Abstract
The 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 follicle samples from sixty calves (6 months old; 30 Korean native beef calves and 30 Holstein dairy calves) were collected for DNA extraction. The HSP70 single nucleotide polymorphism (SNP) was genotyped using a 5'-exonuclease activity (TaqMan) assay. In Study 1, PBMCs were isolated from 20 calves categorized by their HSP70 genotypes during a thermoneutral period: 10 Korean native beef calves (B-CC and B-C/-type) and 10 Holstein dairy calves (D-CC, D-C/-type). The PBMCs were then exposed to heat stress at 37 °C (control, CON) and 42 °C (heat stress, HS) for 3 h. Following this, the cells were returned to the 37 °C incubator at 0, 1, 3, 6, and 12 h for further recovery analysis. In Study 2, hair follicles were collected from 20 calves (six times every 30 days; threshold, mild, and moderate stress levels) and HSP70 gene expression was measured. Data were analyzed via two-way analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) test. The cell proliferation in the D-C/-group was significantly higher (p < 0.05) than in the D-CC and B-C/-groups at 0 and 1 h after HS for 3 h. The mRNA gene expression of HSP70 was greater (p < 0.01) in all HS groups compared to the CON groups after heat exposure. The expression of the HSP70 gene in the D-C/-group was significantly higher (p < 0.05) compared to the B-CC and B-C/-groups immediately (0 h) following 3 h of HS. The expression in the D-CC group also higher (p < 0.05) than in the B-C/-group. The gene expression of HSP70 in hair follicles increased more at the moderate HS level than that at the threshold level. In addition, overexpression of HSP70 was noted (p < 0.05) in the D-CC and D-C/-groups compared to the B-CC and B-C/-groups. In conclusion, our results indicate that breeds and HSP70 genetic polymorphisms exhibit a distinctive pattern of immune cell proliferation and HSP70 expression profiles. Additionally, the HSP70 gene expression in hair follicles may serve as an indicator of heat resistance across different breeds, making it a potential novel barometer for HS.