Reproductive tract scoring by trans-rectal palpation using a 5-point scale was
performed by a single operator on all heifers either 1 or 2 days before the onset of their
first breeding season (Andersen et al., 1991). Scores 4 and 5 were combined in the
analyses, after assuming that both categories were pubertal at the time of scoring
(Stevenson et al., 2008), and were used as the reference category in Cox proportional
hazards and logistic regression models. It was further assumed that heifers with RTS 3
were peripubertal and that those with RTS 1 or 2 were prepubertal, which were also
combined in the analyses (Stevenson et al., 2008). Body condition score (BCS) was
determined at the same time by the same operator using a 9-point scale (Marston, 2005).
For the purpose of regression models and survival analysis, BCS was categorized into 2
approximately equal sized categories: BCS ≤ 6 and BCS 7, because relatively few
heifers were recorded to have BCS < 6 and BCS > 7. Farm management and staff were
blinded to RTS data throughout the study.