| The purpose of this study was to investigate the effects of starter feed supplementation on growth performance and immune organ development of yak calves.20 healthy 1-month-old Datong yak calves(male)with similar birth age and weight were selected and randomly assigned to 2 treatments(n=10).Calves in the C group were fed milk replacer and alfalfa hay,the calves in S group were fed with starter feed based on the C group,the calves in two groups offered the same of dry matter intake daily.When the dry matter intake of yak calves reached about 1 kg/d,5calves from each group were slaughtered.Liver,thymus and spleen were sampled for measurement of the organ morphology and the contents of hormones and cytokines,and further study enrichment of metabolites and pathways of metabolism of different metabolites based on LC-MS metabolome of liver.Differentially expressed genes in liver,thymus and spleen of yak calves were analyzed by RNA-Seq.Finally,the functions of different expression of genes were annotated by GO(Gene Ontology),and the pathways of enrichment were analyzed by KEGG(Kyoto Encyclopedia Genes and Genomes)to study the effects of starter feed supplementation on the immune organ function of yak calves.The main results are as follows:(1)From 60 to 180 days old,yak calves were supplemented with an average of331.35 g of starter feed every day.Compared with the C group,the average daily feed intake of the S group increased by 8.88%,the average daily weight gain of the S group increased by 0.48 kg,and the thymus organ index of the supplemented group increased by 57% compared with the C group,and the content of Ig G,Ig M,Ig A,IL-2,IL-4,IL-6,M-CSF,IFN-β,IFN-γ and TNF-α immune factors in yak calves serum in S group was significantly higher than that in C group(P<0.05).Starter feed supplementation significantly improved the growth performance of yak calves and the content of immune factors in blood,thus positively regulated the immunity of yak calves.(2)Starter feed supplementation promote the development of yak calves hepatocytes.When compared with the C group,the liver of yak calves in S group exhibited a significantly increased the cytokines content of liver(P<0.05).A total of149 differential metabolites were screened from the liver of yak calves in two groups,among which 56 were up-regulated and 93 were down-regulated.Analysis showed that the differential metabolites are mainly lipid and lipid molecules,organic acids and their derivatives,nucleosides,nucleotides and analogues.There were 1003 differential genes in liver of yak calves in two groups,of which 568 were up-regulated genes and 435 were down-regulated.Differentially expressed genes are mainly involved in oxidative phosphorylation,glycine,serine and threonine metabolism,starch and sucrose metabolism and other pathways.Starter feed supplementation can enhance the metabolism of carbohydrates,fats and amino acids in the liver,and enhance the antioxidant function and immune function of the liver mainly by enhancing amino acid metabolism,thus positively regulating the liver development and immune function of yak calves.(3)The thickness of thymus cortex and the content of thymosin in S group were significantly higher than those in C group(P<0.05),but there was no significant difference in the content of thymic cytokines(P>0.05).Transcriptional analysis showed that there were 2004 differentially expressed genes in thymus of yak calves in two groups,of which 793 were up-regulated genes and 1211 were down-regulated.Starter feed supplementation can enhance the immune function of yak calves of thymus by down-regulating PI3K-Akt signal pathway dependent on genes such as TLR2,TLR4,ECM and PI3 K and up-regulating NF-κB signal pathway dependent on genes such as TNF-α,LBP,TCR,ELC and ICAM.(4)The radius of spleen nodule in S group was significantly larger than that in C group(P < 0.05),and the content of cytokines in spleen was significantly higher than that in C group(P < 0.05).There were 772 differentially expressed genes in the spleen of yak calves in two groups,among which 389 were up-regulated genes and 383 were down-regulated.Starter feed supplementation can enhance the immune function of spleen mainly by up-regulating the complement and coagulation cascade dependent on genes such as FI,C1 qrs,C1INH(SERPING1),C3AR1,VWF,MCP,F13 and FGB,and by up-regulating antigen processing and presentation dependent on genes such as HSP70、CD8A、CD8B、102272312、102278697 and 102273821.It is concluded that starter feed supplementation can increase the nutritional intake level of yak calves,improve their growth performance and the content of immune factors in blood.Starter feed supplementation can enhance the amino acid metabolism of yak calves of liver,thus promoting the sound development of its liver morphology and function,glycine,serine and threonine metabolism may be the key amino acid signaling pathway to establish nutrition and immunity.Starter feed supplementation can promote the development of yak calves of thymus and the secretion of cytokines,mainly by down-regulating PI3K-Akt signal pathway and up-regulating NF-κB signal pathway to enhance the immune function of thymus.At the same time,starter feed supplementation also promoted the development of yak calves of spleen and the secretion of cytokines,mainly through up-regulating complement and coagulation cascade,antigen processing and presentation and other pathways to enhance the immune function of spleen.It is suggested that supplementation proper amount of starter feed yak calves in lactation can not only improve their growth performance,but also promote the morphological and functional development of their immune organs,thus being more conducive to the early healthy growth of yak calves. |
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