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Journal of Dairy Science Vol. 51 No. 3 428-437
© 1968 by American Dairy Science Association ®
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Genetic and Environmental Parameters of Milk Constituents for Five Breeds. I. Effects of Herd, Year, Season, and Age of the Cow1

M. C. Gacula, Jr.2, S. N. Gaunt and R. A. Damon, Jr.

Departments of Veterinary and Animal Sciences and of Statistics, University of Massachusetts, Amherst

ABSTRACT

The influence of herd, year, season, and age on milk production and composition was investigated on 4,253 lactation records of cows from five major dairy breeds.

A least-squares analysis of the data showed significant effects of herd, year, season, and age on all milk traits studied. The averages of the variance component estimates expressed as per cent of the total variance were: for herd, 15.7 and 11.6% for constituent yields and percentages, respectively; age, 14.6 and 7.3% for yields and percentages; season, 1.9 and 1.4% for yields and percentages; and year, 1.0 and 1.6% for yields and percentages. For younger cows, the least-squares constants for age showed an upward bias of +.10 to +.03% for percentages fat and protein; + .23 to +.04% for per cent SNF; and +.33 to +.05% for per cent TS; whereas, for older cows, the downward age bias was -.04 to -.20% for per cent SNF; -.07 to -.26% for per cent TS; and negligible for percentages fat and protein. A set of multiplicative age factors was derived for each yield trait, and the results suggest two sets of factors, one for milk yield and one for yields of fat, protein, SNF, and TS.

FOOTNOTES

1 A contribution of the Massachusetts Agricultural Experiment Station. This investigation was supported by Hatch 177 and NE-46, The Genetic and Environmental Factors Affecting the Composition of Milk Produced by Dairy Cattle, and from private grants to Dr. S. N. Gaunt, Project Leader. This is part of a thesis submitted by the senior author to the Graduate School of the University of Massachusetts for the Ph.D. degree.

2 Present address: Biometrics Section, Food Research Division, Armour and Company, Oak Brook, Illinois 60521.






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Copyright © 1968 by the American Dairy Science Association ®.