Short-term exposure of high body weight heifers to testosterone-treated steers increases pregnancy rate during a late autumn-early winter natural service

Ungerfeld, R

Exposure to bulls seem to stimulate cyclic activity in postparitum beef cows, hasten puberty and increase pregnancy rate in heifers. The aim of this experiment was to determine if short-term exposure of pubertal beef heifers to testosterone-treated steers prior to late autumn-early winter bull breeding would increase pregnancy rates. An . Pregnancy was determined on Days 60 and 75. On Day 60, no differences were observed between groups in the frequency of pregnant heifers (18.2 vs 7.7% pregnant). On Day 75, more heifers in the biostimulation group that had an initial body weight ≥310 kg were pregnant (61.1 vs 32.4%, for stimulated and non-stimulated heifers respectively, P = 0.016), whereas there were no significant differences in heifers with lower initial body weight (17.9 vs 30.3% pregnant, for stimulated and non-stimulated heifers respectively). In conclusion, pregnancy rate was increased in high body weight heifers during late autumn-early winter natural service following pre-breeding exposure of the heifers to testosterone-treated steers.(AU)

1. male effect
2. socio-sexual signals
3. biostimulation
4. puberty