Mean ovulation rates were 7.1 and 12.1, fertilization rates were 85% and 96%, and recovered embryos considered transferable was 46% and 74% for hot and cool seasons, respectively. A similar study comparing lactating cows with maiden heifers yielded 31% and 63% transferable embryos, respectively, during the summer, with no differences observed during the winter, illustrating the significant effect of lactation on thermoregulation during the summer.