Evolution of knowledge on ovarian physiology and its contribution to the widespread application of reproductive biotechnologies in South American cattle.

Reuben J Mapletoft,Roberto Sartori,Pietro S Baruselli,Alejo Menchaca,Gabriel A Bó

doi:10.21451/1984-3143-ar2018-0007

Abstract

As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. Luteal function in cattle has been studied in detail, and prostaglandin F2α has been used for several years for the elective induction of luteal regression. More recently, follicle wave dynamics has been studied and protocols designed to induce follicular wave emergence and ovulation have reduced, and even eliminated, the need for estrus detection. The addition of progestin-releasing devices, estradiol, GnRH and equine chorionic gonadotropin (eCG) have provided opportunities for fixed-time AI (FTAI) and possibilities for increased pregnancy rates. In embryo transfer programs, these same treatments have eliminated the need for estrus detection, permitting fixed-time embryo transfer and the initiation of superstimulatory treatments without regard to day of the estrous cycle. Collectively, new treatment protocols have facilitated the application of assisted reproductive technologies, and this is especially true in South America. Over the last 20 years, the use of AI in South America has increased, due largely to the use of FTAI. There has been more than a 10-fold increase in the use of FTAI in Brazil with more than 11 million treatments in 2016, representing 85% of all AI. Similar trends are occurring in Argentina and Uruguay. Production of in vivo-derived (IVD) embryos has remained relatively stable over the years, but in vitro embryo production (IVP) has increased dramatically over the past 10 to 15 years, especially in Brazil where more than 300,000 IVP embryos were produced in 2010. World-wide, more than 666,000 bovine IVP embryos were produced in 2016, of which more than 57% were produced in South America. The use of assisted reproductive technologies has facilitated the dissemination of improved genetics and increased reproductive performance; other South American countries are now following suit.

Highlights

Increasing knowledge of ovarian physiology in cattle over the past 50 years has provided approaches for the manipulation of ovarian function
Pregnancy rates following fixed-time AI (FTAI) have been shown to be improved in suckled beef cows and heifers, especially B. indicus crosses, when 300 to 400 IU of equine chorionic gonadotropin (eCG) is administered at the time of progestin removal (Baruselli et al, 2004; Bó et al, 2012; 2016)
To minimize animal handling and the suppressive effect of progesterone on follicle growth, Prostaglandin F2α (PGF) is often administered at the beginning of the protocol, and estradiol cypionate (ECP) is administered at the time of progestin device removal with FTAI 48 hours later

Summary

Introduction

Increasing knowledge of ovarian physiology in cattle over the past 50 years has provided approaches for the manipulation of ovarian function. Transvaginal ultrasound-guided ablation of antral follicles results in emergence of a new follicular wave in approximately 1.5 days by removing the suppressive effects of follicle products (e.g., estradiol and inhibin) on FSH release (Bergfelt et al, 1994; Fig. 2). In early estrus synchronization protocols, 2.5 mg EB is administered at the time of insertion of a progestin device which is removed 7 days later, at the time of administration of PGF (Mapletoft et al, 2003).

Results

Conclusion