Genetic change in milk, fat, days open, and body weight after calving based on three methods of sire selection

Three Holstein lines, were compared, based on different methods of sire sel ection, for genetic change in 3.7% FCM, fat yield, days open, and predicted body weight after calving. The three lines were 1) evaluated sires selecte d only for 3.7% FCM (milk line), 2) evaluated sires selected on an index th at included 3.7% FCM and type traits tinder line), and 3) young bulls selec ted on pedigree for 3.7% FCM (young line). Cows from these lines were born in 1971 through 1993 in five experimental herds owned by the State Farm Div ision of North Carolina Department of Agriculture. Breeding values of cows in each line computed with a repeatability model were averaged by and regre ssed on birth year to estimate genetic change. Genetic gains in 3.7% FCM we re 81 kg/yr for the milk line, 61 kg/yr for the line selected on index, and 68 kg/yr for the young sire line, Estimates of genetic gain in fat yield w ere 2.99, 2.16, and 2.54 kg/yr in the three lines, respectively. Genetic ga ins in 3.7% FCM and fat yield in the milk line were significantly different from the index and young sire lines, but the index and young sire lines we re not significantly different. Estimates of genetic change in days open we re 0.71, 0.57, and 0.63 d/yr in the milk, index, and young sire lines, resp ectively. These estimates were not significantly different. Average breedin g values for body weight decreased for births from 1971 to 1981 then rapidl y increased for later births in all lines.