The profile of HSPA1A gene expression and its association with heat tolerance in crossbred cattle and the tropically adapted dwarf Vechur and Kasaragod

Certain livestock breeds are adapted to hot and humid environments, and these breeds have genetics that could be useful in a changing climate. The expression of several genes has been identified as a useful biomarker for heat stress. In this study, the responses to heat exposure of heat-tolerant Vechur and Kasaragod cattle found in Kerala state in India (also known as dwarf Bos taurus indicus) were compared to crossbred cattle (crosses of Bos t. taurus with Bos t. indicus). At various time points during heat exposure, rectal temperature and the expression of HSPA1A were determined, and the relationship between them was characterized. We characterized HSPA1A mRNA in Vechur cattle and performed molecular clock analysis. The expression of HSPA1A between the lineages and at different temperature humidity index (THI) was significant. There were significant differences between the expression profiles of HSPA1A in Kasaragod and crossbred (p < 0.01) and Vechur and crossbred (p < 0.01) cattle, but no significant difference in expression was observed between Vechur and Kasaragod cattle. The ge-netic distance between Vechur, B. grunniens, B. t. taurus, and B. t. indicus was 0.0233, 0.0059, and 0.007, respectively. The genetic distance between Vechur and the Indian dwarf breed Malnad Gidda was 0.0081. A molecular clock analysis revealed divergent adaptive evolution of Vechur cattle to B. t. taurus, with adaptations to the high temperatures and humidity that are prevalent in their breeding tract in Kerala, India. These results could also prove useful in selecting heat-tolerant animals using HSPA1A as a marker.