A Sigurdsson

Estimation of Genetic (Co)variance Components for International Evaluation of Dairy Bulls

Abstract Within- and across-country genetic parameters need to be estimated prior to an international genetic evaluation of dairy bulls. A procedure based on the Expectation Maximization algorithm to produce restricted maximum likelihood estimates of such parameters, using national evaluation results from different countries, was tested by simulation. Individual performance records were generated for two populations of dairy cattle with separate breeding programmes but considerable genetic exchange to create ties between the populations. A genotype-by-country interaction effect was generated by simulating the data according to a genetic correlation of 90 between performance in the two countries. Within-country national evaluations were computed with animal models. The estimation procedure was tested using bull national evaluation results. The impact of factors such as data connectedness, time period, and bias in national evaluations on estimated parameters was investigated. When all data were included in ...

Dependent Variables in International Sire Evaluations

Abstract Stochastic simulation was used to assess the suitability of alternative dependent variables in international sire evaluation. Three such variables were considered: daughter yield deviations (DYD), national proofs (ETA), and de-regressed national proofs (DPRF). Data from two dairy cattle populations considering 10 generations were simulated. Genetic ties necessary for a joint evaluation of the two populations were established with bull exchange in each generation. De-regressed national proofs were the best and ETA were the worst in estimating genetic difference between the two populations and ranking bulls across country. Further, de-regressed national proofs can be easily computed and, contrary to DYD, are always available. De-regressed national proofs are recommended as dependent variables in across country sire evaluation.

Predicting Genetic Trend by Uni- and Multitrait Models

Abstract The effects of evaluating milk yield in the first three lactations by a single-trait animal model or by a repeatability animal model instead of by the true multitrait animal model were investigated using stochastic simulation. The models were compared both in terms of how accurately they predicted genetic trend when applied to the same dataset and regarding difference in true genetic progress when selecting on breeding values predicted by these models. A breeding structure resembling the Icelandic dairy cattle population was used for the simulation. The single-trait model underpredicted the true genetic trend in second and third lactations quite heavily but only by 2.3% in the first lactation, while the repeatability model overpredicted the true genetic trend in the first three lactations by 9.4% on average. The multitrait animal model, however, estimated genetic trends with a high degree of accuracy. When selection was made on all three lactations with equal economic weights, the multitrait mode...

Inbreeding and Its Impact in the Closed Population of Icelandic Dairy Cattle

Abstract Average inbreeding coefficients were calculated for the Icelandic dairy cattle population, using pedigree records of 129 115 animals with the most remote ancestor born in 1902 and the youngest animals born in 1991. The average coefficient for animals born 1980 or later and with at least both parents and one grandparent known was 1.82%, but for animals with at least four ancestral generations known it was 2.70%. No significant trend in inbreeding was detected in the period after 1980 when considering animals with at least four ancestral generations known. The AI bulls were inbred by 2.39% on average and a significant increase in inbreeding of +0.08% per year was detected. The effects of inbreeding level on milk, fat and protein yields in each of the first three lactations were estimated by including inbreeding level in the multitrait animal model currently used for breeding value estimation of the breed. A large proportion (58.6%) of the cows with production records were inbred. Negative effects w...

Estimation of Genetic and Phenotypic Parameters for Production Traits of Icelandic Dairy Cattle

Abstract Heritabilities, genetic and phenotypic correlations among yields of milk, fat and protein, fat percentages and protein percentages were estimated using a sire model and multivariate REML for 15357 first-lactation records of the Icelandic dairy cow. These heifers were daughters of 136 young and 55 proven Icelandic bulls. Proven sires were treated as fixed effects and did not contribute to the inter-sire variance. Heritabilities for milk, fat and protein yields and fat and protein percentages were 0.23, 0.17, 0.18, 0.18 and 0.37, respectively. Variance and covariance components were estimated for the same traits, using the first three lactations of 5705 daughters of 138 bulls. Heritabilities for milk yield in the first three lactations were 0.17, 0.12 and 0.10, for fat yield 0.17, 0.10 and 0.09 and for protein yield 0.14, 0.11 and 0.11. Genetic correlation was 0.76 between milk yield in first and second lactation and 0.66 between first and third lactation. Genetic correlations for fat and protein y...