Trends in Breeding Value and Production

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Abstract
Over 3.6 million first lactation records by cows on official test were studied. About 15.5 yr of data for 6 dairy breeds were represented. Sire breeding value was twice the sire''s Modified Contemporary Deviation from the USDA Sire Summary. Sire breeding values for milk and fat of cows calving in the later years increased for all breeds but Ayrshires, which were essentially static. Annual trends in sire breeding values for kg milk in the breeds over 1968-1975 were Ayrshire 7, Guernsey 26, Holstein 38, Jersey 65, Brown Swiss 80 and Milking Shorthorn 58. The corresponding trends of estimated breeding values of 1st-lactation cows were 16, 20, 21, 34, 45 and 38 kg. Superiority in breeding values for artificial insemination sires over other sires ranged from 230-580 kg of milk and 6.6-23.5 kg of fat among breeds in 1974, the last complete year of data. The amount of superiority was increasing. Annual changes in management were estimated by the total change minus the change in cow genetic merit. The annual changes in management and genetics showed that in recent years more improvement was due to genetics. With improved genetic evaluation procedures and likely continued economic restrictions on feed input, breeding is expected to continue to increase in importance for improved yields.

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