HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Butcher, K. R. Articles by Legates, J. E. Search for Related Content PubMed PubMed Citation Articles by Butcher, K. R. Articles by Legates, J. E.

Estimates of Genetic Parameters for Milk Constituents and Yields¹

Department of Animal Science, North Carolina State University at Raleigh

ABSTRACT

Genetic parameters were estimated and selection alternatives for milk yield and its major constituents examined, using 3,841 lactation records from Holstein cows in the North Carolina Institutional Breeding Association. Heritability estimates from the daughter-dam regressions were 0.28, 0.17, 0.24, 0.21, and 0.21 for milk, fat, PLM, (protein-lactose-mineral), TS (total solids), and protein yields, respectively, and 0.62, 0.53, 0.60, and 0.47 for fat, PLM, TS, and protein percentages, respectively. Within herd-year-season phenotypic correlations between milk yield and the percentages all were negative, whereas correlations among constituents were strongly positive. Genetic correlations were -0.61 between milk and fat per cent, -0.43 between milk and PLM per cent, -0.45 between milk and protein per cent, 0.69 between fat and PLM percentages, 0.74 between fat and protein percentages, and 0.82 between PLM and protein percentages. Direct selection for PLM yield would give an expected correlated genetic change in milk yield close to that expected from direct selection for milk yield. Selection for fat or protein yield would be expected to result in a substantial reduction in milk yield compared with direct selection for milk yield. Selection for milk or PLM yield would result in moderate to large expected decreases in the percentages. Efforts to increase, prevent declines in, or change the proportions of the constituents appear to be costly in terms of selection pressure which can be applied to the yield traits.

¹ Contribution from the North Carolina Agricultural Experiment Station, Raleigh, North Carolina. Published with the approval of the Director of Research as Paper no. 2253 of the Journal Series.