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Progeny testing in beef cattle can be used to provide phenotypes for estimating carcase trait breeding values. However, progeny are commonly selectively slaughtered over time based on live-animal indicators of market requirements for carcase traits, particularly if feedlot finished. This harvesting results in carcase trait records for non-random groups of animals because harvesting on liveweight (LWT) causes the progeny of genetically faster growing sires to be in earlier harvest groups. This can lead to confounding of genetic and harvest group effects in genetic evaluation models. Additionally, harvesting can lead to the effect of age not being partitioned. Therefore, the aim of this thesis was to find appropriate statistical methodology that can be applied to harvested data to give unbiased and accurate estimated breeding values (EBVs) for carcase traits. ... The study gives evidence that appropriate trait adjustments for age along with certain models are able to estimate accurate and unbiased sire EBVs for harvested data. This holds for data affected by specific harvest day effects, including for age-influenced carcase traits varying in level of genetic correlation with the harvesting criteria. |
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