Woodward A, Reed J D
International Livestock Centre for Africa, Addis Ababa, Ethiopia.
J Anim Sci. 1997 Apr;75(4):1130-9. doi: 10.2527/1997.7541130x.
We described the effects of two East African browses, Acacia brevispica and Sesbania sesban, on nitrogen metabolism of sheep and goats. The A. brevispica had a substantial amount of proanthocyanidins (condensed tannins); S. sesban did not. The browses were fed at three levels in combination with vetch (Vicia dasycarpa) and teff straw (Eragrostis abyssinica). Fecal N, N balance, and plasma urea N (PUN) were estimated with intact animals. Ruminal ammonia (RuA) and VFA concentrations were estimated with ruminally fistulated animals. Urinary N loss, PUN, RuA, and VFA concentrations were higher for S. sesban diets than for A. brevispica diets. Fecal N was highest with diets including A. brevispica due to high levels of fecal neutral-detergent insoluble N. Nitrogen retention was highest for diets including S. sesban. Nitrogen retention was adequate for A. brevispica diets because low urinary N compensated for high fecal N. Four hypotheses describe possible effects of tannins on N metabolism: 1) escape of protein from the rumen to the lower tract; 2) increased microbial yield; 3) increase in N-containing endogenous products; and 4) protein made indigestible in tannin-protein complexes. The effect of tannins in A. brevispica on N metabolism can best be described by the formation of indigestible tannin-protein complexes, although increased production of endogenous products is also possible.
我们描述了两种东非灌木——短尖相思树（Acacia brevispica）和塞内加尔田菁（Sesbania sesban）对绵羊和山羊氮代谢的影响。短尖相思树含有大量原花青素（缩合单宁）；塞内加尔田菁则不含。将这两种灌木与巢菜（Vicia dasycarpa）和画眉草秸秆（Eragrostis abyssinica）按三个水平混合投喂。通过完整动物估算粪便氮、氮平衡和血浆尿素氮（PUN）。通过瘤胃造瘘动物估算瘤胃氨（RuA）和挥发性脂肪酸（VFA）浓度。塞内加尔田菁日粮组的尿氮损失、PUN、RuA和VFA浓度高于短尖相思树日粮组。由于粪便中性洗涤不溶性氮含量高，含短尖相思树的日粮粪便氮含量最高。含塞内加尔田菁的日粮氮保留率最高。短尖相思树日粮的氮保留率足够，因为低尿氮补偿了高粪便氮。有四个假说来描述单宁对氮代谢的可能影响：1）蛋白质从瘤胃逃逸至下消化道；2）微生物产量增加；3）含氮内源性产物增加；4）单宁 - 蛋白质复合物使蛋白质难以消化。短尖相思树中单宁对氮代谢的影响最好用形成难以消化的单宁 - 蛋白质复合物来解释，不过内源性产物产量增加也有可能。
