Scientists discover genes that make Sudanese cattle more resistant to disease
Scientists have found unique gene variants in popular Sudanese cattle breeds that seem to make them more resistant to disease, and the discovery could lead to improved breeding strategies.
Variations in genes, called alleles, are often responsible for unique characteristics like the hardiness seen in individual animals or plants. Three breeds of cattle, Baggara, Butana and Kenana, are well-known for being resilient, and are kept by herders across Sudan for meat and milk. Studies on cattle breeds outside of Africa show that different alleles of a gene called BoLA-DRB3, which plays a role in the immune system, might make the animals resistant to disease or parasites. But until now, scientists knew very little about variations in this gene in African cattle breeds.
In this study, researchers investigated BoLA-DRB3 in Sudanese cattle, to find out whether the animals have any unique alleles that might explain their disease resistance and provide insight into these breeds for future studies.
The researchers collected blood from 225 animals across Sudan. They then conducted a genetic analysis of the samples, testing for variations in the BoLA-DRB3 gene. They then compared their findings to existing information about the gene in other cattle. They also looked at how often different alleles appeared in their samples, to try and find out why any changes might be occurring.
Overall, the Sudanese cows had many variants of the BoLA-DRB3 gene that the researchers think may boost their immune response and make them more resistant to disease. The researchers found seven alleles that were new and unique to the Sudanese breeds. They also discovered that, when compared to cattle from other parts of the world, their samples included 14 alleles of the BoLA-DRB3 gene that weren’t shared by non-African animals. These unique characteristics might help Sudanese cattle survive the combination of diseases and physical stressors, like heat, common in their environment.
The study provides the first in-depth look at genetic diversity in the BoLA-DRB3 gene in African cattle. The new alleles found also open the door for future research into disease-resistance in cattle, and how breeding programs can be improved.
An important point for future research is the exact role the new alleles play in the immune response of the cattle. While some changes increase disease resistance, others might make the animals more susceptible to certain illnesses. Future studies will therefore need to investigate the relationship between different alleles and cattle diseases.
As the first of its kind in Africa, the study is an important milestone for research into the BoLA-DRB3 gene and immune function.
Scientists from Sudan, Lebanon, Saudi Arabia, Japan and Argentina worked together on this project.
Autochthonous Sudanese cattle breeds, namely Baggara for beef and Butana and Kenana for dairy, are characterized by their adaptive characteristics and high performance in hot and dry agro-ecosystems. They are thus used largely by nomadic and semi-nomadic pastoralists. We analyzed the diversity and genetic structure of the BoLA-DRB3 gene, a genetic locus linked to the immune response, for the indigenous cattle of Sudan and in the context of the global cattle repository. Blood samples (n = 225) were taken from three indigenous breeds (Baggara; n = 113, Butana; n = 60 and Kenana; n = 52) distributed across six regions of Sudan. Nucleotide sequences were genotyped using the sequence-based typing method. We describe 53 alleles, including seven novel alleles. Principal component analysis (PCA) of the protein pockets implicated in the antigen-binding function of the MHC complex revealed that pockets 4 and 9 (respectively) differentiate Kenana-Baggara and Kenana-Butana breeds from other breeds. Venn analysis of Sudanese, Southeast Asian, European and American cattle breeds with 115 alleles showed 14 were unique to Sudanese breeds. Gene frequency distributions of Baggara cattle showed an even distribution suggesting balancing selection, while the selection index (ω) revealed the presence of diversifying selection in several amino acid sites along the BoLA-DRB3 exon 2 of these native breeds. The results of several PCA were in agreement with clustering patterns observed on the neighbor joining (NJ) trees. These results provide insight into their high survival rate for different tropical diseases and their reproductive capacity in Sudan's harsh environment.
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