Effects Of Different Protein Source Combinations In Milk Replacer On Growth Performance And Intestinal Development Of Suckling Calves

The main objective of this study was to research the combined effect of vegetable protein sources in milk replacer for suckling calf,and to optimize the combination of protein sources of milk replacer based on the content ratio of protein source components.To investigate the effects of different protein source combinations on growth performance,digestion and metabolism,serum biochemical and immune indicators,intestinal organs and tissue morphological development of suckling calves.In this experiment,sixty-four newborn Holstein calves were randomly assigned to one of four groups,which were fed with milk replacer whose proteins contained 30% milk protein(MP)and 70% vegetable protein of crude protein.Vegetable proteins were soybean protein isolate(SP),wheat hydrolyzed protein(WP)and rice protein isolate(RP),respectively.Calves in different groups were fed one of the four milk replacers as follows: A)30%MP+70%SP;B)30%MP+40%SP+10%WP+20%RP;C)30%MP+10%SP+40%WP+20%RP;D)30%MP+10%SP+20%WP+40%RP.The trial lasted for 63 days.Part 1: Effects of different protein source combinations in milk replacer on growth performance,energy and nitrogen metabolism of sucking calvesIn this trial,individual feed intake of calves was recorded daily body weight and body size were measured at 14,42 and 63 day-old.Six calves per group were moved into metabolism cages individually.The results showed as follows: 1)Body weight and average daily gain of calves in B group were significantly higher than that in A group(P<0.05).However,there were no significant differences on starter intake,dry matter intake and the ratio of feed to gain among all groups(P>0.05).2)At 14 to 63 day-old,withers height and hip height of calves in B group were significantly higher than that in A group(P<0.05).3)The difference in nitrogen retained and RN/DN among the groups were not significantly(P>0.05).At 56 day-old,the difference of energy and nitrogen metabolism among groups were also not significant(P>0.05).4)Throughout the whole period of the experiment,the serum growth hormone(GH)and insulin-like growth factor(IGF-1)levels of calves in group A were significantly lower than other groups(P<0.05).Part 2: Effects of different protein sources combinations in milk replacer on blood metabolites and intestinal development of suckling calvesBlood samples were drawn on 28 and 56 day-old to measure serum concentration of metabolites.On 63 day-old,six calves in each group were slaughtered and villus size of small intestine(duodenum;jejunum and ileum)mucosa was determined.The results showed as follows: the capatity of anti-oxidant were significantly higher in B and D groups than in control group during the experimental period(P<0.05).No difference were observed in IgG,IgA and IgM concentrations among all the treatments at the experiment period(P>0.05).The concentrations of serum DAO were higher in D and A groups than in other groups at 28 day-old(P<0.001),and were greater in C and D groups at 56 day-old(P<0.001).The LPS concentrations has the similar trend with DAO at 56 day-old(P<0.001).D group showed a significantly decreased villus height in duodenum and jejunum compared to C group in the duodenum and jejunum(P<0.05).Villus height of ileum in B group had a tendency for increased compared to D group(P=0.076),and the villus height to crypt width ratio of B group was significantly higher than in A and D groups(P<0.05).Part 3: Effects of different protein sources combinations in milk replacer on short-chain fatty acid profile,intestinal development and intestinal bacterial community of suckling calvesAt the end of the trial,six calves with similar body weight from each group(63 day-old)were slaughtered.Within 20 min after slaughter,the gastrointestinal tract was removed.Samples of duodenum,jejunum and ileum were collected for short volatile fatty acids(SCFAs)and intestine bacteria measuring.The results showed that the contents of acetate,propionate and butyrate of group B was significantly higher than that of group D(P<0.05).The community richness of ileal microorganisms in group B was significantly higher than that in other treatment groups(P<0.05).There were no significant differences in the diversity of calf ileal microorganism communities(P>0.05).The differences of microorganism at genus were Olsenella,Intestinibacter,Lachnospiraceae_NK3A20,Syntrophococcus,g_unclassified_f_Lachnospiraceae,Howardella(P<0.05).Based on the correlation analysis between the top 50(genus level)bacteria with relative abundance in the ileum and the SCFAs in the ileum,it was found strong correlation between the differences of microboita at genus and SCFAs(P<0.05,r> 0.50).In conclusion,the feeding of compound vegetable protein milk replacers can improve the growth performance,antioxidant capacity and immune capacity of suckling calves.30%MP+40%SP+10%WP+20%RP compound vegetable proteinmilk replacer was the bestin our experiment;in addition,the combination of different protein source milk replacers can affect the composition of intestinal flora and the content of intestinal SCFA,thereby affecting the development of intestine.Group D(30%MP+10%SP+20%WP+40%RP)rich in gluten has an inhibitory effect on the intestinal development of calves.Provide a basis for the development of double protein in milk replacers.