Genetic Diversity Of The Bovine Leukocyte Antigen (Bola) And Its Association With Resistance To Ticks And Tick-Borne Diseases In Selected Beef Cattle Breeds In Namibia

ABSTRACT

The bovine leukocyte antigen (BoLA) class II genes play a significant role in presenting processed peptides to CD4 + T lymphocytes. BoLA genes particularly class II are highly polymorphic, enhancing the number of peptides that an individual can recognise thereby triggering a cascade of immune responses. This study investigated the genetic diversity of the BoLA class II genes in 249 animals comprising of Nguni ecotypes, Bonsmara and Afrikaner cattle from Khomas, Omusati and Zambezi regions in Namibia. Molecular characterisation of the three cattle breeds was performed using four microsatellite markers (DRB3, DRBP1, RM185, BM1815) within the BoLA genes, or in close proximity, to assess genetic diversity and to determine the population structure. Ticks infesting the animals naturally were counted and identified. In addition, animals were screened for tick-borne infections (Anaplasma/ Ehrlichia and Babesia/ Theileria) using “catch-all” primers for Anaplasma/ Ehrlichia and Babesia/ Theileria cluster of species. A total of thirty seven alleles were identified across all breeds. Nguni cattle exhibited the highest level of genetic diversity (He = 0.728) and Bonsmara cattle had the lowest level of genetic diversity (He = 0.637). Extensive inbreeding (FIS = 0.247) was observed in Afrikaner cattle while Bonsmara cattle showed evidence of outbreeding (-0.057). The Bayesian cluster at K = 3 revealed genetic admixture between breeds. The overall Anaplasma/ Ehrlichia and Babesia/ Theileria infection prevalence across all breeds was 85% and 53%, respectively. Ticks infesting the animals included species (relative prevalence) of Hyalomma truncatum (35%), Hyalomma turanicum (2%), Hyalomma rufipes (29%), Rhipicephalus evertsi evertsi (5%), Rhipicephalus evertsi mimeticus (9.5%), Rhipicephalus simus (16%), Rhipicephaluss appendiculatus (3%) and Amblyomma variegatum (0.5%). Alleles associated with tick and tick-borne disease resistance were identified. Alleles DRB3-289, DRB3-290, DRB3-291, DRB3-292, RM185-93 and BM1815-145 were associated with tick and tick resistance were identified. Allele DRB3-290, DRBP1-120, DRBP1-122 and DRBP1-126 were associated with decreased incidence of Anaplasma/Ehrlichia infections in Namibian cattle breeds. Significant allelic association (P ˂ 0.15) was found between three DRBP1 alleles (DRPB1-122, DRBP1-124, DRBP1-128), four alleles belonging to the RM185 locus (RM185-101, RM185-103, RM185-105, RM185-107) and resistance to Babesia/Theileria infections. These alleles can be used as potential markers for the selection of cattle with tick and tick-borne disease resistance. The results of this study can aid in future marker-assisted selection (MAS) in breeding programs for animals with superior tick and tick-borne disease resistance.