PhD defence Renzo Bonifazi on international genetic and genomic evaluations of beef cattle

His thesis aimed to improve and further develop
methodologies for international beef cattle evaluations (Interbeef) by
addressing various challenges related to: 1) the estimation of across-country
genetic correlations and their impact on the international estimated breeding
values (EBV_INT), 2) the inclusion of national genomic information,
and 3) the development of an official procedure for participating countries to
integrate the distributed EBV_INT back into their national
evaluations.

Improving international beef cattle evaluations

Advancements in reproductive technologies (for example artificial insemination) allow the exchange of genetic material of elite bulls across countries. Therefore, breeders can better meet their selection objective by accessing top foreign bulls for traits of both economic and societal relevance, such as the animal’s carcass weight, feeding efficiency, or methane emissions. However, differences in environmental characteristics and trait definitions between countries make the ranking of top bulls in one country different from that of another country. To help breeders accurately rank top bulls across different countries, evaluations that combine data from different countries – also called international evaluations – have been developed. In his thesis, Renzo addressed several challenges currently faced by Interbeef to improve and develop the current evaluations further.

The overall thesis objective focused on the three abovementioned aspects of beef cattle international evaluations. In the first part of his thesis, Renzo showed that both large and small participating countries benefit from current Interbeef pedigree-based evaluations. He then showed the feasibility of estimating across-country genetic correlations using a multi-trait approach that simultaneously fits data from all countries and proposed data sub-setting strategies to improve the associated computational time. Third, he showed that the current practice of assuming across-country direct-maternal genetic correlations to be 0 has a limited impact on the EBV_INT of animals of interest, such as publishable sires (in other words, sires that meet Interbeef publications rules). On the other hand, assuming zero within-country direct-maternal genetic correlations impact the EBV_INT of such animals. Fourth, he developed international genomic evaluations for beef cattle using a single-step SNPBLUP approach (ssSNPBLUP). International ssSNPBLUP evaluations lead to higher accuracies than current international pedigree-based evaluations and either national pedigree-based or genomic evaluations while keeping similar or slightly reduced level and dispersion bias. Finally, he developed a generalized and easy-to-implement procedure to integrate pedigree-based or genomic EBV_INT of publishable sires into national evaluations.

Compared to national evaluations without integration, the integration procedure reduces level bias, keeps similar dispersion, and increases the accuracies of publishable sires’ EBV_INT.

Since June 2022, Renzo works as a researcher at Wageningen Livestock Research (Wageningen University & Research).

The research described in this thesis was financially supported by the Interbeef Working Group, the International Committee for Animal Recording—ICAR (Rome, Italy), the International Bull Evaluation Service (Uppsala, Sweden), and the Irish Cattle Breeding Federation (ICBF, Link Road, Ballincollig, Co. Cork, Ireland).