Ovarian function, steroides hormones and fertility in cows stimulated with gonadotropins

To increase profitability in beef and dairy cattle operations, adequate reproductive management strategies that provide high service and conception rates, especially at the beginning of the breeding season for beef cattle, and after the voluntary waiting period for dairy herds, are necessary. To achieve these goals various hormonal protocols have been developed to synchronize the emergence of a new follicular wave, estrus and ovulation, thus allowing fixed time artificial insemination (FTAI). Treatment with eCG has been included in FTAI protocols. Considering that eCG is an indispensable tool for reproductive management, a better understanding of its biological action in the final follicular growth process, ovulation and luteal development is crucial to optimize its use in hormonal protocols. At the same time, alternatives for eCG need to be tested. In this regard, it is important a better understanding of how FSH and LH act in the dominant follicle. Based on that, three studies were performed. The first study evaluated effects of eCG on fertility of 679 crossbred lactating grazing cows synchronized for FTAI. Treatment with eCG tended to increase P/AI at 30 and 60 days and increased P/AI at 30 and 60 days for cows inseminated at ≤ 70 DIM but had no effect in cows receiving AI after 70 DIM. The second study evaluated the effect of eCG or different doses of hCG on the final growth of the dominant follicle in 84 Nelore cows submitted FTAI. No differences were observed for the diameter of the largest follicle on D8 or D10. However, the growth rate of the dominant follicle between D8 and D10 was greater for the groups eCG and hCG 300. In addition, more cows from the Groups hCG 300 and hCG 200 SC presented premature ovulation. Treatment with different hCG doses on D8 of a FTAI protocol failed to produce similar effects compared to eCG. The third study evaluated the effect of eCG, FSH, or hCG on follicular growth rate, ovulatory follicle size, CL volume and circulating E2 and P4 concentrations, as well as the number of large and small luteal cells in cows submitted to a protocol for synchronization of ovulation. Seventeen non-lactating Nelore cows were used. Two Latin squares were done, totaling eight replicates. The gonadotropin treatments, eCG, FSH, or hCG, were effective in increasing the follicular growth rate between D7-10 and consequently the follicular diameter on D10 and ovulatory follicle diameter in comparison to Control. In addition, treatment with different gonadotropins increased the number of large and small luteal cells, however, there was no difference in preovulatory E2 peak concentration, CL volume and circulating P4 concentration post ovulation. (AU)