Abstract:
In this study, 272 beef heifers were
studied from just before their first breeding season (October
15, 2003), through their second breeding season,
and until just after they had weaned their first calves
in March, 2005. This study was performed concurrently
with another study testing the economic effects of an
estrous synchronization protocol using PG. Reproductive
tract scoring (RTS) by rectal palpation was performed
on the group of heifers 1 d before the onset of
their first breeding season. The effect of RTS on several
fertility and production outcomes was tested, and the
association of RTS with the outcomes was compared
with that of other input variables such as BW, age,
BCS, and Kleiber ratio using multiple or univariable
linear, logistic, or Cox regression. Area under the curve for receiver operating characteristic analysis was used
to compare the ability of different input variables to
predict pregnancy outcome. After adjustment for BW
and age, RTS was positively associated with pregnancy
rate to the 50-d AI season (P < 0.01), calf weaning
weight (r = 0.22, P < 0.01), and pregnancy rate to the
subsequent breeding season (P < 0.01), and negatively
associated with days to calving (r = 0.28, P < 0.01).
Reproductive tract scoring was a better predictor of
fertility than was Kleiber ratio and similar in its prediction
of calf weaning weight. It was concluded from
this study that RTS is a predictor of heifer fertility,
compares well with other traits used as a predictor of
production outcomes, and is likely to be a good predictor
of lifetime production of the cow.
