Study on the protein digestion and nitrogen metabolism of horses fed high-roughage diets

本试验选用装有回肠内套管的北海道土生马，研究1)日粮蛋白质含量对马氮代谢的影响。随着蛋白质摄入量的增加，尿素在体内的合成和从体内向消化道的转移以及尿中尿素的排泄量都增加。当蛋白质摄入量减少时，大部分从体内转移到消化道的氮被用于尿素的再合成。这说明在蛋白质摄入量减少的情况下，尿素向消化道的转移有利于尿素的利用。2)日粮蛋白质含量对马后肠发酵和饲料利用的影响。粗蛋白质消化率和蛋白质积累率随蛋白质摄入量的增加而提高。后肠总VFA和NH3-N浓度也有升高趋势，pH值有下降趋势。随着日粮蛋白质水平的提高，蛋白质在小肠中的消化率增加。然后，进入后肠的氮素流量增加。NDF和ADF的消化率以及尿中DAPA的浓度不受日粮蛋白质水平的影响。3)将NH3-N转移到血浆中的氨基酸注入回肠，将标记为^&lt；15&gt；N的氨注入软管的回肠，以研究内源性氨转移到消化道的去向。结肠中的所有细菌氨基酸-N都含有约1%的N-N。血浆中的游离必需氨基酸，如亮氨酸、赖氨酸、Val、组氨酸、赖氨酸、苯丙氨酸的含量较高，说明血浆中的部分氨基酸来源于肠道细菌合成的氨基酸。

Hokkaido native horses fitted with the cannulae in the endo of ileum were used in this study.1) Effect of dietary protein contents on nitrogen metabolism of horses. Urea synthesis in the body and its transfer to digestive tract from the body, and urinary excretion of urea were increased with increasing protein intake. When protein intake was decreaed, most of nitrogen that transferred to digestive tract from the body were utilized for urea re-synthesis. This suggested that urea transfer to digestive tract made a contribution to urea utilization of horses, when protein intake was decreased.2) Effect of dietary protein contents on feed utilization and fermentation of hindgut of horses. Crude protein digestibility and the rate of protein accumulation was increased with increasing protein intake. Total VFA and NH_3-N concentrations in the hindgut was also increased, whereas pH tended to be decreased. When dietary protein level was increased, protein digestibility in the small intestine was increased. Then, nitrogen flow into the hindgut was increased. NDF and ADF digestibilities, as well as DAPA concentration in urine were not affected by dietary protein levels.3) Transfer into plasma amino acids from NH_3-N infused into the ileum of horses Ammonia labelled ^<15>N was infused into the ileum of hoses in order to investigate the fate of endogeneous ammonia translated into digestive tract. All bacterial amino acid-N in the colon contained about 1% of ^<15>N-nitrogen. Free essential amino acids in plasma, such as leu, ile, val, his, lys, phe, had higher ^<15>N. This suggested that a part of plasma amino acids originated from amino acids synthesized by bacteria in the colon of horses.