PSXIV-5 Evaluation of Heat Resistance in Beef and Dairy Calves Using Peripheral Blood Mononuclear Cells and Hair Follicles Based on Heat Shock Protein 70 Genetic Polymorphisms

Heat resistance depends on the breed of cattle and is important for genetic improvement under heat stress (HS). Study objectives were to investigate the heat resistance using peripheral blood mononuclear cells (PBMCs) and hair follicles in beef and dairy calves based on heat shock protein (HSP) 70 genetic polymorphisms. The hair follicles samples from sixty calves (6-month-old, 30 Hanwoo calves, and 30 Holstein calves) were collected for DNA extraction. The HSP70 genotype was analyzed based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) before the experiment. In study 1, PBMCs were isolated from 20 calves (10 Hanwoo calves; H-CC, H-C/-type, and 10 Holstein calves; D-CC, D-C/-type) and exposed to heat (37°C; Con and 42°C; HS) for 3 h. Cells were harvested and used for mRNA gene expression via RT-qPCR. Cell proliferation was measured using an ELISA kit. In study 2, hair follicles were collected from 20 calves (six times every 30 days; low-HS, medium-HS, and high-HS) and HSP70 gene expression was measured. Data were analyzed by two-way ANOVA and Tukey HSD test. Heat exposure decreased the cell proliferation rate (P < 0.05) in the D-CC and D-C/- groups compared with the H-C/C and H-C/- groups. The mRNA gene expression of HSP70 was greater (P < 0.05) in D-C/- group than in the H-CC and H-C/- groups after heat exposure. Gene expression of HSP70 of hair follicles was increased by high-HS level than those at the low-HS level. In addition, overexpression of HSP70 was noted (P < 0.05) in D-CC and D-C/- groups compared with the H-CC and H-C/- groups. Our results indicate that breeds and HSP70 genetic polymorphisms exhibit a distinctive pattern of immune cell proliferation and HSP70 profiles. The HSP70 gene expression in hair follicles can represent heat resistance in different breeds, and therefore, it can be used as a novel HS barometer.