Associations among heat shock protein 70 genotype, forage system, and horn-fly infestation of beef cattle

The objective of this experiment was to determine the relationships among cattle breed, heat shock protein 70 (Hsp70) genotype, and horn-fly density. Angus (n = 20), Brahman (n = 17), and reciprocal cross (n = 31) spring-born cows were assigned to 1 of 2 permanent forage types: wild-type endophyte-infected tall fescue [Lolium arundinaceum (Shreb.)] or common bermudagrass [Cynodon dactylon (L.) Pers]. Individual fly density was determined weekly at a distance of 5 to 10 m from May to October. Genomic DNA was prepared from buffy coat and purified. Specific forward and reverse PCR primers were used to produce Hsp70 amplicons of the coding (G2033C) and promoter (C895D and G1128T) regions. Each amplicon was sequenced, and genotypes were assigned to each single nucleotide polymorphism (SNP) site. Horn-fly density was affected (P < 0.0001) through a forage type-by-month interaction. In September, cattle grazing tall fescue had fewer flies (P < 0.05) than did cattle grazing bermudagrass. Heterozygous cows at the coding sequence SNP G2033C had more (P < 0.07) flies than did homozygous cows. Comparatively, cows heterozygous for either of the 2 promoter region SNP tended to have greater (P < 0.10) fly density than did those homozygous. Use of Hsp70 genotyping in combination with forage could be useful in identifying production systems that decrease horn-fly infestation.