Cow condition drives reproductive performance
As part of her PhD, Agricultural scientist Franzi Weik has been analysing the data set collected from the five large-scale beef operations that participated in Beef + Lamb New Zealand’s beef progeny test between 2014-2019.
Speaking at the recent B+LNZ Genetics field day at Kepler Station (South Island site of the Informing New Zealand Beef across-breed beef progeny test), Franzi says she looked at the phenotypical and genetics influences on body condition and the relationship between body condition score (BCS) and pregnancy.
The cows in the progeny test were weighed and body condition scored three times a year; at mating, weaning and calving. They went through an artificial insemination programme followed by two cycles of natural mating.
She says to optimise conception, the breeding cow needs to be at a BCS of seven at mating. Beyond that there was no benefit in terms of conception rates, but there was a penalty in reproductive performance from having cows at a BCS below seven.
Identifying low condition cows and preferentially feeding them before calving so they can reach a BCS of seven, will help improve reproductive performance at the next mating. This not only increases conception rates, conception happens earlier which helps tighten up the calving pattern.
“The most value will be obtained by reducing the number of low conditioned cows in the herd,” says Franzi. As a rule of thumb, 27kg will shift the BCS by one unit in Angus and Hereford cows.
Franzi says genetics are an additional tool that could be used to help the breeding cow herd maintain condition and get back in calf.
BCS has a heritability of 27 per cent so the right genetics could help lift the BCS of the entire herd by up to one BCS.
“There is potential to identify sires with high genetic merit for BCS but at the moment we don’t have EBVs for BCS to include in our bull selection.”
As part of her research. Franzi looked at the relationship between cow BCS and fat measurements.
While EBVs for fat are valuable from a finishing point of view, they are a blunt instrument when it comes to helping lift BCS in breeding cows.
She says Rib Fat EBVs are an important tool for finishers to help them achieve industry targets of 3-10mm of fat, but they are not good indicators of body energy reserves in cows.
Unfortunately, positive fat EBVs are the only tool farmers currently have in the toolbox, but they should be used primarily to improve the performance of the finishing herd.
The progeny test highlighted big the fluctuations in weight many breeding cows experience over the course of a year.
Franzi says there were big differences between farm and while this could be management and seasonally related, it showed how inter-related liveweight, BCS and reproductive performance are.
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