Hypoxia-inducible factor-1α is involved in the response to heat stress in lactating dairy cows

Hypoxia-inducible factor-1α (HIF-1α) is important in maintaining cellular oxygen homeostasis and cellular heat tolerance. To explore the role of HIF-1α in the response to heat stress (HS) in dairy cows, 16 Chinese Holstein cows (milk yield: 32 ± 4 kg/d, days in milk: 272 ± 7 d, parity: 2-3) were used to collect coccygeal vein blood and milk samples when cows were under mild (temperature-humidity index = 77) and moderate HS (temperature-humidity index = 84), respectively. Compared to cows under mild HS, the respiratory rate (P < 0.01), rectal temperature (P < 0.01), and blood concentrations of heat shock protein (HSP)70 (P < 0.01) and HSP27 (P < 0.01) were higher, but oxygen saturation (P = 0.02) and hemoglobin (P < 0.01) were lower in cows under moderate HS. Blood HIF-1α concentration was greater (P < 0.01) during moderate HS, indicating that HIF-1α is involved in lactating cows' response to HS. To confirm these findings, we collected coccygeal vein blood and milk samples from 59 dairy cows under moderate HS. The HIF-1α levels were correlated with the levels of heat shock transcription factor (HSF) (r = 0.7857, P < 0.01), HSP70 (r = 0.4543, P < 0.01) and HSP27 (r = 0.8782, P < 0.01). A comparison of 15 cows with higher HIF-1α (>482 ng/L) and 15 cows with lower HIF-1α levels (<439 ng/L) showed that reactive oxidative species were higher (P = 0.02), but superoxide dismutase (P < 0.01), total antioxidation capacity (P = 0.02) and glutathione peroxidase (P < 0.01) were lower in higher HIF-1α cows. These results suggested that HIF-1α may be indicative of the risk of oxidative stress in heat-stressed cows and may participate in the response of cows to HS by synergistically activating the expression of the HSP family with HSF.