GENETIC, ENVIRONMENTAL, AND PRICING INFLUENCES ON MILK AND MILK COMPONENT PRODUCTION
- Author
- Mbah, David Akuro
- Physical Description
- 88 pages
- Additional Creators
- Pennsylvania State University
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- Summary
- First lactation modified contemporary deviation data of 8150 daughters of 1087 sires calving from August, 1972, to October, 1977 (1974 for Guernsey and Brown Swiss) in 205 herds of Pennsylvania Dairy Herd Improvement were used. Estimates of genetic parameters for milk and milk constituents, common environmental correlation among paternal half-sisters in the same herd, and genetic changes through selection indexes including protein pricing were made. Genetic parameter studies included 112, 158, 1523, 273, and 85 Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss records, respectively. Corresponding to these records were 31, 42, 216, 62, and 22 sires. Common environmental correlation studies included 332, 346, 1848, 703, and 184 Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss records by 36, 67, 301, 112, and 47 sires, respectively.
Mean performance was high. Holsteins were highest in yields but lowest in percentages. The reverse was true of the Jerseys.
All breeds, except the Holstein, produced some genetic parameter estimates outside theoretical limits. The following results are from Holstein data. Heritability from paternal half-sib correlations was .27, .26, .09, .75, and .32 for milk, fat, and protein yields, fat, and protein percentages, respectively. Genetic correlations were .44 -1.00, -.56, -.86, .87, .49, .11, -.16, -.71, and .96 between milk yield and yields of fat and protein, between milk yield and percentages of fat and protein, between fat and protein yields, between fat yield and percentages of fat and protein, between protein yield and percentages of fat and protein, and between fat and protein percentages, respectively. In the same order, phenotypic correlations were .80, .89, -.30, -.27, .82, .31, .01, -.10, .16, and .46.
The heritability of the carrier (milk yield minus protein yield minus fat yield) was .28 while genetic correlations between it and protein and fat percentages were -.88 and -.59, respectively. Phenotypic correlations were correspondingly -.30 and -.33. These genetic and phenotypic parameters are stronger than in whole milk.
Common environmental correlations estimated as the difference between two intraclass correlations among paternal half-sisters in the same and different herds were .05, .10, .16, -.06, and .13 for milk, fat, and protein yields, fat, and protein percentages, respectively. This suggests stronger common environmental effect on protein traits than other traits.
Selection emphasis on index traits, genetic change per trait, and total genotypic change are determined by the economic importance of index traits. With variable postulated economic values, most indexes indicated gain in the carrier but loss in percentages. Gain in percentages was associated with loss in the carrier. When protein was not part of the selection program, but was part of the payment scheme, net economic returns from selection gain were at least 92% of those from a full selection program, depending on the distribution of selection emphasis in the full model program. - Other Subject(s)
- Dissertation Note
- Ph.D. The Pennsylvania State University 1980.
- Note
- Source: Dissertation Abstracts International, Volume: 41-03, Section: B, page: 8160.
- Part Of
- Dissertation Abstracts International
41-03B
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