Evolution of synchronization protocols and use of fixed time artificial insemination in beef cattle in South America

As our understanding of ovarian function in cattle improved, our ability to control it also increased. Although prostaglandin F2α (PGF2α) has been used to synchronize estrus for several years, development of fixed time artificial insemination (FTAI) protocols permitted widespread application of AI for breeding management and genetic improvement in beef herds in South America. Over the last 20 years, a 10 fold increase in AI was largely due to use of FTAI. Main reasons for this growth were the possibility of obtaining acceptable pregnancy rates without estrus detection and induction of cyclicity in lactating cows that were anestrus and heifers that were prepubertal at the beginning of the breeding season. Most FTAI treatments for beef cattle in South America are based on use of progesterone (P4) releasing devices and estradiol to synchronize follicle wave emergence and ovulation, with pregnancies per AI (P/AI) ranging from 40 - 60% ...