Short communication: seasonal effects on development of bovine embryos produced by in vitro fertilization in a hot environment.

The objective of this study was to determine if season affected the production of in vitro-derived bovine embryos from oocytes of cattle in a subtropical environment. Ovaries (approximately 75% beef cattle, including many with Bos indicus breeding) were collected from an abattoir. Oocytes were obtained and subjected to in vitro maturation and fertilization. Embryos were then cultured in CR1aa medium. Cleavage rate averaged 72.2+/-9.7% and was not different between months of collection. In addition, no differences were observed in the percent of oocytes or embryos that became blastocysts on d 8 or 9 after insemination. Least-squares means averaged across months for percent oocytes and cleaved embryos to blastocyst on d 8 were 22.8+/-7.5% and 31.2+/-9.4%, respectively. When d 8 blastocysts were classified according to stage of development (nonexpanded, expanded, and hatched), an effect of month was observed that reflected month-to-month variation and not a consistent change associated with season. Taken together, results failed to indicate an effect of season on in vitro production of embryos in a subtropical environment.