Association of Herd Average Genetic and Environmental Milk Yield with Dairy Herd Improvement Variables

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Abstract
Two hundred fifteen Virginia Holstein herds were used to evaluate the relationship of genetic and environmental herd averages for mature equivalent milk yield with DHIA measures from 1976 to 1980. Herd breeding value was the average of twice the USDA Cow Index for individual cows. Means (.+-.SD) were +243 kg (.+-.107 kg) for genetic value and +685 kg (.+-.757 kg) for environmental value. Herds progressed 31 gk/yr genetically and 122 kg/yr environmentally. Regressions of DHIA variables on genetic and environmental averages were within herd and year. Holding herd and year constant at +250 kg genetic milk, a 600 kg increase in environmental milk resulted in increases of 559 kg herd average milk, 19 kg fat, 13 kg genetic SD, and 0.08 services per conception and decreases of 0.64 d dry, 1.6 d open, 0.48 mo. age at first lactation, and 0.05 mo calving interval. At +700 kg environmental milk, a 150 kg increase in genetic milk was associated with increases of 134 kg milk, 1.9 kg fat, and 0.05 services per conception; and decreases of 0.59 d dry, 4.8 d open, 0.65 mo age at first lactation, and 0.05 mo calving interval. Within herds, environmental improvement tended to be associated with improvement in reproductive measures, and genetic improvement was not detrimental to most measures of herd performance.