Genotype by Environment Interactions for Milk and Fat Production Across Regions of the United States

(Co)variance components for regional production of milk, fat, and fat percentage were estimated via multiple-trait REML using DHIA data from California, New York, and Wisconsin. Data consisted of registered and grade first lactation yields of Holstein cattle from 1970 through 1984. Records were limited to daughters from sires common to the pairs of states analyzed. Averaged numbers of records from California, New York, and Wisconsin were 419,185, 460,296, and 449,866. Genetic correlations between New York and Wisconsin for milk, fat, and fat percentage (.99, .98, and .99) were larger than those between California and New York (.95, .95, and .98) and those between California and Wisconsin (.94, .93, and .98). Heritabilities in New York for milk, fat, and fat percentage (approximately .27, .26. and .48) were larger than those of Wisconsin (approximately .23, .22, and .43) and California (approximately .22, .21, and .34). Grade records were also investigated; numbers of records in California were reduced by about 25%. whereas records in both New York and Wisconsin were reduced by about 66%. Genetic correlations were virtually unchanged, but heritabilities for milk and fat in the three states were similar (approximately .17) and significantly smaller than those from combined registered and grade daughters. In concluReceived March 7.1989. Accepted May 29,1989. ‘Present address: Depanamento de GenCtica, Institute Nacional de Investigaciones Agarias, Carretera de La CONUa, km 7.28040 Madrid, Spain. hesent address: Department of Animal Science, University of Nebraska, Lincoln 68583. sion, there appeared to be no sire by region interaction. (