Effects Of Dietary Energy Levels On Rumen Nitrogen Transportation And Utilization In Tibetan Sheep

As a unique livestock of the Qinghai-Tibet Plateau,Tibetan sheep have formed a unique adaptive mechanism to cope with the harsh stress of local harsh environment and nutrient deficiency after long-term natural and artificial selection,especially for the lack of nitrogen.However,in reality,Tibetan sheep are still limited by nutrient deficiencies during the cold season,which seriously restricts the reproduction and production performance of Tibetan sheep.The aim of this study was to explore the effects of low nitrogen diet under different energy levels on rumen nitrogen transport and utilization in Tibetan sheep.and than reveals the special adaptation mechanism of Tibetan sheep to adapt to alpine nutrient stress,to impart a theoretical basis and data support for the appropriate energy and nitrogen supplementation technology for Tibetan sheep in the cold season,Thereby achieving the development of high-altitude animal husbandry.Experiment 1 Effects of dietary energy levels on nutrient utilization,rumen fermentation and Purine Derivatives of Tibetan sheep and Small tailed Han sheepHealthy castration male Tibetan sheep(n=5)and Small tailed Han sheep(n=5)of 1.5 years old with similar body weight(47.7±2.46 kg,46.2±3.42 kg)were selected in 2 concurrent 4×4 Latin square designs.(one of the sheep as replicate).Comparing the growth performance,rumen fermentation and nitrogen utilization with different energy levels(digestible energy: 8.21 MJ/kg,9.33 MJ/kg,10.45 MJ/kg,11.57 MJ/kg)on Tibetan sheep and Small tailed Han sheep under low nitrogen diet.The results showed as following:(1)The apparent digestibilities of DM,OM,CP,NDF,ADF and GE were greater(P<0.05)in Tibetan than in Han sheep.As dietary energy level increased,DM%,OM%,ash% and GE increased linearly(P<0.01);and of NDF% and ADF% decreased linearly(P<0.01).CP% increased linearly with an increase in energy intake in Tibetan sheep but remained stable in Han sheep(linear dietary energy × breed,P<0.05).The average daily weight gain(ADG)of the Tibetan sheep was significantly higher than that of the small tail Han sheep(P<0.01),and both of them increased linearly with the increase of dietary energy under the nitrogen stress condition(P<0.01),When the dietary energy is in the MLE level,the ADG of Tibetan sheep is positive,but the Han sheep is still negative.(2)Number of white blood cells(WBC),red blood cell(RBC),hemoglobin(HGB),hematocrit(HTC)and platelet(PLT)were significantly lower than that of Han sheep(P<0.05),the WBC,RBC,HGB and HTC decreased significantly and the PLT increased significantly with the increase of dietary energy levels(P<0.01).Serum GH concentration tended to be lower in Tibetan than in Han sheep(P=0.057).As dietary energy increased,the concentrations of GLU,INS,and IGF-1 increased linearly(P <0.05),while of NEFA and GH decreased linearly(P<0.05).(3)Total ruminal VFA concentrations were greater(P<0.05)while pH was lower(P<0.05)in Tibetan than in Han sheep.As dietary energy increased,the proportions of propionate,butyrate and iso-acids increased linearly(P<0.05),whereas the proportion of acetate decreased(P<0.001),accompanied with a decreased tendency of acetate to propionate ratio(P=0.078).Ruminal ammonia-N,urea-N and soluble protein-N concentrations were greater in Tibetan than in Han sheep(P<0.05),As dietary energy increased,ruminal urea-N,ammonia-N and free amino acid-N decreased linearly(P<0.01).Ruminal soluble protein-N increased linearly with dietary energy in Tibetan sheep while it remained constant in Han sheep(linear dietary energy × breed,P<0.05).Rumen microbial protein-N concentration increased linearly as dietary energy increased(P<0.001),and the incremental rate was greater in Tibetan than in Han sheep(linear dietary energy × breed,P <0.01).(4)Urinary elimination of total PD,and Microbial nitrogen synthesis efficiency(MN/NI)were greater in Tibetan than Han sheep(P<0.01),As dietary energy increased,total PD,Microbial N production and Microbial nitrogen synthesis efficiency(MN/NI)increased linearly(P<0.05).Experiment 2 Effects of dietary energy levels on the expression of aquaporin 3(AQP3)mRNA and protein in rumen and kidney tissues of Tibetan sheep and Small tailed Han sheepHealthy castration male Tibetan sheep(n=24)and Small tailed Han sheep(n=24)of 1.5 years old with similar body weight(48.5±1.89 kg;49.2±2.21 kg)were selected for this study,randomly divided into four treatment groups,and the dietary energy level was the same with the experiment 1.Real-time quantitative PCR(qRT-PCR)and Western blot(Western blot)were used to study the effects of dietary energy levels on the expression of AQP-3 mRNA and protein under low nitrogen conditions.The results showed as following:(1)The abundance of AQP3 mRNA expression in rumen dorsal sac and caudo-dorsal sac of Tibetan sheep was significantly higher than that of Han sheep(P<0.05).As dietary energy increased,the abundance of AQP3 mRNA expression in rumen dorsal sac,rumen ventral sac,renal cortex and renal medulla were increased linearly(P<0.05).(2)The abundance of AQP3 protein in rumen dorsal sac of Tibetan sheep was significantly higher than that of Han sheep(P<0.01).As dietary energy increased,the rumen dorsal sac,renal cortex and renal medulla were linearly increased(P<0.01),while the rumen abdominal sac was linearly decreased(P<0.01).In general,Increasing the energy level of the diet can effectively improve the growth performance and nitrogen utilize efficiency.Compared with Han sheep,Tibetan sheep showed stronger feed digestion capacity and higher VFA yield to provide more energy for metabolism;higher rumen microbial protein synthesis and effective participation in urea transport carrier AQP3 regulation to increase nitrogen utilize efficiency to compensate for the lack of nitrogen in the diet.