This study was designed to investigate the effect of heat stress on body weight, physiological parameters, milk yield, and metabolome of milk and plasma in dairy cows by using Hydrogen-1Nuclear Magnetic Resonance Spectrometry (1HNMR)-based metabolomics approach. Ten Holstein cows in heat stress period (28 d) and another ten Holstein cows in thermo-neutral period (28 d) were maintained at the same feeding and management regime. Cows under both treatments were similar in parity, body weight, and days in milk at the beginning of each period. Bodyweight of each cow was recorded at the beginning and end of each period. Milk production, rectal temperature, and respiration rate were recorded weekly under each treatment while Blood samples and milk samples for 1HNMR analyses were collected at the end of each period. Cows in heat stress period had greater respiration rates (p<0.01), greater rectal temperatures (p< 0.01), lower milk yield (p< 0.01) and lower milk protein percentage (p=0.02) than cows in thermo-neutral period. Cows in heat stress period exhibited the greater milk concentrations of N-acetyl glycoprotein (NAG), choline, scylloinositol, pyridoxamine and lower milk concentrations of O-acetyl glycoprotein (OAG), citrate, glycerophosphocholine (GPC) and methyl phosphate than those in thermo-neutral period. Besides, cows in heat stress period showed greater plasma concentrations of alanine, glutamate, glucose, urea, histidine, 1-methylhistidine (1-MH) and formate. However, the plasma concentration of very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), lipid, leucine, and 3-hydroxybutyrate (3-HB) were lower as compared to cows in the thermo-neutral period. In conclusion, heat stress affects the metabolites in milk and plasma in dairy cows. It is reflected by the alteration of 8 metabolites in milk and 12 metabolites in blood plasma. Which are mainly involved in gluconeogenesis, proteolysis, and milk fatty acid synthesis. Because of their capability to hit multiple targets, these metabolites could be selected as the potential biomarkers for dairy cows undergoing heat shock. The biological significances of the metabolite changes in the milk and plasma were also analyzed.
metabolomics; dairy cow; biomarkers; nuclear magnetic resonance
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