International genetic evaluations in cattle allow comparing animals’ estimated breeding values between two or more countries. Genetic correlations are among the key inputs of international evaluations and they define how much the information of relatives recorded in one country contribute to the estimated breeding value of an animal in another country. Researchers of Wageningen University & Research investigated the impact of a particular type of genetic correlations called 'direct-maternal genetic correlations' on international estimated breeding values. Their results have been published in the Journal of Animal Science.
Maternally influenced traits
In beef cattle, the individual phenotypic expression of some traits is influenced by the abilities of its mother. For instance, the observed weaning weight of a calf is influenced by its mother’s milk production and maternal care from gestation up to the weaning day. These maternal abilities create similarities within the same families and variations between different families. Therefore, the genetic evaluations of maternally affected traits need to account for these maternal influences when animals’ breeding values are estimated. This is usually done by including into the genetic model a 'maternal genetic effect'. Next to it, breeders also model the genetic correlation between the animal’s so-called 'direct genetic effect' and the maternal genetic effect. This correlation is called 'direct-maternal genetic correlation'.
Direct-maternal genetic correlations in international evaluations
In international evaluations of maternally influenced traits, the direct-maternal genetic correlation (rdm) need to be estimated and modelled both at the national level, i.e. within the same country (rdm_WC), and at the international level, i.e. between countries (rdm_BC). However, estimating the rdm_BC is particularly challenging and, therefore, these correlations are currently assumed to be equal to zero. Therefore, the rdm_BC are ignored in the international model when computing animals’ international estimated breeding values (IEBVs). Researchers at WUR investigated the impact of this assumption for rdm_BC on IEBVs using more than 3 million records for weaning weight (a maternally affected trait) from 10 European Limousin beef cattle populations. Moreover, researchers also investigated the possible impact of assuming rdm_WC to be equal to zero on IEBV, although this is not the current practice in international evaluations. In the analysed dataset, researchers showed that the current assumption for rdm_BC has a limited impact on the IEBVs while modelling rdm_WC to be equal to 0 would impact the IEBVs. The insights of this research increase our understanding of how direct-maternal genetic correlations impact the IEBVs and contribute to outlining guidelines for estimating genetic correlations between countries in international evaluations.
International evaluations of beef cattle
Farmers seek to use the best bulls available to genetically improve their herds. The international organization called 'Interbeef' offers third-party international evaluations of beef cattle since 2006 and allows to compare national and foreign sires by computing international estimated breeding values. Interbeef evaluations allow farmers to choose from a larger panel of elite bulls to better meet their selection objectives. Currently, Interbeef collaborates with 15 countries worldwide and delivers genetic evaluations for 5 different breeds (Limousin, Charolais, Hereford, Simmental, and Angus) and 3 traits (weaning weight, calving ease, and birth weight).