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Estimation of Direct and Maternal Additive and Heterotic Effects from Crossbreeding Experiments in Animals¹

North Carolina State University, Raleigh 27650

Abstract

A model is proposed for the estimation of genetic effects from crossbreeding data. Analyses of variance and appropriate F-tests allow estimation of the importance of various effects. Deviations from the model provide evidence about the existence of epistasis and(or) linkage effects. This procedure has three advantages over conventional analyses of crossbreeding data: (1) It is a less complex statistical procedure; (2) It provides a clearer understanding of the genetic components; (3) It allows prediction of breed crosses that were not included in the data set. This model was applied to data from the long-term dairy crossbreeding project conducted at the Beltsville Agricultural Research Center. Breed additive genetic superiorities of Holsteins over Ayrshires and Brown Swiss were 759 and 857 kg for milk yield (P<.01), 555 and 556 kg for fat-corrected milk yield (P<.05) and —.30 and —.44 for fat percentage (P<.01), respectively. Differences between Brown Swiss and Ayrshires were small. The nonadditive genetic effects measured by regression on the expected percentage of heterozygotic loci were important for Brown Swiss x Holstein and Ayrshire x Holstein crosses. Complete Brown Swiss x Holstein heterozygosity resulted in increases of 341 kg in milk (P<.05), 16.2 kg in milk fat (P<.01) and 378 kg in fat-corrected milk (P<.05). For Ayrshire x Holstein crosses, the heterosis contributions for milk fat and fat-corrected milk (P<.05) were 13.6 and 299 kg, respectively. Holstein maternal contributions for production traits exceeded those for Ayrshires and Brown Swiss by 607 (P<.01) and 476 kg (P<.01) for milk yield, 16.9 (P<.05) and 12.1 kg (NS) for fat yield and 494 (P<.01) and 375 kg (P<.05) for fat-corrected milk yield, but were .17 (P<.05) and .15% (NS) lower for fat percentage. There was no evidence that epistasis and linkage contributed significantly to differences among breed groups.

¹ Paper No. 6312 of the Journal Ser. of the North Carolina Agr. Research Service, Raleigh.

² Dept of Anim. Sci.

³ Present address: Universidad del Zulia, Facultad de Agronomia, Institute de Investigacion, Maracaibo, Venezuela.

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