Effects Of Three Feeding Patterns On The Development Of Digestive Tract And Microbiota Composition In Calves

The remarkable characteristics of calves(from birth to 6 months of age)are that the immune system and digestive system are not fully developed and growth rate is the high.Therefore,better calf breeding can significantly reduce the mortality,and will further affect the milk production performance and longevity of adult cattle.In addition to genetic basis and the external environment,the feeding pattern is an important factor that affects quality of calf breeding,and is also the most important purpose in practice of grazing management.Therefore,this study used male dairy calves as animals(from birth to the 80 days of age)and studied the effects of three different feeding patterns(Group A:milk+concentrate;Group B:milk+concentrate+hay;Group C:milk+TMR)on growth and digestive tract development of calves.The effects of different feeding patterns on the microbital composition and functions in digestive tract(rumen+ileum)were studied by using metagenomic sequencing.The main results are as follows:1.Effects on growth and digestive tract development:Under the three feeding patterns,there was no significant difference in average daily gain between the three groups(P>0.05),but the feed conversion rate(ratio of feed,forage to weight gain)of Group A and Group B were significantly higher than that of Group C(P<0.05),while there was no significant difference between Group A and Group B(P>0.05).At the 80days of age,there was no significant difference in rumen weight among the three groups(P>0.05),but the p H value of rumen contents in group B was significantly higher than that in group A and group C(P<0.01),and that in group C was also significantly higher than that in group A(P<0.01).The mean of rumen papilla number of calves in the three groups were 5.28±1.40/cm~2,6.99±2.15/cm~2 and 8.27±1.57/cm~2,respectively.Group C was significantly higher than Group A(P<0.01),significantly higher than Group B(P<0.05),and Group B was significantly higher than Group A(P<0.01).Through histological examination,there are certain differences in the histological structure of rumen and ileum epithelium between different groups,but it is difficult to find obvious rules.2.Microbital composition in digestive tract:12316 Mb and 12532 Mb Clean Reads were obtained from each sample of rumen and ileum tissues by macro genome sequencing;170769(N50=3420 bp)and 123046(N50=1903 bp)Scaftigs were assembled;The predicted average number of genes was 665644 and 450986,of which86%were annotated on bacteria,while the remaining 14%were not successfully annotated.Compared with group A,the abundance of Bacteroidetes and Spirochaetes in the rumen of calves in group B was higher,while the abundance of Firmicutes was lower;The abundance of Bacteroidetes and Mucoromycota in the rumen of calves in group C was higher,and the abundance of Firmicutes was lower.Compared with group C,the abundance of Mucoromycota and Spirochaetes in the rumen of calves in group C was higher.Compared with group A,the abundance of Tenericutes in the ileum of calves in group B is higher,and the relative abundance of microbial flora in the ileum of calves in group C is not significantly different at the level of the phylum.Compared with group B,the abundance of Tenericutes in the ileum of calves in group C was lower.When the structure of intestinal microflora in different groups is compared at the generic level,the difference between them is smaller.3.Microbiotal functions in digestive tract:Based on the functional annotation of KEGG,egg NOG,CAZy and other databases,the difference analysis between Anosim groups,metabolic pathway comparison analysis,Metastat and LEf Se analysis of functional difference between groups were carried out.The results showed that in most cases,the differences of between-groups were not significant(P>0.05)because of the large differences of within-groups.However,in contrast,the functional difference of rumen microbial flora between groups is more obvious than that in ileum.In conclusion,this study compared the differences in individual growth,digestive system development,gut microbial characteristics of calves under three feeding patterns.On the whole,the feeding pattern of"milk+TMR feed"is preferable according to the results obtained in this study.