas Áridas, Universidad Autónoma Chapingo, Bermejillo, Durango, Mexico M. Mellado Departamento de Nutrición Animal, Universidad Autónoma Agraria Antonio Narro, C.P. 25315, Saltillo, Coahuila, Mexico Trop Anim Health Prod DOI 10.1007/s11250-012-0305-z