J. Dairy Sci. 87:1506–1518 American Dairy Science Association, 2004. Genetic Parameters and Trends in the Chilean Multibreed Dairy Cattle Population*

Estimates of additive and nonadditive multibreed co-variance components, genetic parameters, and pre-dicted genetic values for first lactation 305-d mature equivalent (ME) milk yield, fat yield, and protein yield were computed using data from a sample of 3316 cows from the ChileanHolstein-other breedsmultibreed pop-ulation. Variances and covariances were estimated by 2-trait REML analyses using a Generalized Expecta-tion-Maximization algorithm applied to multibreed populations. Multiple estimates of additive genetic, nonadditive genetic, and environmental variances from 2-trait analyseswere averaged to yield a single variance estimate for each trait and effect. Heritabilities were moderate for all traits in Holstein, other, and Holstein × other crossbred groups. Interbreed interactibilities (ratio of nonadditive genetic to phenotypic variances) were all near zero. Multibreed additive, nonadditive, and total genetic trends were estimated using the com-plete dataset (56,277 cows). Upward trends between 1990 and 2000 existed for all traits, genetic effects, and breed groups, except for 305-d ME protein yield in ⁄ Holstein, indicating that Chilean dairy producers were successful in choosing progressively better semen and sires from imported and local sources over time. (Key words: genetic parameter, genetic trend, multibreed, upgrading) Abbreviation key: H = Holstein, H/O = intralocus Holstein/other breeds, FY = 305-d mature equivalent fat yield,ME =mature equivalent,MPTA =multibreed PTA,MREMLEM=multibreedREMLusing a general-ized expectation-maximization algorithm, MY = 305-d mature equivalent milk yield, O = other breeds, PY = 305-d mature equivalent protein yield