Heat stress affects dairy cow health status through blood oxygen availability

Abstract

Background: Rises in global warming and extreme weather occurrence make the risk of heat stress (HS) induced by high ambient temperatures more likely in high-yielding dairy cows, resulting in low milk quality and yield. In animals, oxygen is involved in many physiological and metabolic processes, but the effects of HS on oxygen metabolism remain unclear. Thus, the current study aimed to investigate how oxygen metabolism plays a role in health status of dairy cows by measuring the milk yield, milk composition, and blood biochemical variables of cows under different levels of HS: none (No-HS), mild (Mild-HS), and moderate HS (Mod-HS).

Results: The HS significantly increased rectal temperature (P_treat < 0.01) and respiration rate (P_treat < 0.01). Under Mod-HS, greater Na⁺ (P < 0.05) and lower total CO₂, and pH (P < 0.05) were observed relative to those under No-HS and Mild-HS. Oxygen concentrations in both coccygeal artery and mammary vein (P_treat < 0.01) were lower under Mod-HS than under No-HS. Coccygeal vein concentrations of heat shock protein 90 (HSP90) (P < 0.05) increased during Mod-HS compared with those in cows under No-HS. Malondialdehyde increased during Mod-HS, and glutathione peroxidase (P < 0.01) increased during Mild-HS. Coccygeal vein concentrations of vascular endothelial growth factor (P < 0.01), heme oxygenase-1 (P < 0.01), and hypoxia-inducible factor 1α (P < 0.01) were greater in cows under Mod-HS than those under No-HS. Red blood cell count (P < 0.01) and hemoglobin concentration (P < 0.01) were lower in the coccygeal vein of dairy cows under Mild- and Mod-HS than those of cows under No-HS.

Conclusions: Exposure to HS negatively impacts the health status and lactation performance of dairy cows by limiting oxygen metabolism and transportation. However, the specific mechanism by which HS affects mammary function in cows remains unclear and requires further exploration.

Keywords: Dairy cow; Health status; Heat stress; Lactation performance; Oxygen metabolism.

Fig. 1

Pearson correlation analysis between blood gas profiles and oxidative stress in cow coccygeal veins under no heat stress (A), mild heat stress (B), and moderate heat stress (C). MDA, malondialdehyde; SOD, superoxide dismutase; GSH-Px, glutathione peroxidase; T-AOC, total antioxidant capacity; HO-1, heme oxygenase 1; VEGF, vascular endothelial growth factor; HSF, heat shock transcription factor; HIF-1α, hypoxia inducible factor 1α; HSP90, heat shock protein 90; HCT, hematocrit; HGB, hemoglobin; TCO₂, total pressure of carbon dioxide, pCO₂, partial pressure of carbon dioxide; pO₂, partial pressure of oxygen, sO₂, oxygen saturation; Color gradients indicate the degree of correlation, with blue indicating a positive correlation and red indicating a negative correlation. ^***P < 0.001, ^**P < 0.01, ^*P < 0.05