Research On The Nutrient Utilization Characteristics And Requirements Of Energy And Protein In Alpine Merino Lactating Ewes

Alpine Merino sheep,a new cultivated breed of wool-meat dual purpose,have strong adaptability to high altitude and arid ecological region of Qinghai Tibet Plateau in China.The experiment was conducted to explore the nutrient utilization of Alpine Merino lactating ewes and establish a prediction model of energy and protein requirements.Twenty-one 3-year lactating ewes（41.6±3.49 kg）given birth at the same day and single male lamb were selected from Alpine Merino core ewes group,and randomly divided into 3 groups with seven sheep in each group according to 3feeding levels:ad libitum（AL group）,80%of ad libitum（80%group）and 60%of ad libitum（60%group）.Digestion and metabolism experiments and respiration calorimetry experiments were carried out in the early（Lactating 1 to 40 d）,middle（Lactating 41 to 70d）and late lactation（Lactating 71 to 100 d）.Results as following shown:1.During the whole lactation period,dry matter（DM）,organic matter（OM）,neutral detergent fiber（NDF）and acid detergent fiber（ADF）intake,fecal excretion and digestibility,and gross energy intake（GEI）,fecal energy（FE）,digestible energy（DE）,metabolizable energy（ME）,heat production（HP）,CO₂ output,nitrogen intake（NI）,urinay nitrogen（UN）and digestible nitrogen（DN）decreased significantly with the decrease of feeding level（P<0.05）.The apparent digestibility of DM,OM,crude protein（CP）,NDF and ADF was not significantly affected by feeding level（P>0.05）,the apparent digestibility of DM during the early,middle and late lactation were60.58%～64.46%,61.33%～64.55%and 55.97%～58.79%;the apparent digestibility of OM were 66.84%～68.31%,65.08%～68.17%and 60.00%～62.61%;the apparent digestibility of CP were 80.42%～83.94%,73.23%～80.71%and 67.64%～69.88%;the apparent digestibility of NDF were 50.92%～52.47%,45.44%～50.65%and38.57%～43.51%;the apparent digestibility of ADF were 35.98%～40.15%,33.17%～39.92%and 38.71%～57.22%;ME/DE were 81.35%～87.26%,84.31%～86.85%and 80.28%～82.55%;apparent nitrogen digestibility were 82.61%～84.36%,73.23%～80.42%and 67.64%～69.88%,respectively.2.Feeding level and lactation period had no significant effect on the feed to weight ratio of ewes（P>0.05）;the milk yield of ewes decreased with the extension of lactation,during the early and middle lactation,the change trend of lactating ewes at different feeding levels was 60%group<AL group<80%group（P<0.05）.Feeding level and lactation period had significant effects on ruminal fluid p H,acetate,butyrate,valerate and isobuyrate molar ratio of Alpine Merino lactating ewes（P<0.05）,but had no significant effects on ruminal fluid NH₃-N,TVFA and the ratios of propionate,isovalerate and acetate to propionate in the rumen of ewes（P>0.05）.3.The prediction models of total net energy requirement（NE_m+NE_g）and total metabolizable energy requirement（ME_m+ME_g）of Alpine Merino lactating ewes are as follows:Early lactation:NE_m=303.18 KJ·kg^-1BW^0.75·d^-1,the prediction equation of NE_grequirement was log₁₀RE=3.22（±0.292）+0.471（±0.179）log₁₀BW;ME_m=357.07KJ·kg^-1BW^0.75·d^-1,the prediction equation of ME_g requirement was RE=-3.151（±0.899）+0.758（±0.145）MEI_g;K_m=NE_m/ME_m=0.85.Middle lactation:NE_m=299.50 KJ·kg^-1BW^0.75·d^-1,the prediction equation of NE_g requirement was log₁₀RE=3.15（±0.481）+0.465（±0.292）log₁₀BW;ME_m=373.49 KJ·kg^-1BW^0.75·d^-1,the prediction equation of ME_g requirement was RE=179.208（±64.698）+0.776（±0.108）MEI_g;K_m=NE_m/ME_m=0.80.Late lactation:NE_m=293.29 KJ·kg^-1BW^0.75·d^-1,the prediction equation of NE_grequirement was log₁₀RE=2.91（±0.732）+0.562（±0.112）log₁₀BW;ME_m=373.49KJ·kg^-1BW^0.75·d^-1,the prediction equation of ME_g requirement was RE=13.193（±31.653）+0.998（±0.068）MEI_g,K_m=NE_m/ME_m=0.80.4.The prediction models of total net protein requirement（NP_m+NP_g）of Alpine Merino lactating ewes are as follows:Early lactation:NP_m=2.463 g·kg^-1BW^0.75·d^-1,NP_g requirement prediction equation was log₁₀RN=-2.679（±1.007）+2.451（±0.601）log₁₀BW.Middle lactation:NP_m=2.214 g·kg^-1BW^0.75·d^-1,NP_g requirement prediction equation was log₁₀RN=-2.440（±0.967）+2.266（±0.577）log₁₀BW.Late lactation:NP_m=2.052 g·kg^-1BW^0.75·d^-1,NP_g requirement prediction equation was log₁₀RN=-2.277（±0.811）+2.051（±0.467）log₁₀BW.In conclusion,the protein and energy requirements of Alpine Merino ewes during lactation are different from those recommended by NRC,and the maintenance requirements are slightly higher,which is directly related to their living alpine enviroment.The model parameters and corresponding recommended values should be verified and improved in further production practice.