Research On Response And Mechanism Of Yak’s Rumen Metabolism And Nutrient Utilization To Dietary Nitrogen Levels

This study was conducted to set four dietary nitrogen levels, which were 6.45%,12.18%, 17.81% and 23.49% of crude protein on dry matter (DM) basis respectively, to research the effects of different dietary nitrogen levels on Tibetan Plateau yak rumen fermentation characteristics, nutrient utilization, urine PD excretion, and use urine PD method to estimate rumen microbial protein production. A 4×4 Latin square design was conducted. Four 3-year-old (BW=192±12kg)healthy, castrated yaks were randomly divided into four groups. There are four periods during the experiment, twenty-one days per period, including adjustment period of fifteen days and trying period of six days, all feces and urine were collected in digestibility and metabolism experiment. The diet was divided into concentrate and roughage, the concentrate in four groups had the same NDF and metabolism energy, but inconsistent nitrogen levels. The roughage was barley straw. The results were as in following content:1、Ruminal pH was significantly affected by the feeding time (P<0.05), the trendline falls first and rises then like V type after feeding, but not affected by nitrogen levels (P>0.05). The components of isobutyric and isovaleric were affected significantly by nitrogen levels (P<0.05), the rest of components of VFA and acetate/propionate were not affected (P>0.05). With the increase of N level, MN was also on increase significantly (P<0.01).The largest MN was 267.81g/d in 17.81% N. The innovation of this research was to optimize relationship between MN and purine intake (X, mmol/d): MN=70X/(0.12×0.83×1000)=0.703X (Low N feeding) MN=70X/(0.12×0.83×1000)=0.703X (Low-medium N feeding) MN=70X/(0.15×0.83×1000)=0.562X (High-medium N feeding) MN=70X/(0.19×0.83×1000)=0.444X (High N feeding)In above equations, N content of purine was 70mg/mmol and purine digestibility was 0.83.0.12 or 0.19 were the ratio of purine N to total N in rumen microbes.2、With the increase of dietary N level, total N intake, digestible-N intake, MN, N in urine, urine urea-N, N retention increased significantly (P<0.01).Dietary nitrogen levels had no significantly effect on N in feces and N retention ratio (P> 0.05)3、With the increase of dietary N level, the crude protein (CP) significantly increased (P <0.01), while dietary N level had no significant effects on organic matter (OM), dry matter (DM), acid detergent fibre (ADF), neutral detergent fibre (NDF) (P>0.05).4、There were two mainly substances of PD in yaks urine, allantoin and uric acid.With the increase of N level, there was a significant influence on the excretion of allantoin and uric acid (P <0.05)-As the high concentration, non-PD substance cretinnine and hippuric acid in this experiment also showed. Model established between N retention and PD, PD excretion(mmol/d)2、With the increase of dietary N level, total N intake, digestible-N intake, MN, N in urine, urine urea-N, N retention increased significantly (P<0.01).Dietary nitrogen levels had no significantly effect on N in feces and N retention ratio (P> 0.05)3、With the increase of dietary N level, the crude protein (CP) significantly increased (P <0.01), while dietary N level had no significant effects on organic matter (OM), dry matter (DM), acid detergent fibre (ADF), neutral detergent fibre (NDF) (P>0.05).4、There were two mainly substances of PD in yaks urine, allantoin and uric acid.With the increase of N level, there was a significant influence on the excretion of allantoin and uric acid (P <0.05)-As the high concentration, non-PD substance cretinnine and hippuric acid in this experiment also showed. Model established between N retention and PD, PD excretion(mmol/d)=106.34×N retention(g/Kg BW0.75/d)+22.104 (n=16;R2=0.9754), the estimation of endogenous PD excretion was 0.41 mmol/(Kg BW0.75.d)...