Genetic analysis of milking temperament and its relationships with milk production traits in South African holstein cattle.
Siwele, Thuli Tintswalo
Siwele, Thuli Tintswalo
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Abstract
Milking temperament (MT) is an important functional trait in dairy cattle, as it influences herd profitability, human and animal welfare. There is, however, limited knowledge such as genetic parameter estimates on MT in South African Holstein cattle, which makes it difficult to improve the trait genetically. The aim of this study was to estimate genetic parameters for MT and its relationships with milk production traits (milk yield, fat and protein) in South African Holstein cattle. Data consisted of MT scores on 2 844 cows from 16 herds participating in the National Milk Recording and Improvement Scheme, recorded from September 2020 to November 2021. Corresponding test-day records of milk yield and composition, and pedigree information, were obtained from the Integrated Registration and Genetic Information System of South Africa. Analysis of variance was performed using the General Linear Models procedure of the SAS software, to determine non-genetic factors affecting MT and milk production traits. Repeatability of MT scores was estimated using the variance components procedure of the SAS software. Genetic parameter estimates were obtained by linear animal models, using the ASReml software. Herd test-day, age of cow at calving (P <0.0001) and lactation stage (P <0.05) had significant effects on MT. The repeatability estimate for MT scores was moderate (0.47), while the estimate of heritability was low (0.05±0.04). Heritability estimates for milk production traits were low to moderate, ranging from 0.11±0.05 for milk yield to 0.24±0.06 for protein %. Milking temperament had a moderate and favorable genetic correlation (0.60±0.35) with milk yield. In contrast, low and unfavorable correlations were observed for MT with fat % (-0.12±0.24) and protein % (-0.30±0.32). Phenotypic correlations were also positive for MT with milk yield (0.25±0.02) and negative with fat (-0.06±0.03) and protein % (-0.04±0.02). There was no discernible genetic trend for MT, for animals born from 2009
to 2019, and a marginal overall decline was observed over the period. These results indicate reasonable consistence in the assessment of MT in the current study, and suggest that there is scope to improve MT through selection, using multi-trait models including milk yield.
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Submitted in partial fulfilment of the requirements of the degree, Master of Agricultural Science, in the Department of Animal Sciences, Faculty of Science
Date
2023-11
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Tshwane University of Technology
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Keywords
dairy cows, milking behaviour, genetic improvement, milk composition