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Journal of Dairy Science Vol. 50 No. 2 177-184
© 1967 by American Dairy Science Association ®
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Environmental Influences on Milk Constituents1

F. D. Sargent, K. R. Butcher and J. E. Legates

Department of Animal Science North Carolina State University at Raleigh

ABSTRACT

The influence of some major environmental factors on milk composition was investigated in 2,936 complete lactations, from nine Holstein herds in the North Carolina Institutional Breeding Association. Ratio extension factors for incomplete lactations were developed for milk yield and percentages of fat, protein, and PLM (protein-lactose-mineral). Age at freshening accounted for 21.7, 14.3, 5.3, and 1.9% of the variance in milk yield and PLM, protein, and fat per cent, respectively, on a within-herd-year-season-sire basis. Days open prior to conception accounted for 6.8 and 0.4% of the variance in milk yield and PLM per cent, but no significant influence on fat or protein per cent was evident. Differences between month of freshening were significant for milk yield and PLM and protein per cent, but not significant for fat per cent. The two six-month seasons, November to April and May to October, account for most of the seasonal variation in milk yield and milk composition. Cows freshening in November through April had the highest average milk yield; whereas, cows freshening from May through October had the highest average percentage values for the milk constituents.

FOOTNOTES

1 Contribution from the North Carolina Agricultural Experiment Station, Raleigh. Published with the approval of the Director of Research as Paper no. 2252 of the Journal Series.






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Copyright © 1967 by the American Dairy Science Association ®.