The objective of this research was to partition phenotypic variation in calf gain from birth to weaning, and milk production measured, by the weighsuckle-weigh method, and udder score of cows into genetic and nongenetic components. Data were from the Line 1 Hereford population maintained by USDA-ARS at Miles City, MT, and included observations of preweaning gain (n = 6,835) from 2,172 dams, mil...