| The environmental temperature(T)and humidity are closely related to the health of dairy cows.The impact of cold and heat stress on production of dairy cows is a bottleneck problem which needs to be solved urgently.The purpose of this study is to investigate the effects of ambient temperature and humidity changes on dairy performance,physiological and biochemical indicators,immune function and fecal microbial diversity,and to screen out indicators for evaluating cold and heat stress in dairy cows and to determine suitable temperature and humidity range of comfortable environment for dairy cows production in south China,thereby providing scientific parameters for predicting cold and heat stress in dairy cows and support for precise control of dairy cows under intensive conditions.The experiment selected 32 lactating Holstein cows with similar body weight(627 ± 58 kg),lactation days(120-180 days),parity(1-3)and somatic cell counts(<500,000 / mL)and rdivided into four groups : spring group,summer group,autumn group and winter group.Every trial lasted 40 days.Dairy cows accessed to food and water freely.The results were as follows:(1)The average temperature and humidity index(THI)of spring,summer,autumn and winter in Wuhan was 61.74 ± 3.59,85.09 ± 1.29,61.95 ± 2.95 and 42.97 ± 5.19,respectively.The rectal temperature(RT)and respiratory rate(RR)of the cows in summer were the highest among the four seasons when the THI was 85.09,and the corresponding daily average RR and RT were up to 103.71 ± 1.93 times/min and 39.91 ± 0.23 °C,respectively.The RR and RT in winter were the lowest when the THI was 42.97,and the corresponding daily average RR and RT were 21.70 ± 1.70 times/min and 38.26 ± 0.39 °C,respectively.(2)When the THI was 85.09 in summer,the daily milk yield and 4% standard milk of dairy cows were significantly lower than that in spring(P<0.05).The milk fat percentage was the lowest in summer and significantly lower than that in winter(P<0.05),and the milk protein rate was the lowest in autumn and significantly lower than spring and summer(P<0.05).Urea nitrogen content in spring was significantly lower than the other three seasons(P<0.01).The digestibility of DMI,DM and CP were the lowest in summer and significantly lower than the other three seasons(P<0.01).The digestibility of EE and NDF in summer were both significantly lower than that in spring and winter(P<0.01)and autumn(P<0.05).The standing time of dairy cows in spring was significantly lower thanthat in the other three seasons(P<0.01),meanwhile,there was significant difference between summer and winter(P<0.05).The feeding time of cows in summer was significantly lower than that of cows in autumn and winter(P<0.05).The frequency of chewing in summer was significantly lower than that of the other three seasons(P<0.01),and it was significantly lower in autumn than that in spring and winter(P<0.05).The frequency of drinking in summer was significantly higher than that of the other seasons(P<0.01),and it was significantly higher in autumn than that in winter(P<0.05).(3)SOD in serum among the four seasons had significant difference(P<0.01).CAT in serum was significantly higher in winter than the other three seasons(P<0.01),and the difference between spring and autumn was significant(P<0.05).The levels of prolactin and luteinizing hormone in spring cows were significantly higher than those in the other three seasons(P<0.01)and the level of luteinizing hormone was significantly higher in winter than that in summer and autumn(P<0.01).The content of progesterone in autumn was significantly higher than that in summer and winter(P<0.05).The content of cortisol in dairy cows was significantly different among the four seasons(P<0.01).Adrenalin content in autumn and winter had significant difference(P<0.05).The HSP70 content was significantly higher in summer than that in the other three seasons(P<0.01),and it was significantly lower in winter than the other three seasons(P<0.01)and there was also a significant difference between spring and autumn(P<0.05).In addition,the levels of pro-inflammatory cytokines IL-1β and TNF-α in serum in summer were significantly higher than those in the other three seasons(P<0.01),while the IgG content in summer was significantly lower than the other three seasons(P<0.01),and it was significantly higher in spring than that in winter(P<0.01),and there was also a significant difference between autumn and winter(P<0.05).(4)There were 765 OTUs in the cows fecal samples of the four seasons,accounting for 76% of the total OTUs.The unique OTUs of cows in spring,summer,autumn and winter were 6,11,1 and 4,respectively.The dominant bacteria in the four experimental groups were selected as the Firmicutes and Bacteroidetes,and the sum of their abundances accounted for 92% of the total bacteria.Meanwhile,more than 5% of the dominant bacteria were Romboutsia,Paeniclostridium,Ruminococcaceae UCG-005/014,Clostridium sensu stricto 1,Turicibacter,Christensenellaceae_R-7_group,Rikenellaceae RC9 gut group,Eubacterium_coprostanoligenes_group),Lacnospiraceae_NK3A20_group,Provobacterium(Prevotellaceae UCG-003),Bifidobacteium,and Solibacillus.The content of Bacteroides in the summer was significantly decreased(P<0.01),however,the content of Proteobacteria was significantly increased(P<0.05).(5)THI and T were significantly correlated with RT,RR,daily milk yield,Cor and T4,respectively(P<0.01).The THI inflection point of the milk yield change was 68.31,and the T inflection point was 17.22 °C.When the environment T was 10 °C~20 °C and the THI ranged 55~65,the RR and RT of the cow ranged 25.30 times/min~44.02times/min and 38.14 °C~38.96 °C.When the THI exceeded 68.31,the milk yield began to decrease.Through the quadratic curve relationship,it was found that when the milk yield was the highest,the THI was 56.98 and the milk yield decreased by 5.20%,so the optimal THI of the cow was 45.65~68.31.When T exceeded 17.22 °C,the milk yield began to decrease.Through the quadratic curve relationship,it was found that when T was14.43 °C,the milk yield is reduced by 1% and the optimum T of the cow is11.64 °C~17.22 °C.(6)The bivariate and partial correlation coefficients of THI or T and RT or RR were all above 0.8.THI and milk fat percentage were significantly correlated in bivariate correlation and partial correlation analysis(P<0.05),and significant difference(P<0.05)in bivariate correlation analysis with urea nitrogen and lipoprotein ratio,while the difference was extremely significant in the partial correlation analysis(P<0.01).T was significantly correlated with milk fat percentage,urea nitrogen and fat-protein ratio in both bivariate and partial correlation analysis(P<0.05).In addition,THI was significantly associated with IgG(P<0.01)in the bivariate analysis,and the difference between THI and SOD was significantly different(P<0.05),while the difference was extremely significant(P<0.01)in partial correlation analysis.THI was consistent with TNF-α,GPX,T-AOC,CAT,MDA and ALP in bivariate correlation and partial correlation analysis(P<0.05).In the bivariate analysis,T was significantly(P<0.01)or significantly associated with TNF-α and IgG(P<0.05).T was significantly different from GPX,SOD,T-AOC and MDA in the partial correlation analysis(P<0.05)or extremely significant correlation(P<0.01).T was significantly correlated with CAT and ALP in both bivariate and partial correlation analyses(P<0.01).In summary,high THI 85.09 or low THI 42.97 reduced milk production and RT,decreased lactation-related hormone and IgG levels,elevated stress hormone levels.Both RR and RT were significantly increased at high THI 85.09.The increase of RT caused the decrease of beneficial microorganisms(Bacteroides and Prevotellaceae UCG-003)indairy cow feces,and increased harmful microorganisms(Proteobacteria).THI,T,RR,RT,Cor,HSP70 and ruminating time were selected to evaluate the cold and heat stress of dairy cows.Meanwhile,the suitable environment T of the cows was 10 °C~18 °C(when the humidity was 70 %~80 %),and the suitable THI was 45~68 in south China. |
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