Evidence of selection against recessive defects

H.D. Norman1, D.J. Null2and P.M. VanRaden2

1Council on Dairy Cattle Breeding, Bowie, MD 20716
2USDA, Agricultural Research Service, Animal Genomics and Improvement Laboratory, Beltsville, MD 20705-2350, USA

2022 J. Dairy Sci.


Haplotype tests are effective for differentiating animals with traits of desirable performance, or conversely, that carry recessive detrimental alleles. Our objective was to show how the frequencies of carriers have changed in US dairy animals over time. Several are haplotypes impacting fertility, first described by VanRaden. In the homozygous state, embryonic death or stillbirth occurs. When abortions occur vary, thus economic losses vary also. Semen from carrier bulls continued to be used, but their tested sons are often by-passed. Carrier frequency by year was derived from genotypes; those from 2011 and 2021 are shown; AH1 and AH2 in Ayrshires is high (18.5 to 19.9%); only slightly below 2011. BH2 in Brown Swiss is 5.7%, down 2/3rd from 2011. Several haplotypes in Holsteins have been uncovered. Carriers in 2011 & 2021 were: HH0 5.9 & 0.9; HH1 4.3 & 1.0; HH2 3.6 & 1.8; HH3 6.8 & 1.9; HH4 0.7 & 0.2; HH5 4.2 & 6.3; and HH6 0.7 & 1.9. JH1 in Jerseys were 23.3 & 9.7%. Carriers for BLAD, CVM, DUMPS, and mulefoot were 0.1, 0.6, 0.01 and 0.02 in 2021. Recently discovered JNS rose from 3.6 to 7.2%. Carriers sometimes rose prior to discovery making detection easier; after they were uncovered, selection against them followed.

Keywords: cattle, fertility, genomics, haplotypes