| Tibetan sheep,with a population of over 50 million,are one of the most widespread domesticated animals on the Qinghai–Tibetan Plateau and have played an essential role in the maintenance of the environment-grassland-livestock and human settlement system on the Qinghai-Tibet Plateau?QTP?.However,due to the unique climate environment of low temperature,hypoxia and high altitude,there is little information available to systematically study the nutrients digestion and metabolism of Tibetan sheep under grazing and other management methods,especially on the characteristics of enteric methane emissions.The objective of the present study were to identify the seasonal characteristics of nutrients digestive metabolism and enteric methane emission of Tibetan sheep under continuous grazing,zero grazing,grazing with supplementary,and feedlot feeding.The main results are as follows:1.The seasonal dynamics of nutrients digestion,metabolism of Tibetan sheep under continuous grazingThe dry matter intake per unit metabolic body weight(DMI/LW0.75)and crude protein intake?CPI?of Tibetan sheep in warm season were 3.5 times and 7.9 times higher than those in cold season,respectively.Tibetan sheep had higher apparent dry matter digestibility?DMD?,organic matter digestibility?OMD?,crude protein digestibility?CPD?,neutral detergent fiber digestibility?NDFD?,acid detergent fiber digestibility?ADFD?,digestible energy?DE?and metabolic energy?ME?in warm season,which were 15%,19%,6%?18%,14%,39%and 34%higher than those in cold season,respectively.2.Effects of zero grazing and barn feeding oat hay on nutrients digestion,metabolism and enteric methane emission.In the warm season,the dry matter intake per unit metabolic body weight(DMI/LW0.75)and crude protein intake were higher for zero grazing than oat hay–fed Tibetan sheep.But DMD,DE,ME and retained nitrogen were lower for zero grazing than oat hay-fed Tibetan sheep.Enteric CH4 emission and gross energy losses in CH4,were 11%and 5%less by oat hat-fed than by zero grazing Tibetan sheep,respectively.In cold season,the oat hay fed?50%?sheep showed significant higher?P<0.05?the dry matter intake,nutrients digestion and metabolism and retained nitrogen compared to zero grazing and barn feeding sheep.Compared to other treatments,oat hay fed?50%?sheep had significant?P<0.05?lower enteric CH4 emission rate.Under the management modes of zero grazing,oat hay barn feeding and oat hay supplementary feeding,the daily enteric CH4 emissions of Tibetan sheep were 23.89g/head,18.62 g/head and 17.82 g/head,respectively.The zero grazing Tibetan sheep had higher dry matter intake per unit metabolic weight(DMI/LW0.75)and crude protein intake?CPI?in warm season than in cold season.The DMD,DE,ME and retained nitrogen in warm season were 17%,23%,17%and 38%higher?P<0.05?than those in the cold season,respectively.CH4 emission and gross energy losses in CH4in the warm season were 44%and 50%lower than those in the cold season,respectively.There were no significant differences in dry matter intake,energy utilization efficiency,nitrogen metabolism and enteric methane emissions among the experimental years?P>0.05?.However,significant interannual and seasonal interactions on the dry matter intake,nutrients digestion,metabolism and enteric methane emissions were observed under the zero-grazing treatment?P<0.001?.3.Effect of oat hay supplementary feeding on the slaughter performance and mutton qualityIn cold season,oat hay supplementation had no effects on slaughter body size of Tibetan sheep?P>0.05?,but the oat hay feeding?50%?enhanced?P<0.05?the slaughter rate and carcass weight.There were no significant difference in eye muscle area,GR value and flower oil.Besides,oat hay supplementary feeding in cold season significantly increased the content of protein and ash and decreased the content of fat in meat,but had no significant effect on the meat tenderness,cooked meat rate,amino acid type and content in mutton.4.Prediction models for herbage energy and methane emission of grazing Tibetan sheepA series of prediction models for evaluation of forage digestible energy?DE?and metabolizable energy?ME?contents were constructed based on the nutrient composition and digestibility of herbage in alpine meadow.Dry matter digestibility?DMD?,organic matter digestibility?OMD?,digestible organic matter digestibility?DOMD?and grass energy digestibility?GED?were used to estimate the ME and DE content with higher prediction accuracy.The best predictor for Tibetan sheep CH4 production is dry matter intake?R2=0.780,SE=2.17?,It had higher prediction accuracy for Tibetan sheep CH4 production when using DMI alone or using DMI as primary predictor and forage nutrients contents?DM,OM,NDF,ADF,GE,Ash,N,WSC,and EE?as supporting predictors?P<0.01?.In general,the Tibetan sheep had higher nutrients digestion,metabolism,nitrogen and energy utilization efficiency in the warm season than those in the cold season.The methane emission factors from free grazing,zero grazing and supplementary feeding in the current study could be used to predict CH4 emissions for Tibetan sheep in the Qinghai-Tibet Plateau. |
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