Circulating progesterone at insemination and accessory spermatozoa are associated with fertilization and embryo quality five or six days post insemination in dairy cattle

This study aimed to evaluate animal and ovarian parameters that affected fertilization and embryo development up to the morula stage. The data were combined from four studies in which cows were inseminated between 46 and 60 days in milk, following a synchronization protocol, and flushed for embryo collection five or six days later. Parity and body condition score on the day of insemination were recorded. Cyclicity, ovarian structures, and circulating hormone concentrations before and on the day of insemination were also assessed. The recovered structures were graded on a 5-point scale (excellent-good quality, fair quality, poor quality, degenerated, and not fertilized). For recovered embryos, the total number of blastomeres, the number of nonviable blastomeres, and the number of accessory spermatozoa were assessed by epifluorescence microscopy. The risk factors for fertilization and embryo quality were identified using cumulative link mixed models. A total of 418 structures from 389 lactating Holstein cows (34% primiparous and 66% multiparous) were recovered. Thirty-five percent of the recovered structures were excellent-good quality embryos, 21% were fair quality embryos, 11% were poor quality embryos, 16% were degenerated embryos, and 17% were unfertilized oocytes. Structures from primiparous cows, from those with greater progesterone concentration at insemination, and from cows with seven or less accessory spermatozoa were less likely to be fertilized or of better quality than structures from multiparous cows, from those with lower progesterone concentration in plasma, and from those with more than seven accessory spermatozoa, respectively. Embryos with more blastomeres or without nonviable blastomeres were more likely to be of better quality than embryos with fewer blastomeres or with nonviable blastomeres. The results of this analysis highlight the importance of low circulating concentrations of progesterone near artificial insemination and potential positive association with number of accessory spermatozoa reaching the embryo and improvement of embryo development up to the morula stage.