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Serum cholesterol of dairy cattle, particularly when measured on animals of the same approximate age, is a heritable trait. Heritabilities were .50 for first lactation cows and .19 for heifers from 2 to 22 mo of age. Serum cholesterol increases with increasing age. Serum cholesterol was 192.8 mg/100 ml in cows and 121.4 mg/100 ml in heifers. Serum cholesterol was relatively low at the onset of lactation, increased at mid-lactation, and leveled off or decreased in late lactation. Month of calving, year of sampling, and ration did not influence serum cholesterol of first lactation cows. However, variation in both month and year of sampling was significant for heifers.

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