| Four experiments were conducted to investigate the influence of four diets(acidified waste milk(AWM),pasteurised waste milk(PWM)untreated bulk milk(UBM)and untreated waste milk(UWM))on growth performence,gastrointestine growth and development,and gastrointestine microbiomes of pre-weaned dairy calves,to explore possible mechanism on the influence of dairy by-product waste milk on the microbiomes of different gastrointestinal tract components in pre-weaned dairy calves.Experiment 1,The effects of acidification and pasteurization treatments on the nutrition and microbiological indexes of waste milk were analyzed.The results showed that both acidification and pasteurization could cause the milk fat percentage of waste milk to be reduced to a certain extent,and the acidification of formic acid could cause the milk protein percentage to be improved,and the acidification of formic acid could greatly improve the acidity of waste milk and significantly reduce the pH value(P<0.01),but neither treatment will affect the non-fat milk solids of the waste milk.Formic acidification and pasteurization do not affect the most important dominant genera of waste milk,such as Acinetobacter and Pseudomonas,but pasteurization will affect the waste milk microbial genera and diversity.The total number of pasteurized waste milk microbial genera was 94,which was 105 less than that of the untreated waste milk group,which was 257 less than that of the untreated normal milk group.Experiment 2,Eighty-four newborn Holstein bulls were randomly divided into four groups,fed with acidified waste milk,pasteurized waste milk,untreated bulk milk and untreated waste milk until 42 days of age.Analyze the effects of four diets on calves daily feed intake,daily gain and health condition.The results showed that different diets had no effect on the average daily liquid feed intake of calves in the first two weeks,but could affect it of calves in the third week,and significantly affected it of calves in 4 to 6 weeks(P<0.01),like the average daily liquid feed intake of calves in the pasteurized waste milk group was 0.44 L/d higher than that of the acidified waste milk group.The diets had no effect on the average daily starter intake of calves in 5 to 14 days,but significantly affected it of calves in 3 to 6 weeks(P<0.05),like the average daily stater intake of calves in the acidified waste milk group was significantly higher than that of untreated waste milk group(28.78g/d).The effect of different diets on calves' faecel score was significantly different(P<0.05),and the faecal score of the acidified waste milk group was significantly lower than that of the untreated waste milk group(P<0.05).The diets had significant effect on the daily gain of calves in the first 21 days(P<0.01),but the effect of daily gain in 21-42 days was not significant(P = 0.393).In general,different diets had a significant effect on the average daily feed intake and growth performance of calves in the first 21 days,while that were less affected in the 21-42 days.Experiment 3,Eighty-four newborn Holstein bulls were randomly divided into four groups,fed with acidified waste milk,pasteurized waste milk,untreated bulk milk and untreated waste milk,and randomly selected 6 calves in each group at 21 day and 42 day to carriy out slaughter experiment,respectively.The effects of four diets on calf organ index,dressing rate,pH value of gastrointestinal tracts,intestinal histomorphology,intestinal immunohistochemistry and cellular immune factors were analyzed.The results showed that there were no significant differences in organ index,slaughter rate and gastrointestinal pH value between among 4 groups at both 21 day and 42 day old calves(P>0.05).The pathological changes of immune organs(thymus and spleen)were not observed.The jejunum and ileal inflammation score of calves in the untreated bulk milk group were lower than those in the other groups,but there was no significantly difference in the colon of calves.TLR-4 immunohistochemical staining showed brown granules or agglomerates in the epithelium of jejunum,ileum and colon.The amount of that in formic acid acidified waste milk group and pasteurized waste milk group calves were more,untreated waste milk group existed in small amount,untreated bulk milk group was visible.Furthermore,intestinal mucosa and mesenteric lymph node mRNA detection of calves in formic acid acidified waste milk,pasteurized waste milk and untreated waste milk were all found to have a certain degree of inflammatory response,and formic acid acidification waste milk group calves were obvious.Experiment 4,A total of 84 calves(Holstein;males;single birth)from multifarious cows were used in the study.The calves were randomly assigned to one of AWM,PWM,UBM,and UWM group directly after birth.On postnatal day 21,6 calves from each group were randomly euthanised,and mucosal tissue and digesta samples were collected from the rumen,caecum,colon,and faeces for detection analysis.Our study revealed that a total of 6,5,2 and 10 bacterial genera showed biologically significant differences in the GITs of pre-weaned calves fed four waste-milk diets:acidified waste milk,pasteurised waste milk,untreated bulk milk,and untreated waste milk,respectively.Specifically,generic biomarkers were observed in the rumen(e.g.,Bifidobacterium,Parabacteroides,Fibrobacter,Clostridium,etc.),caecum(e.g.,Faecalibacterium,Oxalobacter,Odoribacter,etc.)and colon(e.g.,Megamonas,Comamonas,Stenotrophomonas,etc.)but not in the faeces.In addition,the predicted metabolic pathways showed that the expression of genes related to metabolic diseases was increased in the calves fed untreated waste milk,which indicated that untreated waste milk is not a suitable liquid diet for pre-weaned calves. |
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