In the multivariate analysis, the interaction between treatment of cows with GnRH on
Day 5 and Day 15 on pregnancy rate tended to be significant (P < 0.10). Administration of
GnRH on Day 15 tended to decrease pregnancy rate on Day 27 only in cows previously
treated with GnRH on Day 5. In addition, there was an effect (P < 0.01) of season on
pregnancy rate. Therefore, the final model to evaluate pregnancy rates on Days 27 and 55
and pregnancy loss between Day 27 and Day 55 included group and season.