Genetic diversity of BoLA-DRB3 and its association with Anaplasma marginale and Babesia spp. infections in creole cattle of northeastern Colombia.

The BoLA-DRB3 gene is one of the most polymorphic loci in cattle, with alleles associated with susceptibility or resistance to several infectious diseases, including leukosis, mastitis, and hemotropic infections. In this study, we assessed the genetic diversity of the BoLA-DRB3 gene in three Colombian Creole cattle breeds and examined its association with natural infections by Anaplasma marginale and Babesia spp. in northeastern Colombia. A total of 97 animals (Chino - CrChi, n = 34; Casanareño - CrCAS-, n = 32; Sanmartinero - CrSM-, n = 31) from Arauca, Casanare, Meta, and Santander departments were genotyped using PCR-direct sequencing of the second exon of the BoLA-DRB3 gene. Overall genetic diversity was moderate, with a nucleotide diversity of π = 0.086, a mean pairwise distance of 18.97, and 62 segregating sites. Among the breeds, CrCAS showed the highest diversity, followed by CrChi and CrSM. We identified 35 BoLA-DRB3 alleles, 34 of which were previously reported in the IPD-MHC database, while one was novel. The CrChi population showed significant deviation from Hardy-Weinberg equilibrium. Two alleles, BoLA-DRB3*001:01 and BoLA-DRB3*025:01:01, were significantly associated with reduced risk of B. bigemina infection in CrSM, whereas BoLA-DRB3*048:02 was linked to increased susceptibility to B. bovis in CrChi. This study confirms the high genetic variability of Colombian Creole cattle breeds. The high frequency of alleles associated with B. bigemina infection in CrSM highlights its potential as a genetic reservoir for future studies evaluating the heritability and functionality of these alleles. In contrast, the elevated frequency of a susceptibility-associated allele for B. bovis infection in CrChi, together with evidence of inbreeding, underscores the urgent need for targeted conservation and breeding strategies to preserve genetic diversity and reduce disease vulnerability to infectious diseases in this breed.