Bias against ‘early maturers’ did not have a negative effect on calving interval EBVs
Take Home Message: Estimated breeding values for calving interval are not influenced by management decisions on when to re-breed.
Any bias against early maturing British Limousin heifers from management decisions on when to re-breed did not adversely affect the calving interval estimated breeding values (EBVs).
That’s what a team of scientists at the Scottish Agricultural College found during a study to investigate if calving interval (CI) EBVs produced by the British Limousin genetic evaluation were affected by management decisions.
“We also wanted to assess if reducing the season slice, in other words reducing the chance of directly comparing early and late calvers, for the CI contemporary group improved the CI model,” SAC’s Kirsty Moore told delegates at this year’s British Society of Animal Science annual conference.
Female fertility is an important component of a beef production system and in the British Limousin genetic evaluation there are several female fertility traits recorded. Two of these traits are calving interval (CI) and age at first calf (AFC).
In British beef breeds there are estimated to be moderate negative genetic correlations between CI and AFC; early maturing animals (low AFC) had longer CI because of genetic factors.
“But it has also been suggested that management factors could be increasing the CI EBV of early maturing animals,” said Miss Moore, explaining the rationale behind the team’s work.
“Does, for example, the CI EBV account for heifer’s that calve early for the first calf, but then are not given the opportunity to re-mate when they first return to oestrus, and therefore, may have a longer raw CI record? We wanted to find out.”
For the study, CI was defined as the number of days between a heifers first and second recorded calf. EBVs were produced using software based on Best Linear Unbiased Prediction.
The model consisted of the contemporary group (CG), birth month of the first calf and the Limousin breed proportion as fixed effects, the linear and quadratic effect of the raw AFC and the heifer fitted as a random effect. The CI CG was defined by the herd, year and season of the first calf’s birth, with season being a six month time period.
“And analysis revealed that within individual herds and contemporary groups, there may be bias against early calvers. But with limited information recorded it is difficult to identify these CG and account for differences in mating appropriately,” said Miss Moore.
“With the small CG sizes despite a broad CG definition, this study highlighted the small amount of information available for maternal traits. As more information is recorded, reducing the length of the season slice may improve the CI EBVs but in this study, reducing the season length did not appear to improve the CI EBVs,” she added.
summary (pdf) presentation ([pdf)
To view proceedings of all summaries presented at the Annual Conference 2009 http://www.bsas.org.uk/Publications/Annual_Conference_Proceedings/ To view all Powerpoint presentations http://www.bsas.org.uk/Members_Area/ For further information contact: BSAS on 0131 445 4508 or bsas@sac.ac.uk
