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Composition of Cows’ Milk. II. Genetic Influences

1968; Elsevier BV; Volume: 51; Issue: 12 Linguagem: Inglês

10.3168/jds.s0022-0302(68)87316-3

1529-9066

N. R. Thompson, Sivakkanan Loganathan,

Animal Diversity and Health Studies

tteritabilities and genetic correlations were estimated from 4,552 records on 3,472 Holstein-Friesian cows by 630 sires.Heritabilities by paternal half-sib correlation of deviations from herdmates were milk yield, .23;fat yield, .09,solids-notfat yield, .22;fat per cent, .45;and solids-not-fat per cent, .47.Heritabilities by regression of daughter on dam with 438 pairs of records were milk yield, .37;fat yield, .22 ; solids-not-fat yield, .27;fat per cent, .55;and solids-not-fat per cent, .25.Genetic correlations among yields were milk fat, .79;milk solids-notfat, .95;fat solids-not-fat, .85.Selection for milk yield should give 94% as much gain in solids-not-fat yield as would direct selection for solids-not-fat yield.Changes in attitudes of consumers may necessitate changes in the composition of market milk.Such changes would include reducing the fat content and increasing the nonfat constituents.Some of these changes can be achieved readily in processing milk.Temporary changes can arise from alterations in nutrition of the cow (7).Changes in milk composition through breeding have been considered, but thoroughly reliable estimates of the genetic and environmental parameters have been lacking (9, 10). Materials and MethodsThe data from Holstein-Friesian cows tested by Dairy Herd Associations in Virginia, 1961 through ]964, included yields and percentages of milk, fat, and solids-not-fat in normal lactations truncated at 305 days or terminated by dry date in <305 days (11).Yields of milk, fat, and solids-not-fat (SNF) were adjusted to mature age by ratios derived from regressions on age within cow from 4,664 records of 3,472 cows with their 630 sires identified.Percentages of fat and SNF were not adjusted.Deviations of 4,552 records from non-half-sib