Although not the case for the 2003 cohort, all heifers in the study with RTS 1 and
2 combined (compared to RTS 4 and 5 combined) were more likely to fail to become
pregnant during their first AI season, after adjusting for 24-day anoestrus, pre-breeding
BW and age (Table 3). Even when excluding those heifers in anoestrus during the entire
50-day AI season, heifers with RTS 1 and 2 combined were more likely to fail to become
pregnant than those with RTS 4 and 5 combined (OR = 1.9, P = 0.043). The random
effect of AI bull in the logistic regression model of pregnancy failure during the first AI