Tannins are phenolic compounds that provide benefits to ruminants due to their protein-binding affinities and antioxidant properties. However, tannins may also have negative orosensorial and postingestive effects that decrease feed intake. This study explored how lambs trade-off the ingestion of crude protein (CP) with the ingestion of potentially beneficial and toxic condensed and hydrolyzable tannins, and the ensuing impacts on diet digestibility, animal performance, and blood parameters. Thirty-two lambs were housed in individual pens for 8 weeks and had access to two isoenergetic diets that varied in the concentration of CP (High-HP or Low-LP) and the presence of a mix of condensed and hydrolyzable tannins (4% DM). Animals were assigned to 4 treatment groups (N=8 lambs/group) and received a simultaneous offer of: HP and LP (Control); HP and LP+tannins (HP-LP+); HP+tannins and LP (HP+LP-); and both HP and LP with tannins (HP+LP+). All lambs preferred HP over LP and they avoided tannins in the diets (P < 0.001). Dry matter and CP intake were the lowest in HP+LP- (P < 0.0001), and DMD did not differ between Control and the other groups (P > 0.05), but it was greater for HP-LP+ (P < 0.0001). Crude protein digestibility was greater for groups without tannins in HP (P < 0.0001), but ADG did not differ among treatments (P > 0.05). No differences between Control and HP+LP+ were found in plasma antioxidant activity, total phenolic concentration, or haptoglobin concentration (P > 0.05). Intake of tannins was HP+LP+ > HP+LP- > HP-LP+ (P < 0.0001), and fecal excretion of nitrogen (N) was HP+LP+ > HP-LP+ = HP+LP- > Control (P < 0.05). In addition, intake of tannins with both diets reduced blood urea nitrogen (BUN) concentration relative to Control (P < 0.05), thus suggesting a shift in the partitioning of N excretion from urine to feces. In summary, lambs prioritized selection of HP over LP, regardless of the presence of a tannin extract in either or both diets. Nevertheless, lambs modulated their tannin consumption as a function of the specific diet where the tannin extract was added, with increasing levels of intake as tannins were present in just LP, then in just HP, and finally in both diets. Dietary tannins did not constrain ADG and resulted in a shift in the partitioning of N excretion from urine to feces. Such shifts have been found to result in reduced production of environmental pollutants such as ammonia, nitrous oxide, and nitrates.

中文翻译：

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生长羔羊中粗蛋白和单宁选择之间的权衡


单宁是酚类化合物，由于其蛋白质结合亲和力和抗氧化特性，为反刍动物带来益处。然而，单宁也可能具有负面的口腔感应和摄入后影响，从而降低采食量。本研究探讨了羔羊如何在摄入粗蛋白 （CP） 与摄入可能有益且有毒的缩合和可水解单宁之间进行权衡，以及随之而来的对饮食消化率、动物生产性能和血液参数的影响。32 只羔羊被饲养在单独的围栏中 8 周，并获得了两种等能饮食，这两种日粮的 CP 浓度（高 HP 或低 LP）以及缩合和可水解单宁混合物 （4% DM） 的存在各不相同。将动物分配到 4 个治疗组 （N=8 只羔羊/组） 并同时接受以下提议：HP 和 LP （对照）;HP 和 LP+单宁 （HP-LP+）;HP+单宁和 LP （HP+LP-）;以及带有单宁的 HP 和 LP （HP+LP+）。所有羔羊都喜欢 HP 而不是 LP，它们避免在日粮中使用单宁 （P < 0.001）。HP+LP- 干物质和 CP 摄入量最低 （P < 0.0001），对照组与其他组 DMD 无差异 （P > 0.05），但 HP-LP+ 的干物质摄入量较高 （P < 0.0001）。HP 中单宁无组的粗蛋白消化率较高 （P < 0.0001），但 ADG 在不同处理间没有差异 （P > 0.05）。对照组和 HP+LP+ 在血浆抗氧化活性、总酚浓度或结合珠蛋白浓度方面没有差异 （P > 0.05）。单宁摄入量为HP+LP+ > HP+LP- > HP-LP+（P < 0.0001），粪便氮（N）排泄量为HP+LP+ > HP-LP+ = HP+LP- >对照（P < 0.05）。 此外，相对于对照，两种饮食中单宁的摄入量降低了血尿素氮 （BUN） 浓度 （P < 0.05），因此表明 N 排泄从尿液到粪便的分配发生了变化。总之，羔羊优先考虑选择 HP 而不是 LP，无论其中一种或两种日粮中是否存在单宁提取物。然而，羔羊根据添加单宁提取物的特定饮食调节了它们的单宁消耗，随着摄入量的增加，因为单宁仅存在于 LP 中，然后仅存在于 HP，最后存在于两种日粮中。膳食单宁不限制 ADG，并导致 N 排泄从尿液到粪便的分配发生变化。已发现这种转变会导致氨、一氧化二氮和硝酸盐等环境污染物的产生减少。