Assessing the impact of natural service bulls and genotype by environment interactions on genetic gain and inbreeding in organic dairy cattle genomic breeding programs

摘要

The objective of the present study was to compare genetic gain and inbreeding coefficients of dairy cattle in organic breeding program designs by applying stochastic simulations. Evaluated breeding strategies were: (i) selecting bulls from conventional breeding programs, and taking into account genotype by environment (0 x E) interactions, (ii) selecting genotyped bulls within the organic environment for artificial insemination (Al) programs and (Hi) selecting genotyped natural service bulls within organic herds. The simulated conventional population comprised 148 800 cows from 2976 herds with an average herd size of 50 cows per herd, and 1200 cows were assigned to 60 organic herds. In a young bull program, selection criteria of young bulls in bothproduction systems (conventional and organic) were either 'conventional' estimated breeding values (EBV) or genomic estimated breeding values (GEBV) for two traits with low (h~2 = 0.05) and moderate heritability (h~2 = 0.30). GEBV were calculated for different accuracies (r_(mg)), and GxE interactions were considered by modifying originally simulated true breeding values in the range from r_g = 0.5 to hO. For both traits (h~2 = 0.05 and 0.30) and 0.8, genomic selection of bulls directly in the organic population and using selected bulls via Al revealed higher genetic gain than selecting young bulls in the larger conventional population based on EBV; also without the existence of GxE interactions. Only for pronounced G x E interactions (r_g = 0.5), andfor highly accurate GEBV for natural service bulls (r_(mg)> 0.9), results suggests the use of genotyped organic natural service bulls instead of implementing an Al program. Inbreeding coefficients of selected bulls and their offspring were generally lower when basing selection decisions for young bulls on GEBV compared with selection strategies based on pedigree indices.