| High temperatures have significant impacts on the health of dairy cows,leading to reductions in their production,reproductive and immune performance.This causes enormous economic losses to China’s dairy industry.To mitigate these issues,Yeast culture,a green additive,has broad prospects for application in livestock and poultry breeding.This is because it can regulate the gut microbiota,improve production and immune performance and enhance antioxidant capacity.Therefore,it is of great importance for dairy farming enterprises to explore the effects of Yeast culture on heat-stressed dairy cows.Doing so can alleviate the economic losses caused by reduced milk production and diseases due to high temperatures in summer.Furthermore,it can provide data references for the development and utilization of feed additives to mitigate heat stress in dairy cows.A randomized complete block design was adopted in this experiment,which consisted of three groups with 15 cows in each group.The control group(CON)was fed with basic feed,while the experimental groups were fed with basic feed supplemented with 100 g/d Yeast culture(SC-1)or 30 g/d of concentrated Yeast culture(SC-2).The cultures were fed to the experimental groups during morning feeding.The experiment lasted for 60 days,including a pre-trial period of 10 days and a formal trial period of 50 days.Temperature and humidity data,milk production,respiratory rate,and rectal temperature were collected during the experiment.On the last day of the trial,the blood was collected and centrifuged to obtain serum,which was immediately stored in liquid nitrogen.Rumen fluid was collected by the rumen pipe method,filtered and stored in liquid nitrogen.Milk samples were collected and sent for testing immediately.Subsequent tests included measurements of temperature-humidity index(THI),respiratory rate and rectal temperature,milk production performance,biochemical indicators,immune indicators,hormone indicators,antioxidant performance,rumen fluid 16 S r DNA,metagenomics and metabolomics.The results showed that during the formal experimental period,the THI of almost all time periods was greater than 72,indicating that the cows were in a state of heat stress throughout the study.Cows fed with the cultures of SC-1 and SC-2 had significantly lower rectal temperature(RT)and respiratory rate(RR)than those in the CON group(P < 0.05).The milk production of the SC-1 and SC-2 groups was significantly higher than that of the CON group(P < 0.05),while the somatic cell count(SCC)was significantly lower in the SC-1 and SC-2groups compared to the CON group(P < 0.05).The UREA content in the SC-1 and SC-2 groups was significantly higher than that in the CON group(P < 0.05).The total antioxidant capacity(T-AOC),glutathione peroxidase(GSH-Px)and superoxide dismutase(SOD)levels in the SC-1 and SC-2 groups were significantly higher than those in the CON group(P < 0.05),while the malondialdehyde(MDA)content was significantly lower(P < 0.05).Compared with the CON group,the serum levels of immunoglobulin A(Ig A),immunoglobulin G(Ig G),immunoglobulin M(Ig M),interleukin-1β(IL-1β),interleukin-6(IL-6),interleukin-2(IL-2),interleukin-4(IL-4),interleukin-10(IL-10),tumor necrosis factor-α(TNF-α),interferon-γ(IFN-γ),and heat shock protein 70(HSP70)in the SC-1 and SC-2 groups were significantly different(P < 0.05).The levels of IgA,IgG,IgM,IL-4,IL-10,and HSP70 in the SC-1 and SC-2 groups were significantly higher than those in the CON group,while the levels of IL-1β,IL-6,IL-2,IFN-γ and TNF-α were significantly lower than those in the CON group.The levels of glucocorticoids(GC),insulin(INS),cortisol(COR)and prolactin(PRL)in the SC-1 and SC-2groups were significantly higher than those in the CON group(P < 0.05),while the levels of triiodothyronine(T3)and thyroxine(T4)were significantly lower than those in the CON group(P < 0.05).Compared with the CON group,the abundance of the rumen microbiota in the Ruminococcaceae family was significantly increased(P < 0.05,LDA > 2)in the SC-1 and SC-2 groups.In addition,compared with the CON group,the SC-1 group showed significant increases in the abundance of the Bacteroidales＿RF16＿group,Eubacterium＿brachy＿group,Butyrivibrio＿2,Eubacterium＿hallii＿group,Moryella,FD2005,Marinilabiliaceae,Methylobacterium,Clostridiales＿vadin BB60＿group,Beijerinckiaceae,Selenomonas＿ruminantium＿AC2024.Furthermore,the pathways of fatty acid biosynthesis and fatty acid metabolism were significantly upregulated in the SC-1 and SC-2 groups compared with the CON group(P < 0.05).In the SC-1 group,the pathways of protein export,PPAR signaling pathway,peroxisome,and adipocytokine signaling pathway were significantly upregulated compared with the CON group(P < 0.05).In the SC-2 group,the pathways mainly involved in carbohydrate metabolism,polysaccharide synthesis and metabolism and cofactor and vitamin metabolism were significantly upregulated compared with the CON group(P <0.05).Metabolomic results showed that compared with the CON group,the concentrations of salicylic acid and 3-methyl-4-(2-(2-methylphenyl)hydrazono)-4,5-dihydro-1H-pyrazol-5-one increased in the rumen of the SC-1 and SC-2 groups,while the concentrations of FAHFA(16:0/18:2)and PC(17:2/22:5)decreased(P < 0.05,VIP > 1).These findings are related to the nutritional aspects of dairy cows.In summary,feeding a culture of Yeast culture can increase milk production,reduce somatic cell count in milk,lower respiratory rate and rectal temperature of cows,enhance their immunity and antioxidant capacity.By using 16 S r DNA and metagenomic sequencing technology,it was found that feeding the cultures increased the abundance of the Clostridia order in the rumen,which had a favorable effect on the breakdown of cellulose and the production of volatile fatty acids(VFAs).Metagenomics provided insights into the rumen microbial functions and showed that feeding Yeast culture upregulated the fatty acid metabolism and biosynthesis pathways in the rumen,while in the SC-1 group,the peroxisome proliferator-activated receptor(PPAR)signaling pathway and the peroxisome pathway were upregulated,which may promote fatty acid breakdown.In the SC-2 group,pathways related to carbohydrate metabolism and polysaccharide synthesis and metabolism were significantly upregulated,which may be related to the generation of VFAs.In pathways related to cofactor and vitamin metabolism,most of the pathways related to vitamin B were significantly upregulated in the SC-2 group,which may be related to the addition of the cultures.In metabolomics,feeding the cultures increased the concentration of salicylic acid in the rumen,which may be related to the anti-inflammatory effect of a certain microbial population. |
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