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Genetics of production, type and herd life in dairy cattle
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Dissertation
Genetics of production, type and herd life in dairy cattle
1994
Overview
The main objective of this work was to undertake analyses which would lead to an improvement in the accuracy of production and type breeding value predictions for Holstein-Friesian dairy cattle and to investigate the relationship between production and type traits and herd life. Production records were obtained from the National Milk Records files and linear type records from the Holstein Friesian Society. An animal model estimation of heterosis and recombination loss between North American Holstein and European cattle for first lactation milk, fat and protein yield showed that the omission of these effects in breeding value prediction would bias the results. Including both these effects in the breeding value estimation increased the predicated sire proof for fat plus protein yield of a typical F1 Holstein X Friessian sire by 3kg. An analysis of approximately 275 000 first lactation records and the 2nd to 5th lactation records of survivors found the regression coefficients of yield in lactations 1 to 5 on heterosis and recombination loss to be fairly consistent over lactations. After fitting first lactation yield in the model and compared to a pure Friesian, there is an increased chance of survival to third lactation of 3.6% for a pure Holstein, 3.8% for an F1 and an F2, and 2.4% for a Friesian backcross. In the investigation of herd life, defined as the completion of a specified number of lactations, in relation to linear type traits and production, results were not completely consistent either over lactations or over different subsets of the population. In general, there was a significant positive association between survival and angularity, fore udder attachment and udder depth and a negative association with chest width, rump width and teat length. Regressions on yield were positive, while those on fat and protein content were usually negative.
Publisher
ProQuest Dissertations & Theses
Subject
