Effects of Season on Donor and Recipient Cows and Calf Performance from Birth to Weaning in Embryo Transfer Programs in the Tropics

SIMPLE SUMMARY: It is well-known that embryo transfer is a powerful tool which can increase the number of offspring of donor cows, thus improving cattle efficiency. The recipient dams are vital in a successful embryo transfer program, as they will sustain the length of the pregnancy and directly impact the development of the embryo and the productive performance of the animal after birth. Evaluating the effect of season on donors, recipients and delivered offspring from a private farm, we found that the seasonal effect is more apparent in donor and calf performance than in the recipients. It seems to be that the performance of the calves measured by birth and weaning weight favors the embryo-transferred offspring. However, there is a bias towards measuring the performance of calves born by embryo transfer as their condition was favorable compared to calves born by natural mating, as the latter calved at pasture without supervision, whereas the former the recipient dams calved in selected pastures. ABSTRACT: The aim of this study was to assess the seasonal effect of an embryo transfer program in the tropics on the donor response, recipient reproductive performance and calf growth from birth to weaning. This study included five-year records from 145 donors, 1149 embryo transfers (ET) and 609 in calves. The effect of the season (dry or wet) was evaluated at the time of embryo flushing, embryo transfer and birth of the calves. There was a seasonal effect on the yield and quality of the embryos. The number of nonfertilized and transferable good quality embryos increased in the wet season. For the recipients, the probability of pregnancy after an ET decreased by 6% for each year of the dam’s age. However, no seasonal effect was found when comparing ET calves with their control group (natural mating—NM), nevertheless, weaning weight was associated with birth body weight, treatment, sex of the calf, season at birth, year of treatment, and dam’s age. Calves born by NM had lower average daily gain (ADG), and male calves registered higher gains than females. Likewise, calves born during the rainy season had lower ADG compared with calves born during the dry season. In conclusion, this study shows that seasonal effect is more apparent in donor and calf performance than in the recipients.