34 Reproductive management of beef females in tropical and sub-tropical environments
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AbstractBos indicus and Bos taurus cattle diverged from an evolutionary standpoint more than 110,000 years ago. Since then, Bos indicus cattle have undergone genetic adaptations beyond the commonly discussed increased thermo-tolerance and parasite resistance. Several physiological differences exist between Bos indicus and Bos taurus cattle, and it is important to consider these differences when establishing reproductive management strategies. It has been well described that Bos indicus cattle have a delayed onset of puberty and longer periods of postpartum anestrus, yet through the utilization of estrus synchronization protocols these challenges can be attenuated. However, when Bos indicus females are exposed to these protocols, they are known to have smaller dominant follicles, lower expression of estrus, and decreased pregnancy rates to artificial insemination (AI) when compared to Bos taurus females. These factors can be overcome through the utilization of estradiol and progesterone based synchronization protocols, which improve follicular dynamics and yield acceptable pregnancy rates to assisted reproductive technologies in cattle adapted to tropical or subtropical conditions. However, the use of estrogens for synchronization purposes is not permitted in the United States, and cattle producers need to rely on GnRH-based protocols. Another key difference between subspecies, is that Bos indicus females have greater antral follicle counts than Bos taurus females, which proves beneficial for in vitro embryo production. Therefore, an opportunity exists to explore the greater productivity of donors in embryo production in order to improve genetics in herds that utilize these breeds.
