A study was conducted to estimate the phenotypic, environmental and genetic changes occurring in populations of Angus (A) and Hereford (H ) cattle in Virginia as a result of 20 to 30 years of performance testing. Over a period of five cattle generations 205-d weaning weights (WW) increased about 30 kg in each breed. The evidence indicated that more emphasis was placed on sire than on dam selection. Estimates of both sire and dam trends were positive for most of the 13 A and 11 H herds studied, with most change occurring in the later years. The maximum likelihood method of estimation appears to be the more desirable method for these data.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume IX. Breeding programs for dairy and beef cattle, water buffalo, sheep, and goats., , 424–429, 1986
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