After the birth of a yak calf,the early adaptation of calves to solid feed is critical to their growth and digestive system development,as it involves the transition from liquid to solid feed and from a non-ruminant to a ruminant nutritional type.It is considered the focus of calf breeding.The aim of this experiment was to inves-tigate the effects of different feeding levels of solid feed on the development of pancreas in suckling yak calves using non-targeted metabolomics techniques.Twenty-one healthy yak calves(males)with similar age[(60± 3)days of age]and weight[(44.45±2.50)kg]were selected as test animals and randomly divided into three groups:the low feeding group(40％feed intake group,IR40 group),the medium feeding group(70％feed intake group,IR70 group)and the high feeding group(free feeding group,AL group),with 7 yak calves in each group.All three groups were fed equal amounts of milk replacer and different amounts of solid feed(con-centrate and alfalfa hay).The pretest period lasted for 30 days,and the test period lasted for 90 days.The re-sults showed as follows:1)the body weight,pancreatic organ index and total percentage of external secretory part area were significantly higher in the AL group than the IR70 group(P＜0.05);additionally,the body weight,pancreatic weight,pancreatic organ index and total percentage of external secretory part area were sig-nificantly higher in the AL group than the IR40 group(P＜0.05).2)Pancreatic amylase,pancreatic protease activity and insulin content were significantly higher in the AL group than the IR70 group(P＜0.05).Moreo-ver,pancreatic amylase,trypsin and chymotrypsin activities and glucagon,insulin and growth inhibitor con-tents were significantly higher in the AL group than the IR40 group(P＜0.05);glucagon content was signifi-cantly higher in the IR70 group than the IR40 group(P＜0.05).3)Metabolomic analysis revealed a significant increase in ergocalciferol content in steroid biosynthesis in the IR70 group compared with the AL group(P＜0.05);progesterone content was significantly increased in the oocyte meiotic pathway,progesterone-mediated oocyte maturation pathway and breast cancer pathway(P＜0.05);in the pyrimidine metabolic pathway,the contents of deoxycytidylic acid and uracil were significantly increased(P＜0.05);the content of UDP-N-acetylglucosamine in the insulin resistance pathway was significantly decreased in the IR70 group compared with the IR40 group(P＜0.05);the ergocalciferol content in the steroid biosynthesis pathway was significantly increased(P＜0.05);the testosterone content in the endocrine resistance pathway was significantly increased(P＜0.05);the O-phosphate-L-serine content in the glycine,serine and threonine metabolic pathways was sig-nificantly decreased(P＜0.05);UDP-N-acetylglucosamine content was significantly reduced in the neomycin,kanamycin and gentamicin biosynthetic pathways(P＜0.05);in the steroid hormone biosynthetic pathway,corticosterone and testosterone contents were significantly increased(P＜0.05).In summary,it is concluded that when suckling yak calves are bred by milk replacer feeding,increasing the amount of solid feed improve the quality of growth and development of yak calves,and promote the development of the morphology and function of their pancreatic tissues;and the medium feeding amount can induce the differentiation of pancreatic cells in suckling yak calves,and enhance the body's ability to digest and absorb small molecule nutrients.[Chi-nese Journal of Animal Nutrition,2023,35(12):7903-7919]
suckling periodyak calvesfeeding level of solid feedpancreas developmentmetabolomics
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