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Journal of Dairy Science Vol. 50 No. 12 1897-1904
© 1967 by American Dairy Science Association ®
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Environmental Influences on Monthly Variation in Milk Constituents

P. W. Spike and A. E. Freeman

Department of Animal Science, Iowa State University, Ames

ABSTRACT

Least-squares techniques were used to estimate the effects of age of cow, stage of lactation, month of year, and the two-factor interactions of age with stage and month with stage, on milk and its constituents. The analyses were done within breeds, and herd effects were absorbed. There were 303,193 monthly observations from 26,414 cows of six breeds. All cows were enrolled in Dairy Herd Improvement Associations in their respective states. The traits considered were the test day production of milk, milk fat, solids-not-fat (SNF), total solids (TS), and the percentage composition of the three constituents. SNF percentage was determined by the Golding plastic bead procedure.

The reduction due to fitting the set of constants for each main effect and each of the interactions was large and gave a highly significant (P < .001) F-ratio for all traits. The interaction of month and stage accounted for a very small proportion of the total variance. Although this effect is real, it is of small magnitude. The interaction of age with stage indicated that incomplete lactations of cows of different ages require different factors for extrapolating to complete lactations, for all constituents.

FOOTNOTES

1 Journal Paper no. J-5671 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project no. 1053. This research was part of the North Central Eegional Project NC-2.






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Copyright © 1967 by the American Dairy Science Association ®.