Zinn R A, Barreras A, Corona L, Owens F N, Ware R A
Department of Animal Science, University of California, Davis, CA 95616, USA.
J Anim Sci. 2007 Jul;85(7):1727-30. doi: 10.2527/jas.2006-556. Epub 2007 Mar 30.
To evaluate the utility of N as a digestion marker to predict total tract starch digestion, data from 32 metabolism trials involving 147 steers and 637 individual starch digestibility measurements were compiled. All trials were conducted at the University of California Desert Research and Extension Center. Total tract starch digestibility was determined from concentrations of starch and chromic oxide in feed and feces. In all trials, the steers were adapted to diets for 10 d followed by 4 d for collection of samples of feces. During collection, fecal samples (approximately 200 g, wet basis) were obtained twice daily. Samples from each steer within each collection period were composited for analysis. Diets contained 46.5 +/- 7.4% starch and 1.85 +/- 0.20% N. Apparently digestible N as a percentage of diet DM was closely associated (r(2) = 0.73; P < 0.001) with dietary N concentration. Fecal N concentration (FN, % of DM) explained 35% of the variation in fecal DM excretion (S(y.x) = 4.3; P < 0.001). Incorporating FN into the model, starch digestion was estimated as follows: starch digestion, % of intake = 100 {1 - [(0.938 -0.497FN + 0.0853FN(2)) FS/DS]}, where FS is fecal starch concentration (% of DM) and DS is dietary starch concentration (% of DM; r(2) = 0.94; S(y.x) = 0.68; P < 0.001). Fecal starch concentration alone explained 96% of the variation (S(y.x) = 0.45; P < 0.001) in total tract starch digestion: starch digestion, % = 99.9 - 0.413FS -0.0104FS(2). Omitting cases in our data set in which observed total tract starch digestion was less than 95%, the r(2) between FS and starch digestibility decreased to 0.82 (S(y.x) = 0.26; n = 529). However, estimated starch digestion using the equation incorporating FN remained closely associated with the observed starch digestion (r(2) = 0.90; S(y.x) = 0.22; P < 0.001; n = 529). Equations also were developed to predict NE(m) and NE(g) concentrations of common feed grains based on starch digestibility and FS. Starch digestion can be accurately predicted based on FS. However, incorporation of FN into the model markedly enhanced the estimates of grain quality and the efficacy of processing when total tract starch digestion exceeded 95%.
为评估氮（N）作为消化标志物预测全消化道淀粉消化率的效用，收集了来自32项代谢试验的数据，这些试验涉及147头阉牛以及637次个体淀粉消化率测定。所有试验均在加利福尼亚大学沙漠研究与推广中心进行。全消化道淀粉消化率通过饲料和粪便中淀粉及氧化铬的浓度来测定。在所有试验中，阉牛先适应日粮10天，随后进行4天粪便样本采集。采集期间，每天两次获取粪便样本（湿基约200克）。每个采集期内每头阉牛的样本混合后进行分析。日粮含有46.5±7.4%的淀粉和1.85±0.20%的氮。表观可消化氮占日粮干物质的百分比与日粮氮浓度密切相关（r² = 0.73；P < 0.001）。粪便氮浓度（FN，占干物质的百分比）解释了粪便干物质排泄量变化的35%（估计标准误差S(y.x) = 4.3；P < 0.001）。将FN纳入模型后，淀粉消化率的估计如下：淀粉消化率（占摄入量的百分比）= 100×{1 - [(0.938 - 0.497FN + 0.0853FN²)×粪便淀粉浓度（FS）/日粮淀粉浓度（DS）]}，其中FS是粪便淀粉浓度（占干物质的百分比），DS是日粮淀粉浓度（占干物质的百分比；r² = 0.94；S(y.x) = 0.68；P < 0.001）。仅粪便淀粉浓度就解释了全消化道淀粉消化率变化的96%（S(y.x) = 0.45；P < 0.001）：淀粉消化率（%）= 99.9 - 0.413FS - 0.0104FS²。在我们的数据集中剔除观察到的全消化道淀粉消化率低于95%的情况后，FS与淀粉消化率之间r²降至0.82（S(y.x) = 0.26；n = 529）。然而，使用纳入FN的方程估计的淀粉消化率与观察到的淀粉消化率仍密切相关（r² = 0.90；S(y.x) = 0.22；P < 0.001；n = 529）。还建立了基于淀粉消化率和FS预测常见饲料谷物净能（NE(m)）和净能（NE(g)）浓度的方程。基于FS能够准确预测淀粉消化率。然而，当全消化道淀粉消化率超过95%时，将FN纳入模型显著提高了谷物品质的估计以及加工效果。
