Estimation of Genetic Trends in Dairy Cattle Populations

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Abstract
Usefulness of full sisters and paternal half-sisters to estimate genetic trends was investigated, with 34,380 1st lactation Holstein Herd Improvement Registry (HHIR) records reported in 335 herds from 1953 to 1961. Paternal half-sister families comprised 1/3 and full-sister families 1/7 of the data. All records were analyzed to obtain lease-squares constants for year of calving. A weighted regression of these constants on years provided an estimate of the annual trend, genetic plus environmental, (63[plus or minus]11 kg for milk and 0.007[plus or minus]0.001 for per cent fat). Full sisters were analyzed to obtain least-squares year constants adjusted for sire and dam effects and corrected for selection. Weighted regression of these constants on years indicated the environmental trend in the population, and comparison with the genetic plus the environmental trend provided an estimate of annual genetic trend (45[plus or minus]16 kg for milk and 0.018[plus or minus]0.003 for per cent fat). A 2nd estimate of the annual genetic trend " (55[plus or minus]26 kg for milk and 0.016[plus or minus]0.005 for per cent fat) was obtained by comparing the over-all trend with 1/2 for genetic, plus environmental trend estimated from records of paternal half-sisters adjusted for sire effects.