Abstract
Based on the considerable differences in ovarian morphology and function, as well as circulating hormones and metabolites between Bos indicus (B. indicus) and Bos taurus (B. taurus), researchers are using this acquired knowledge to optimize protocols for fixed-time artificial insemination (FTAI), and production of in vivo derived embryos by multiple ovulation or by in vitro embryo production (IVP). In B. indicus, at the time of follicle deviation, the dominant follicle is smaller and acquires ovulatory capacity at a smaller diameter than B. taurus. Moreover, despite ovulating smaller follicles and having smaller corpora lutea (CL), circulating concentrations of estradiol (E2) and progesterone (P4) are greater in B. indicus than B. taurus. These physiological differences may be related to greater circulating cholesterol, insulin and IGF1 in B. indicus than in B. taurus. For both genetic groups there is a negative relationship between circulating P4 and ovulatory response to the first GnRH treatment of a fixed-time AI (FTAI) protocol. Moreover, despite lower clearance rates of steroid hormones in B. indicus than B. taurus, the dose of 2 mg estradiol benzoate seems to be the most effective either for Nelore (B. indicus beef), Angus (B. taurus beef), or Holstein (B. taurus dairy) cows at the initiation of an E2/P4-based FTAI protocol to optimize synchronization and pregnancy per AI (P/AI). Several studies have shown that only one recommended dose of PGF2α at a FTAI protocol may be insufficient for adequate luteolysis in B. indicus and B. taurus. When submitted to multiple ovulation and embryo transfer, B. indicus cows and heifers need less FSH than B. taurus to achieve superovulation. Moreover, IVP has been more successful in B. indicus than B. taurus due to greater antral follicle count and anti-mullerian hormone, and better oocyte quality
Highlights
Recent studies have gathered a great deal of knowledge on the reproductive physiology of Bos indicus (B. indicus) heifers and cows, especially by performing direct comparisons with Bos taurus (B. taurus) under similar environmental, nutritional, and management conditions
Accepted: July 11, 2016 function, as well as circulating hormones and metabolites between these two genetic groups. Researchers are using this acquired knowledge to optimize protocols for fixed-time artificial insemination (FTAI), and production of in vivo derived (IVD) embryos by multiple ovulation or by in vitro embryo production (IVP). This manuscript is divided into sections that describe: 1) Differences in reproductive physiology between B. indicus and B. taurus, 2) Practical implications of the physiological differences between B. indicus and B. taurus for FTAI protocols, and 3) Practical implications of the physiological differences between B. indicus and B. taurus for embryo production
Because Nelore (B. indicus) and Holstein (B. taurus) are among the principal beef and dairy cattle breeds used in Brazil, respectively, they are the most representative of the studies discussed in this article
Summary
Recent studies have gathered a great deal of knowledge on the reproductive physiology of Bos indicus (B. indicus) heifers and cows, especially by performing direct comparisons with Bos taurus (B. taurus) under similar environmental, nutritional, and management conditions. We have shown that non-lactating Holstein cows had larger ovulatory follicle diameter (14.2 vs 12.9 mm) and CL volume (5.2 vs 3.9 cm3) than nonlactating Nelore cows (Sartori et al, 2016); Holstein cows had a lower preovulatory peak of circulating estradiol (E2; 12.5 vs 16.2 pg/ml) and circulating progesterone (P4) concentrations (1.9 vs 2.7 ng/ml) on day 7 of the estrous cycle compared with Nelore cows. This inverse relationship between size of ovarian structures and circulating hormone steroids may be related to the reported differences in circulating insulin, IGF1, and cholesterol between breeds. The potential effects of metabolic hormones or other substances on either different clearance rates of steroid hormones or E2 and P4 production by ovarian structures are discussed by Sartori et al (2016)
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