Genetic Trends in Milk Production in Florida Dairy Herd Improvement Association Herds

First-lactation records of 4,779 Holstein, Jersey, and Guernsey paternal halfsisters, representing 155 sires and 181 herds for 1958 to 1967, were subjected to a series of least-squares analyses. Average age at freshening was 27.4, 26.4, and 29.5 months for the three breeds. Average production was 4,712 kg milk, 3.70% fat, and 173 kg fat for Holsteins and average productions for Jerseys and Guernseys were 3,144 kg, 4.99%, 156 kg, and 3,227 kg, 4.57%, and 147 kg. Estimates of trends were from weighted regressions of least-squares year constants on years, with and without sire in the mathematical model. Annual genetic trends were for Holsteins: 33 kg milk, --.034% fat and --.7 kg fat; for Jerseys, 22 kg, .008% and 1.3 kg; for Guernseys, 92 kg, --.048% and 2.8 kg. Environmental trends for milk yield were positive for Holsteins (57 kg) but negative for Jerseys and Guernseys (10 kg and 23 kg).