Characterization and identification of novel polymorphisms in the OR51H1 gene associated with resistance/tolerance to natural Theileria infection in Vechur (Bos indicus) and crossbred (B. taurus × B. indicus) cattle in a Theileria-endemic region.

Theileriosis is a haemo protozoan disease affecting livestock, causing high mortality and production loss. Although therapeutic and vector control measures are available, selecting Theileria-resistant/tolerant animals is considered an alternate control measure for which the identification of genetic markers is essential. The present study screened dwarf Vechur (Bos indicus) and crossbred (B. taurus × B. indicus) cattle for natural infection to Theileria using peripheral blood smear and clinical and haematology evaluation. Polymorphisms in a previously identified candidate gene were screened in olfactory receptor family 51 sub-family H member-1 (OR51H1, single exon, 948 bp) associated with Theileria tolerance. The association of Theileria resistance/tolerance with different genotypes was also evaluated. Theileria was detected in 32.45 % of crossbred and 6 % of Vechur. Resistance and tolerance to Theileria infection varied significantly across breeds, and Vechur was found resistant (no parasites detected in the blood smear) compared to crossbred (Odds ratio-0.14, 95 % CI- 0.03-0.42, p < 0.01). The OR51H1 gene was characterised by sequencing in Vechur cattle, and putative single nucleotide variations (SNVs) were identified by pooled sample sequencing and genotyped using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism). The five SNVs, T271C, C272T, T362C, G180A and T181G, exhibited polymorphic patterns. SNVs T271C and C272T were tolerant, while T362C, G180A and T181G were non-tolerant. The population was in Hardy-Weinberg equilibrium for SNV G180A in crossbred cattle and for SNVs T271C, C272T, and G180A in Vechur cattle. The SNVs T271C in crossbred and T362C, G180A and T181G in Vechur were significantly associated with Theileria tolerance. The identified SNVs also had moderate to high heterozygosity and polymorphic information content. The findings imply that these SNVs can be used as potential markers to select Theileria-resistant Vechur and tolerant crossbred cattle using marker-assisted selection.