Interleukin-2 ((IL-2) gene polymorphism and association with heat tolerance in Nigerian goats

- The IL-2 sequence of Nigeria indigenous goats was similar to the referenced orthologous sequence.
- The phylogenetic trees revealed largely species-wise clustering, while the RS and SH goats were closer compared to the WAD goats.
- The heterozygote (TA) had a comparative advantage over the homozygote (AA) in terms of rectal temperature.
- The SH goats also displayed greater resistance to thermal stress compared to the RS and WAD goats.
- Varying sex and interaction effects on the thermal indices may find application in the selection of superior animals for resistance to heat stress.

Interleukin-2 (IL-2) serves as a potent immuno-modulator, and plays a unique role in both the activation and maintenance of immune responses and in lymphocyte development. Gene polymorphism in IL-2 gene in three major Nigerian goat breeds [West African Dwarf (WAD), Red Sokoto (RS) and Sahel (SH)] was analysed by restriction fragment length polymorphisms (RFLP). The restriction enzyme, DraI was utilized. The association between the polymorphic site and some heat tolerant traits were also investigated in a total of 157 animals comprising 59 WAD, 69 RS, and 29 SH goats of both sexes. The IL-2 sequence displayed a 98% nucleotide identity with the referenced Cahi-IL-2 AY603404.1 orthologous sequence in GenBank. The phylogenetic trees revealed largely species-wise clustering, while the RS and SH goats were closer compared to the WAD goats. DraI genotype frequencies were in Hardy-Weinberg Equilibrium (P < 0.05). The expected heterozygosity (H), which is a measure of gene diversity in the goat populations, ranged from 0.26 to 0.28. The heterozygote (TA) had a comparative advantage over the homozygote (AA) in terms of rectal temperature (39.21 ± 0.08 (TT) and 38.86 ± 0.13 (TA); P < 0.05). The SH goats also displayed greater resistance to thermal stress compared to the RS and WAD goats. There were varying sex and interaction effects on the thermal indices. The present findings may find application in the selection of superior animals for resistance to heat stress as well as provide insight to questions about evolution, ecology and conservation of Nigeria indigenous goats.