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Composition of Cows' Milk. I. Environmental and Managerial Influences ¹

Department of Dairy Science Virginia Polytechnic Institute, Blacksburg

ABSTRACT

Means and standard deviations for 4,664 age-adjusted 305-day lactational records on 3,472 Holstein-Friesian cows were milk 6,820 ±1,384 kg; fat, 3.67 ± .41% and 245 ± 50 kg; solids-not-fat, 8.51 ± .37% and 560 ± 112 kg. Age at calving accounted for 10.0–14.3% of the total variance in milk, fat, and solids-not-fat yields, and days milked for 14.0–18.0%. Month of calving accounted for 0.5–5.8%, days carried calf for 0.1–1.2%, and body weight for zero to 0.8% of the total variance in yields. Age at calving and days carried calf affected solids-non-fat per cent significantly and accounted for 12.4 and 0.4%, respectively, of the total variance. Fat per cent was not affected significantly by any of the factors.

Lactational records of milk, fat, and solids-not-fat yields before comparing with one another or for use in genetic analyses should be adjusted for age at calving, number of days milked, and month or season of calving.

¹ Research supported in part by grants from the Dairy Foundation of Virginia, Inc.

² Present address: Department of Biology, Shepherd College, Shepherdstown, West Virginia.