Pilot genomic evaluations of French crossbred dairy cattle

Abstract

The use of crossbreeding in dairy cattle has been increasing, reflecting breeders’ interest in new strategies to address current challenges in the dairy industry. Crossbred animals benefit from both parental breeds abilities and from heterosis, making them attractive to producers. However, genetic tools commonly used in purebred populations, such as pedigree or genomic estimated breeding values (GEBV), are not yet available for crossbred populations, limiting herd management options and the prediction of future phenotypes. The TransEvagenoc project aimed to develop and test a genomic evaluation tool adapted to current crossbred populations. Genotypes from 4,004 individuals resulting from crosses among the three main French dairy breeds (Normande, Montbéliarde, Holstein) were used. Breed-of-origin of alleles (BOA) and heterosis percentages were estimated based on reference populations of 5,000 individuals per pure breed. SNP effects estimated in pure breeds were then applied to crossbred genotypes according to BOA, and breed differences and heterosis effects were then added to estimate breeding values. Evaluations were performed for milk, fat and protein yields (MY, FY, PY), somatic cell score (SCS) and interval from calving to first service (ICFS). Methodological choices, such as GEBV standardisation, and results preparation were discussed in focus groups (FG) with industry stakeholders to better align to the field needs. Correlations between breeding values and first-lactation phenotypes were 0.35, 0.27, 0.28, 0.31 and 0.08 for MY, FY, PY, SCS and ICFS, respectively. Based on focus group discussions, GEBV were standardised using a representative crossbred population. This tool provides a first genomic evaluation framework for the French crossbred dairy cattle encouraging the collect of additional crossbred genotypes and phenotypes.