Male effect and breeding season shortening under contrasting climatic conditions upon reproduction of nulliparous Anglo-Nubians / Efeito do macho e redução das estações de monta em diferentes condições climática a reprodução de nulíparas Anglo-Nubiana

ABSTRACT

This study was aimed to evaluate breeding seasons of different durations under contrasting climatic conditions upon reproductive performance of nulli­parous does submitted to male effect. A total of 240 Anglo-Nubian females at 8 to 12 months of age were used and were kept away from all three bucks at a distance of 300 m for 60 days, which avoided any physical, visual, olfactory or hearing contact between genders. Estrus were visually detected and pregnancy rates were determined by ultrasonography 60 days after the last mating. Breeding season duration and climatic condition did not influence estrus incidence, where 70% does had estrus detected at the dry season, 80% of does cycled at the rainy season within breeding seasons of 25 days. Moreover, 80% of does cycled at the dry season and 95% at the rainy season during breeding seasons of 35 days and 45 days. After breeding seasons of 25 days, pregnancy rate was lower at the dry season (55.0%) compared to the rainy season (80.0%). Mean birth weight of resulting offspring was lower during the rainy season (2.94 kg ± 0.26) than during the dry season (3.03 kg ± 0.16). The results show that estrus onset is affected by breeding season durations and climatic conditions tested, although dry season lowered pregnancy rates. In conclusion, 25-day breeding seasons are recommended to improve standardization of offspring lots, to reduce costs with food supplementation and estrus detection, while preserving pregnancy and kidding rates.