Nutrients intake of grazing sheep based on net flux of nitrogen and oxygen by splanchnic tissues

通过2年3个试验，研究了放牧绵羊能量摄入和氮代谢，以及门静脉引流脏器（PDV）和肝脏的氮净通量和氧消耗。在门静脉、肝静脉、肠系膜静脉和腹主动脉中长期留置导管的Wethers在限制喂养的情况下使用（Exp. 1和2）和放牧与随意摄入量（实验。3)条件实验试验1：绵羊日粮由粗饲料（70只）和精饲料（30只）组成，分为四个水平，维持能量（M）的0.5 ~ 1.76倍。绵羊消化能、氮摄入量和氮存留量随饲养水平的增加而线性增加。PDV对NH3-N的吸收也呈线性增加，而α-氨基N的吸收则从0.5M的零开始呈二次曲线增加。2：绵羊饲喂粗饲料（1.0M）和四种量的大麦补充物（0至1.0M）。消化能和氮的摄入量线性增加，但氮存留二次响应的补充水平。α-氨基氮的PDV释放量随饲料添加量的增加而线性增加，而总内脏组织（TSP）的α-氨基氮释放量由于肝脏摄取量的增加而几乎不变。增加的补充量线性增加了PDV对尿素氮的去除，但不影响肝脏对尿素氮的合成和PDVExp对氨氮的吸收。5月和6月，这些羊在牧场上吃草。添加大麦后，TSP释放的α-氨基氮增加，6月比5月减少。消化能摄入量，用实验中PDV耗氧量和能量摄入量之间的线性回归估计。1号和2号在6月份的产量较高，不受大麦补充的影响

The objectives were to investigate energy intake and nitrogen (N) metabolism of grazing sheep with net flux of N and oxygen consumption by the portal drained viscera (PDV) and liver through three experiments over two years. Wethers with chronic indwelling catheter in the portal, hepatic and mesenteric veins and the abdominal aorta were used under housing with restricted feeding (Exp. 1 and 2) and grazing with adlibitum intake (Exp. 3) conditionsExp. 1 : The sheep were fed a diet consisting of forage (70) and concentrate (30) at four levels, 0.5 to 1.76 times maintenance energy (M). Digestible energy and N intakes and N retention of sheep linearly increased with the feeding level. Ammonia N absorption by PDV also increased linearly, while α-amino N absorption, starting from null at 0.5M, increased quadraticallyExp. 2 : The sheep were fed forage (1.0M) plus four amounts of barley supplement (0 to 1.0M). Digestible energy and N intakes increased linearly, but N retention quadratically responded to the supplement level. The PDV release of α-amino N increased linearly with the supplement level, although the a -amino N release by the total splanchnic tissues (TSP) was almost constant due to the increase in the liver uptake. The increased supplement linearly increased the remove of urea N by PDV, but did not affect urea N synthesis by the liver and ammonia N absorption by PDVExp. 3 : The sheep were grazed on a pasture during May and June. The α-amino N release by TSP increased with barley supplement, and was less in June compared with May. Digestible energy intake, estimated with a linear regression between the PDV oxygen consumption and energy intake in Exp. 1 and 2, was greater in June, and not affected by barley supplement