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Estimation of Genetic Parameters in a Crossbred Population of Black and White Dairy Cattle

Department of Animal Breeding, Wageningen Agricultural University, PO Box 338, Wageningen, The Netherlands

ABSTRACT

Genetic parameters were estimated using data of cows with variable proportions of genes from two breeds: Dutch Friesian and Holstein-Friesian. The data set contained 92,333 first lactation records (305-d milk production) from 675 young sires and 307,050 records from 202 proven sires.

Data were analyzed using four additive mixed models with genetic groups defined according to 1) breed composition of the cow, 2) breed composition of sire and dam, 3) linear regression on the fraction and Holstein-Friesian genes of the cow, and 4) breed composition of sire. A nonadditive model included a linear regression on breed fraction, heterozygosity, and recombination in the cow's genome.

Estimates for heterosis varied from 2.5% (fat yield) to 0% (protein percentage). Recombination effects varied from –1.9% (protein yield) to 1.5% (fat percentage). Additive models with progeny groups overestimated genetic variance by 6%. Models with sire groups overestimated additive genetic values of imported Holstein-Friesian sires by 33%. Using a nonadditive model, heritability estimates were .38 for milk yield, .80 for fat percentage, and .70 for protein percentage. It was concluded that a nonadditive model was preferable for estimation of genetic variance and prediction of breeding values in crossbred dairy populations.

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