| The study aimed to investigate the persistent effects of heat stress on production performance and oxidative balance of dairy cows.Gas chromatography-mass spectrometry(GC-MS)was used to explore endogenous differential metabolites in serum and milk of dairy cows under heat stress by means of metabonomics,and to find diagnostic markers of heat stress cows,so as to provide a theoretical basis for cow’s body recovery and its physiological mechanism after heat stress.The experiment consisted of heat stress group and non-heat stress group according to THI index,and the 2 experiment was conducted in August 2017 and March 2018,respectively.We recorded the dairy cow’s house temperature 3 times per day(6:00A.M,12:00A.M,18:00P.M),and obtained the daily average THI value.Under the conditions of continuous hot or continuous suitable weather,20 dairy cows were selected(BCS=3.00±0.25,LC=2.5±0.5,Age=3.5±0.5,DIM=115±5).Milk and serum samples were collected at 13:00 P.M(before milking),and each group was continuously tracked for 2 months,and samples were taken every 30 days for a total of 3 times.The milk yield and milk index were statistically analyzed,serum antioxidant index was measured by ELISA,and metabolomics analysis was performed on blood and milk.The results of milk yield showed that heat stress significantly reduced milk yield of dairy cows at all stages(P < 0.05).With the decrease of THI,milk yield did not improve significantly(P > 0.05)from moderate heat stress(80 < THI < 90)to heat stress threshold(THI = 72)to complete regression of heat stress(THI < 72)During the whole test period(62d),the total milk yield of dairy cows in the heat stress group was 351 kg lower than that of the non-heat stress group.Milk index result: Compared with the non-heat stress group,the milk fat rate,milk protein rate,non-fat solid rate and total lactose of the milk samples in the heat stress group were significantly decreased(P<0.05),and the lactose rate had no significant change(P>0.05).With THI continues to decrease,none of the above indicators changed significantly(P>0.05).Serum antioxidant index result: The concentrations of serum SOD and GSH-Px in the heat stress group were significantly lower than those in the non-heat stressgroup(P<0.05),while the MDA concentration increased(P<0.05).During the experimental period,as THI continued decrease,the above indicators did not improve significantly(P<0.05).Serum metabolites result: Heat stress changed many metabolic pathways in the blood of dairy cows,including glycolysis(glycemic,lactose),gluconeogenesis(propionic acid),lipid metabolism(stearic acid,3-hydroxybutyric acid),amino acid metabolism(serine,alanine),Acid,glycine,threonine,valine,leucine,leucine,urea nitrogen)and microbial metabolism(imine).Milk metabolites result: Heat stress changed many metabolic pathways in the mlik of dairy cows,including Glycolysis(lactic acid),amino acid metabolism(milk urea nitrogen,alanine,valine,glycine,lipid metabolism(acetic acid,sunflower acid,myristic acid,palmitic acid,stearic acid),and succinic acid cycle... |
