| Yak is the dominating animal in qinghai-tibet plateau,which has important influence on local politics,economy and culture.The hunger of yaks in cold season is an unavoidable problem in production and compensatory growth has great potential for pasture systems of yaks.Therefore,6 healthy yaks of which initiate average body weight were 183.60±15.62 kg were selected for this experiment.The experiment divided into three periods including normal feeding period(NFP,1 week),starvaton period(SP,1 week),and refeeding period(NFP,4 weeks).The growth performance,nutritional digestibility,blood indexes and rumen microorganism of yaks were determined.Results showed as follows:(1)Yaks lost 10.06% of initial weight after one-week starvation.The ratio of feed to gain and dry matter intake were remarkably decreased(P<0.05)in the first three weeks and average daily gain was notably increased(P<0.05)in the first two weeks.Apparent digestibility of crude protein,ether extract and crude fibre were improved(P<0.05)in the first week and then its went down.By week four,apparent digestibility of crude protein,ether extract and crude fiber return to normal level(P>0.05).(2)Serum glucose,triglyceride,urea nitrogen,and creatinine were remarkably decreased(P<0.05)and non-esterified fatty acid was significantly increased(P<0.05)in starvation period.Serum glucose,triglyceride,urea nitrogen,and creatinine were remarkably lower(P<0.05)in the first three weeks of refeeding period than that in normal feeding period.Non-esterified fatty acids and total protein were notably risen(P<0.05).The metabolites of serum had no notable difference(P>0.05)in refeeding-forth week with that in normal feeding period.(3)The concentrations of insulin,growth hormone,insulin-like growth factor ?,leptin,thyroid hormone,and cortisol were dramatically reduced(P<0.05)and adiponectin was notably increased(P<0.05)in starvation period.Serum insulin-like growth factor ? was remarkably elevated(P<0.05)in the refeeding period and serum cortisol was lower(P<0.05)than that in normal feeding period.The difference in hormone secretion mainly occurred in the first 3 weeks of refeeding period,and there was no significant difference of serum hormones in the fourth week with that in normal feeding period apart from adiponectin(P>0.05).(4)During starvation,the content of serum antioxidant enzymes,glutathione peroxidase and superoxide dismutase were significantly lower than the normal feeding period(P<0.05).The pro-inflammatory factor interleukin-1 ? and endotoxin was significantly lower(P<0.05)than the normal feeding period.The glutathione peroxidase,superoxide dismutase and malondialdehyde were significantly higher(P<0.05)in week 2 of refeeding period than in the normal feeding period,and the endotoxin were significantly lower(P<0.05)in week 1 and 3.At week 4,apart from interleukin-1 aspirate was significantly lower than the normal feeding period(P<0.05),other indicators had not significantly difference(P>0.05)with the normal feeding period.(5)A significant rise(P<0.05)of rumen pH and butyric acid showed up,and a notable decrease(P<0.05)of ammonia nitrogen,microbial protein,acetic acid,propionic acid,and endotoxin appeared in the starvation period.In the first three weeks of refeeding,rumen pH,ammoniacal nitrogen,endotoxin,and the ratio of acetic acid to propionic acid were significantly lower(P<0.05)than normal feeding period.The concentration of microbial protein,acetic acid and propionic acid were remarkably higher(P<0.05)than normal feeding period.There was no significant difference(P>0.05)between the pH,microbial protein,acetic acid,propionic acid and endotoxin in week four with the normal feeding period.(6)In the starvtion period,the observed species index of rumen microbial alpha diversity decreased significantly(P<0.05),the microbial community of in the starvation period was significantly different(P<0.05)with normal feeding period.The abundance of protein-utilizing bacteria,fat-using bacteria,butyrate producing bacteria,harmful bacteria and recombinant bacteria significantly increased(P<0.05),the archaea and the methanobacterium significantly decreased(P<0.05)in the starvation period,and the methane micrococcus significantly higher(P<0.05)than normal feeding period.The change of microorganism in refeeding period occurred mainly in the first week.The observed species index of rumen microbial alpha diversity was notably lower(P<0.05)than normal feeding period.The microbial community of in the starvation period was significantly different(P<0.05).The abundance of propionic acid producing bacteria was significant higher than normal feeding period(P<0.05).In the first 3 weeks,the abundance of methanogenic archaea was significantly lower(P<0.05).than normal feeding period,and the composition of rumen microorganism in the second,third and fourth weeks had not significantly difference(P>0.05)with normal feeding period.To sum up,yaks adapt to starvation by losing weight,increasing fat mobilization,decreasing growth-related hormone secretion,antioxidant capacity and rumen microbial fermentation.Compared with the normal feeding period,the structure of rumen bacteria in yak is significantly changed by refeeding after feed restriction,the abundance of propionic acid producing bacteria and the concentration of propionic acid are increased,propionic acid fermentation is promoted,the abundance of methanogenic archaea is reduced,microbial protein synthesis and rumen fermentation are improved.At the same time,refeeding increase the secretion of IGF-? and the apparent digestibility of crude protein,crude fat,crude fiber.Nutrition metabolism of yaks is improved by refeeding,thus accelerate the growth of yak.The compensatory growth effect mainly occurred in the first 3 weeks,in 4th week of refeeding,the growth of yaks was at the same level as the normal feeding period. |
PDF Full Text Request