Environmental and Genetic Trends in Production and Their Effects on Sire Evaluation

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Abstract
The objectives of the investigation were to estimate, from DHIA [Dairy Herd Improvement Association] records initiated between Dec. 1956, and Nov. 1962, the magnitudes of the intraherd environmental and genetic trends in the milk and milk fat production of the New York State, Holstein, artificially sired, DHIA population and to determine the effects of these trends on the New York State sire-evaluation procedures. The total intraherd trend was estimated to be 176 [plus or minus] 8 kg of milk and 6. 4 [plus or minus] 0. 3 kg of milk fat per year. Estimates of the intraherd environmental and genetic trends indicated an environmental trend of 128 [plus or minus] 17 kg of milk and 4. 9 [plus or minus] 0. 7 kg of milk fat per year and a genetic trend of 47 [plus or minus] 17 kg of milk and 1. 5 [plus or minus] 0. 6 kg of milk fat per year. Product-moment correlations between standard estimates of sire breeding values and estimates adjusted for the effects of the genetic trend were close to one. However, there were 2 categories of sires where significant differences between the 2 types of proofs were noted: sires that had not recently been used in the population; and sires that had above or below average birth dates and, in addition, had relatively few daughters.