Abstract

To accurately predict breeding values, genetic evalu- ations must define an appropriate model that considers the main factors influencing the traits of interest. The challenge increases in crossbreeding populations, such as those found in Chile, where multiple breeds, includ- ing those from different countries, are used. In particu- lar, the country of origin is not currently incorporated into genetic models used in Chile. The objectives of this study were 2-fold: specialIntscript to evaluate different genetic models of increasing complexity to determine if the in- clusion of a specific strain classification, strain propor- tions in crossbred animals , heterosis effects could enhance genetic evaluations compared with the current model used in Chile; , specialIntscript to determine the presence of heterosis effects among specific dairy genetic strains when crossed with Chilean Friesian cows, focusing on annual milk, fat, and protein production; SCS; and calv- ing interval. A dataset of 1,429,132 records from 586,624 cows that calved between 1998 and 2018 was provided by the Chilean Agricultural and Services Cooperative (COOPRINSEM; Osorno, Chile). Using pedigree in- formation, the proportion of each cattle breed accord- ing to its different countries of origin (genetic strain) was calculated for each animal. Subsequently, strains concerning Chilean Friesian cows were selected with a wide range of proportions. The final dataset included 8 strains: Chilean Friesian, French Holstein-Friesian, US-Holstein, US-Jersey, French Montb & eacute;liarde, New Zealand Holstein-Friesian, Swedish Red and White, and British Friesian, representing 369,755 observations collected between 2009 , 2018. Production (milk, fat , protein production per lactation) and functional traits (SCS and calving interval) were also provided by COOPRINSEM. Four different models were tested: the current model using only 5 breed categories based on physical appearance (M1), a more precise classification considering 8 dairy strains categories (M2), M2 plus the inclusion of a cross-classified effect of crossbreeding proportion with strain categories (M3), and M3 plus the cross-classified effect of heterosis level with strain categories (M4). Our results show that M4 was the best model for analyzing information on crossbred dairy cows from Chile. Our study also suggests that there are specific effects for some strains, as well as heterosis ef- fects between several strains and the Chilean Friesian.