Assessing Genetic Variation and Phylogenetic Relationship of Dairy Cattle Breeds Reared in Tanga Region, Tanzania Using HSF1 and HSPA6 Genes Responsible for Heat Tolerance

The objectives of this study were to determine the genetic variation and phylogenetic relationships of Holstein Friesian, Jersey and Ayrshire crossbred dairy cows and Zebu cattle reared in the humid coastal region of Tanzania based on the HSF1 and HSPA6 genes responsible for heat tolerance. The animals used in the study were obtained from Tanzania Livestock Research Institute (TALIRI) - Tanga and Livestock Training Agency (LITA) Buhuri dairy farms located in Tanga districts and Mruazi Heifer Breeding Unit dairy farm located in Korogwe district. Sixty - five blood samples were collected from Holstein Friesian (23), Ayrshire (15), Jersey (12) crosses, and pure Zebu (15). For each animal, 10 ml of blood was collected by Jugular vein puncture. Total genomic DNA was extracted and amplification performed following manufacturer’s instructions. The polymorphic sites, haplotype diversity (Hd), nucleotide diversity (π), expected heterozygosity (He) and neutrality (FU’s FS and Tajima’s D) tests were calculated. The He was 0.23 ± 0.13, 0.22 ± 0.14, 0.16 ± 0.13, and 0.00 ± 0.00 in Zebu, Holstein Friesian crosses, Jersey crosses and Ayrshire crosses, respectively. The zebu had the highest Hd (0.47 ± 0.08) followed by Holstein Friesian (0.34 ± 0.14), and Jersey (0.33 ± 0.21), while the lowest Hd was observed in Ayrshire crosses (0.00 ± 0.00). The average π was 0.23 ± 0.14, 0.22 ± 0.13, 0.16 ± 0.11, and 0.00 ± 0.00 for Zebu, Holstein Friesian crosses, Jersey crosses and Ayrshire crosses, respectively. Dairy cattle breeds were grouped in one and three clusters based on HSPA6 and HSF1 genes, respectively. There is low genetic diversity and no significant genetic differentiation among the four dairy cattle breeds, an indication of a single panmictic population.