| Feeding milk replacer can effectively promote the growth and development of calves.However,milk replacer is often made with a high percentage of vegetable protein,which is difficult for calves to fully digest and utilize because the calf’s digestive system is not fully developed at this stage.It is easy to cause diarrhea and even death of calves.By adding acidifier to the milk replacer to make acidified milk,it can effectively inhibit the growth of pathogenic bacteria and better maintain the quality of the milk replacer.Feeding acidified milk reduced the diarrhea rate of calves and improved the health of calves.Therefore,this study was conducted to analyze the changes in milk composition,microbiota composition and metabolites of acidified milk through the acidification test of milk replacer.On the other hand,calf feeding trials were conducted to analyze the differences in calf growth performance,serum biochemistry,fecal microbiota and serum metabolites,to investigate the effects of feeding acidified milk on early calf growth performance,fecal microbiota and organism metabolism.To investigate the effects of feeding acidified milk on the growth performance,fecal microflora and body metabolism of early calves,and to elucidate the mechanism by which acidified milk affects calf performance.Experiment Ⅰ.Effect of acidification treatment on the nutrient composition,milk microorganisms and metabolites of milk replacer.The control group was prepared by dissolving milk replacer using warm water and stirring well in the ratio of 1:7.In the acidified milk group,the same preparation method was used,followed by the addition of acidifier to adjust the milk p H to 4.0-4.5.The milk in both groups was stored at room temperature and transferred to-80 ℃ refrigerator at 12,24 and48 h after preparation,followed by milk composition,16 S r RNA gene sequencing and milk metabolomics profiling.The results showed that:(1)At 12 h,the lactose percentage and milk fat percentage of acidified milk were significantly lower than those of control group(P < 0.05),and the milk protein percentage was significantly higher than that of control group(P < 0.05).At 24 h,the milk fat percentage and non-fat solid percentage of acidified milk were significantly lower than those of control group(P < 0.05).At 48 h,the lactose percentage,milk fat percentage and non-fat solid percentage of acidified milk were significantly lower than those of control group(P < 0.05).With the increase of time,milk lactose percentage,milk fat percentage and non-fat solid body percentage in two groups were significantly decreased(P < 0.05),while milk protein percentage was increased with the increase of time content(P < 0.05).The p H value of milk in both groups was significantly decreased with the increase of time(P < 0.05).At the same time point,p H of acidified milk was significantly lower than that of control group(P < 0.05).(2)The Chao 1,ACE,Shannon and Simpson indices of α-diversity were significantly higher in acidified milk than in the control group at the same time(P < 0.05).The principal component results showed that the bacterial community structure was significantly different between acidified milk and control milk at each time point(P < 0.05).The abundance of beneficial bacterial genera such as Streptococcus,Lactococcus,Lactobacillus and Anoxybacillus in acidified milk was higher than the control group at all time points(P <0.05).In addition,Bacillus,Pantoea and Enterococcus were less abundant than the control(P < 0.05).(3)The results of principal component analysis of metabolites showed that significant separation of metabolites occurred between acidified milk and control group at each time point.The two groups of milk screened 36,41 and 45 differential metabolites at 12,24 and48 h.The acidified milk group increased the content of lipid compounds related to linoleic acid metabolism and long-chain fatty acids,and increased the content of metabolites of functional substances of antibacterial and antioxidant functions such as lacto-photochrome,phenylacetic acid,propionyl carnitine and sweet pepper alcohol compared to the control group.Experiment Ⅱ.Effect of early feeding of acidified milk to calves on their growth performance,faecal microbiology and serum metabolism.Sixteen healthy newborn calves with similar birth date(20 ± 2 d)and weight were randomly divided into 2 groups,each group was fed with milk replacer(control group)and acidified milk replacer(acidified milk group).The pre-testing period was 7 days and the main test period was 60 days.Weighing and ear vein blood collection were performed before morning feeding on days 30 and 60.Fecal collection was performed on day 7 of the formal trial,and thereafter at one-week intervals for a total of seven times.The results show that:(1)There was no significant difference in mean daily weight gain,liquid and solid feed intake of calves in the acidified milk group at 30 and 60 days compared to the control group,but there was a trend of higher solid feed intake of calves in the acidified milk group from31-60 days compared to the control group(P=0.05),and fecal score and diarrhea rate of calves from 1-30 and 30-60 days were significantly lower than those of the control group(P< 0.05).(2)There was a trend for higher serum glucose levels in calves in the acidified milk group than in the control group at days 30 and 60(P = 0.060,P = 0.097),while other serum biochemical parameters were not significantly different from the control group.Immunoglobulin G was significantly higher in calves of the acidified milk group than in the control group at day 30(P < 0.01),and interleukins 2,4 and 10 were significantly higher on days 30 and 60(P < 0.01).SOD,GSH-Px and total antioxidant capacity were significantly higher(P < 0.01)and MDA content was significantly lower(P < 0.01)in the calves of the acidified milk group on day 30 and 60 than in the control group.(3)The Chao1 index and Shannon index of the fecal microbiota of the cows in the acidified milk group did not differ from those of the control calves.Significant differences(P < 0.05)were found in the structure of fecal flora between the two groups of calves at weeks 1,2,3,5 and 6 at each time point.At the Phylum level,feeding the acidified milk group caused differences in the dominant Phylum between the two groups of calves,with the p Hylum Firmicutes being the dominant fecal p Phylum in the acidified milk group and its abundance being higher than that of the control group(P <0.05).At the genus level,the abundance of Bacillus spp.,Megasphaera and Lactobacillus was lower in the acidified milk calves than in the control group(P <0.05),but the relative abundance of Prevotella 9,all Prevotella and Tyzzerella 4 was lower than in the control group(P <0.05).(4)A total of 61 differential metabolites were screened according to VIP>1.5 and FDR adjusted for P < 0.05.Metabolites were enriched in β-alanine metabolism,vitamin B6 metabolism,valine,leucine and isoleucine degradation,tricarboxylic acid cycle,pyruvate metabolism,cysteine and methionine metabolism,glutathione metabolism and other pathways,and the serum of calves in the acidified milk group showed significantly higher levels of antioxidant functional substances ferulic acid,homoglutathione The levels of ferulic acid,homoglutathione and malonic acid,allosteric acids such as isovaleric acid and2-methylbutyric acid and branched-chain amino acid L-isoleucine were significantly increased in the serum of the acidified milk group compared with the control group.In conclusion,acidification of milk replacer changed the composition of substances,flora structure and metabolites in milk,increased the relative abundance of beneficial bacterial genera and significantly increased the concentration of antioxidant and antibacterial functional substances in milk.Feeding acidified milk calves increased solid plant feed intake in late lactation,optimized the structure of calf digestive tract flora,reduced fecal scores and diarrhea rates in calves,and improved antioxidant and immune capacity in early calves. |
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