Effects of the post-partum period on in vivo embryo production in Simmental cows.

The aim of this study was to investigate the effects of post-partum (PP) periods of different lengths on super-stimulatory and super-ovulatory responses, as well as the number and quality of embryos in Simmental cows. Fifty cows were divided into five groups based on their PP days, including 50 - 60 days (n = 5), 61 - 90 days (n = 17), 91 - 120 days (n = 9), 121 - 150 days (n = 9), and 151 - 420 days (n = 10). On a random day of the estrous cycle, all follicles larger than 5.00 mm on the ovaries were aspirated and a progesterone-releasing device was inserted into the vagina of all donors. Approximately 36 hr after follicle aspiration, all cows were administered 500 µg of follicle-stimulating hormone in decreasing doses, twice daily for 6 days. Ovaries were evaluated using trans-rectal ultrasonography during human chorionic gonadotropin treatment and after embryo collection to assess follicles and corpora lutea, respectively. Super-stimulatory and super-ovulatory responses, as well as embryo yield and quality were found to be similar among cows in the PP days groups of 61 - 90, 91 - 120, 121 - 150, and 151 - 420. However, the embryo recovery rate and mean number of transferable and freezable embryos were adversely affected in cows at 50 - 60 days PP. The findings of our study suggested that day 60 PP served as a threshold for in vivo embryo production in Simmental cows.