Variations in Yield of milk under the Penkeeping System in Brazil

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Abstract
Milk production records over a period of 8 years on a large dairy farm in Brazil where the cows are with their calves on pasture during the day, separated from them during the night, and milked only in the morning yielded the following conclusions. Year-to-year differences were significant. Only part of those could be ascribed to a linear upward trend of about 1.4% per year and the statistical significance of that trend was uncertain. Yields were highest toward the middle and end of the rainy season and lowest late in the dry season, but those seasonal differences were small. Production was maximum around 40 to 50 days after calving. Thereafter it declined in nearly a straight line and at a percentage rate closely similar to that of dairy cows in temperate regions. The sex ratio showed a slight but significant excess of [male] [male]. Heritability of individual differences in milk yield seemed moderately high.

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