Genetics
of a reproduction-based
selection program.
Researchers looked at the age,
weight and growth rate of
heifers successfully conceiving
to AI or natural service using
14 years of data collected
throughout development.
Weights were collected at late
October weaning, February
mid-winter development, April
pre-estrus synchronization,
158 | JUNE/JULY 2018
late May AI, mid-July
pregnancy check and mid-
September pregnancy check. selection for early puberty
has benefits at weaning with
older, likely heavier calves.
Heifers cycling prior to estrus
synchronization were older
and heavier at all pre-breeding
weigh-ups, and were the
only ones bred AI. Previous
work suggests heifers are
more likely to calve early in
the calving season if cycling
prior to breeding season, so If you just want pregnant heifers
after AI or natural service,
rather than opens, results
are similar: pregnant heifers
had been older and heavier
at weaning and remained
heavier through the September
pregnancy diagnosis. Weight
gain from weaning to the April