| This study was to determine differences in the global metabolic profiles and metabolic adaptations to heat stress of different breeds of beef cattle,and the study contained three experiments:(1)The effects of heat stress on performance,nutrients apparent digestibility,endocrine hormone and antioxidant index of different beef cattle breeds.(2)The differences in the global metabolic profiles of different beef cattle breeds.(3)The differences in the global metabolic profiles of different beef cattle breeds under heat stress.Experiment 1: The effects of heat stress on performance,nutrients apparent digestibility,blood indices of different beef cattle breeds: 24 twenty-six-month-old steers were used,including eight Xuanhan yellow cattle,eight Simmental crossbred cattle(Simmental × Xuanhan yellow cattle)and eight cattle-yaks(Jersey × Maiwa yak),and under the same diet for 6 months feeding experiment,by measuring the beef cattle house temperature and humidity index,physiological index,performance,nutrients apparent digestibility,hormone levels and antioxidant index to investigate the effect of heat stress on beef cattle and to evaluate the degree of heat stress of beef cattle in different months.The main results are as follows:(1)April,May and September were non-thermal stress periods,and June to August were thermal stress periods.The respiratory frequency and rectal temperature of each beef cattle breed were significantly increased within the period of heat stress(P < 0.05).Furthermore,the respiratory frequency and rectal temperature of cattle-yak were higher compared with Xuanhan yellow cattle and Simmental crossbred cattle.(2)In comparison with non-heat stress period,Heat stress significantly reduced the dry matter intake per body weight and the average daily gain(ADG)of each beef cattle breed(P < 0.05),and the lowest in August.The degree of performance decreased: cattle-yak>Simmental crossbred cattle>Xuanhan yellow cattle.(3)In comparison with non-heat stress period,heat stress significantly decreased the CP,NDF and Ca digestibility of cattle-yak(P < 0.05),the CP and EE digestibility of Simmental crossbred cattle and the CP digestibility of Xuanhan yellow cattle.(4)In comparison with non-heat stress period,heat stress significantly decreased the serum T3 concentration of cattle-yak(P < 0.05),and the serum T4 concentration of each beef cattle breed(P < 0.05),and the degree of performance decreased: cattle-yak>Simmental crossbred cattle>Xuanhan yellow cattle.Heat stress significantly increased the serum COR concentration of each beef cattle breed(P < 0.05),and the degree of performance increased: cattle-yak>Simmental crossbred cattle>Xuanhan yellow cattle.Heat stress significantly increased the serum HSP70 concentration of each beef cattle breed(P < 0.05),and the HSP70 concentration increased and the activation of heat shock protein protection mechanism were earlier in the Xuanhan yellow cattle in comparison with the Simmental crossbred cattle and cattle-yaks.(5)In comparison with non-heat stress period,heat stress significantly increased the serum MDA concentration of Simmental crossbred cattle and cattle-yak(P < 0.05).Heat stress significantly decreased the serum SOD and T-AOC concentration of Simmental crossbred cattle and cattle-yak(P < 0.05).Heat stress significantly decreased the serum GSH-Px concentration of each beef cattle breed(P < 0.05).And heat stress decreased the antioxidant capacity of beef cattle.(6)In August,the MDA concentration was significantly higher in the Simmental crossbred cattle and cattle-yak comparison with the Xuanhan yellow cattle than Yellow Cattle(P < 0.05),and the SOD concentration was significantly higher in the Xuanhan yellow cattle comparison with the cattle-yak(P < 0.05),and the T-AOC concentration was significantly higher in the Xuanhan yellow cattle comparison with the Simmental crossbred cattle and cattle-yak(P < 0.05).These results indicated that the oxidative stress of the Simmental crossbred cattle was more serious,and the antioxidant capacity is stronger in the Xuanhan yellow cattle comparison with the Simmental crossbred cattle and cattle-yak under the heat stress.Experiment 2: The differences in the global metabolic profiles of different beef cattle breeds: Serum and urine samples were obtained in April(spring season),and