Heavy calvers not so good…
PUSHING heifers to high weights of 625kg at first calving may be worse than calving them at 540kg, as lighter animals appear to look after themselves better during their first lactation.
Researcher Alistair Carson said while these heavier heifers produced 6-9% more milk protein and fat in their first lactation, this only partially offset the increase in rearing costs.
Speaking at the BSAS conference in Scarborough, he said that 113 heifers from 11 farms were reared at the Agricultural Research Institute of Northern Ireland, Hillsborough, Co Down. Heifers were returned to their owners a week before calving to show their performance under a typical range of NI systems.
"Smaller, lighter heifers mobilised less body fat and lost less condition. By the end of the first lactation there was no difference in body weight between light and heavy heifers at calving, although the light ones were skeletally smaller," he said.
"There may be additional benefits of not mobilising body reserves; in the study we observed a shorter interval to first oestrus in the light heifers."
This research goes against advice currently given to producers about Holstein type heifers needing to be heavier at first calving, he said.
The NI research indicates that body weight is less important to first lactation performance and that it proves less economic to rear heifers to reach heavier weights. But the final economics will depend on second and further lactation performance, he added.
The institute will continue to aim for heifers to reach 570kg at calving for its dairy herd, added Dr Carson. "We havent been encouraged to increase that to 620kg from our studies to date."