Genetic selection for litter size in cattle (#28)
Efficiency of production in beef cattle is limited by their relatively
low reproduction rate. In this paper, we present the results of a fourteen year
breeding program aimed at increasing prolificacy in a mixed beef x dairy herd, grazing
at Armidale in the New England region of NSW. The herd was established by
purchasing cows with a repeated history of twinning and bulls from dams with
unusually high prolificacy. For the 51foundation cows with at least one
subsequent calving record, the average prolificacy was 1.11 +/- 0.05 (123 total
records. For all cows born in the herd, the mean ovulation rate was 1.12 and
the mean prolificacy was 1.03. The twinning rate was lower than expected based
on reports from other experimental herds
aimed at increasing prolificacy that have been established in the USA, New
Zealand and France. The observed genetic trends for ovulation rate and
prolificacy were essentially zero but were moderately positive for fertility,
cow rearing ability and reproduction rate. The desired outcome of generating a
positive genetic trend in reproduction rate was achieved, albeit to a limited
degree, but not as a result of genetic response in ovulation rate or prolificacy,
the traits under direct selection pressure.