Role of genetic introgression in introducing mutant alleles in Bos indicus cattle and prevalence of lethal genetic disorders in Bos taurus × Bos indicus and Bos indicus cattle in India.

Fertility is an important trait associated with reproductive performance and animal welfare concern. Lethal alleles affect fertility through early embryonic death, abortions, and stillbirth depending on the genetic expression of the allele. Holstein Friesian and Jersey are two major Bos taurus breeds used widely for increasing milk yield along with purebreds of Bos indicus breeds like Gir, Kankrej, Sahiwal, and Tharparkar. In the present study, prevalence of lethal mutants in crossbred Holstein Friesian (CBHF, n = 2435), crossbred Jersey (CBJY, n = 2874), Gir (n = 3288), Kankrej (n = 593), Sahiwal (n = 965), and Tharparkar (n = 18) were studied. Heterozygous carrier animals were identified for bovine leukocyte adhesion deficiency (BLAD), Citrullinemia, complex vertebral malformation (CVM), Brachyspina, Holstein Haplotype 1 (HH1), Holstein Haplotype 3 (HH3),Holstein Haplotype 4 (HH4) and Jersey Haplotype 1 (JH1). Breed purity analysis confirmed inheritance of Bos taurus genes contributing to the presence of lethal mutant alleles like BLAD, Citrullinemia, HH1, and JH1 in apparently phenotypic Bos indicus animals. Screening and elimination of heterozygous carrier bulls/cows is essential to control fertility loss associated with lethal alleles.