the THI in the beef cattle house was approximately 64–68 during this month.We utilized the GC-MS-based metabolomics methodology in combination with PCA and PLS-DA multivariate statistical analysis to obtain differential metabolites of the serum and urine,finally metabolic pathways were obtained for these identified differential metabolites from the KEGG database to study different global metabolic profiles of the above three beef cattle breeds.The main results are as follows:(1)The global metabolic profiles of beef cattle breeds were significantly different.Compared these three cattle breeds with each other,there were 8 differential metabolites between Xuanhan yellow cattle and Simmental crossbred cattle,18 differential metabolites between Xuanhan yellow cattle and cattle-yak,24 differential metabolites between Simmental crossbred cattle and cattle-yak.(2)The metabolic pathway analysis showed that amino acid and lipid metabolism was higher in the cattle-yak comparison with the Xuanhan yellow cattle and Simmental crossbred cattle,purine and vitamin E metabolism was higher in the Xuanhan yellow cattle comparison with the Simmental crossbred cattle and cattle-yak,pyrimidine metabolism was higher in the cattle-yak comparison with the Simmental crossbred cattle,and the rank of tricarboxylic acid cycle: Xuanhan yellow cattle>cattle-yak>Simmental crossbred cattle.Experiment 3: The differences in the global metabolic profiles of different beef cattle breeds under heat stress: Serum and urine samples were obtained in August(summer season),and the THI in the beef cattle house was approximately 76–82 during this month,after the THI in the beef cattle house remained above 80 for 1 week.We utilized the GC-MS-based metabolomics methodology in combination with PCA and PLS-DA multivariate statistical analysis to obtain differential metabolites of the serum and urine,finally metabolic pathways were obtained for these identified differential metabolites from the KEGG database to study different global metabolic profiles of the above three beef cattle breeds under heat stress.The main results are as follows:(1)Under heat stress,the global metabolic profiles of beef cattle breeds were significantly different.Compared these three cattle breeds with each other,there were 33 differential metabolites between Xuanhan yellow cattle and Simmental crossbred cattle,42 differential metabolites between Xuanhan yellow cattle and cattle-yak,33 differential metabolites between Simmental crossbred cattle and cattle-yak.(2)The metabolic pathway analysis showed that glycolytic pathway was higher in the Xuanhan yellow cattle comparison with the Simmental crossbred cattle and cattle-yak,the rank of amino acid metabolism: cattle-yak > Simmental crossbred cattle > Xuanhan yellow cattle,the rank of lipid metabolism: Simmental crossbred cattle>cattle-yak>Xuanhan yellow cattle,purine and vitamin E metabolism was higher in the Xuanhan yellow cattle comparison with the Simmental crossbred cattle and cattle-yak,and the rank of tricarboxylic acid cycle: Simmental crossbred cattle > Xuanhan yellow cattle >cattle-yak.(3)The supply energy to heat stress are heterogeneous.Cattle-yaks mobilize a greater amount of body protein to release glucogenic amino acids to supply energy.Simmental crossbred cattle mobilize a greater amount of body fat to use free fatty acids as an energy source.While Xuanhan yellow cattle have higher glycolytic activity.In conclusion,the metabolic adaptations to heat stress are heterogeneous.Under heat stress,cattle-yaks mobilize a greater amount of body protein to release glucogenic amino acids to supply energy,whereas the TCA cycle is inhibited.In contrast,Simmental crossbred cattle mobilize a greater amount of body fat in order to use free fatty acids and glycerol as energy sources.In comparison with Simmental crossbred cattle and cattle-yaks,Xuanhan yellow cattle change their nutritional energy source without significantly compromising the storage of body fat and protein and the glycolysis process is enhanced.Furthermore,Xuanhan yellow cattle suffer from less oxidative stress and possess a stronger antioxidant defense system and are thus more adapted to hot and humid environments,and heat stress tolerance of cattle-yaks is the lowest. |
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