Holland J L, Kronfeld D S, Sklan D, Harris P A
Virginia Polytechnic Institute and State University, Middleburg Agricultural Research and Extension Center, 20117, USA.
J Anim Sci. 1998 Jul;76(7):1937-44. doi: 10.2527/1998.7671937x.
Marker methods are needed for estimating fecal output by grazing animals in studies of nutrition and environmental impact. In addition, estimates of prefecal mass and turnover time are relevant to exercise performance and certain digestive disorders. As a first step in developing marker methods for field use, a chromic oxide model of fecal kinetics was developed and tested in the context of a digestion balance experiment with stall-fed horses. The model consists of removal of feces at a constant rate from a single compartment, the prefecal mass. Four horses were fed hay, and another four were fed hay and concentrate. Balance-marker experiments were conducted for 10 d, following 7 d of adaptation. A dose of chromic oxide mixed in chopped hay and molasses was administered from a nose bag at 0700 daily for 10 d. Dry matter and Cr were measured in feeds and feces. Fecal Cr concentration (C, mg/kg DM) varied during the day, so data from total daily collections were used for model development. These fecal Cr data (Ct) at time t (days) were fitted to a single exponential, with one rate constant (k), rising to an asymptote (Ca): Ct = Ca - Ca x e(-kt). Superior fits were obtained when a delay (d) was introduced between the pulse oral dose and the entry of marker into the prefecal pool: Ct = Ca - Ca x e(-k(t-d)). Using pooled data, delays of 2.7 and 2.0 h gave best fits (highest estimates of R2) for pooled data from horses fed hay or hay plus concentrate, respectively. The model generated estimates of 3.4 and 3.8 kg/d of DM for fecal outputs (dose/Ca) of horses fed hay or hay and concentrate, respectively. The rate constants yielded turnover times (1/k) of 33 and 18 h, and prefecal masses [(dose/Ca)/k] of 4.6 and 2.9 kg of DM for hay or hay and concentrate groups, respectively. Using data from individual horses, mean estimates for each diet were similar to corresponding values for the pooled data. In balance experiments, feces collected were 3.7 and 4.4 kg/d, and Cr recoveries were 108 and 115% dose for the hay and hay plus concentrate diets, respectively. Marker estimates (M) were correlated with total collection estimates (T) of fecal output [M = T(.890 +/- .045); r = .70, P = .041]. Adjusting for recovery improved the regression coefficient to 1.009 +/- .028 (r = .87, P = .002). The findings suggest that if Cr doses are more frequent than daily and if Cr inputs other than dose can be eliminated this method should give accurate and precise estimates of fecal output.
在营养和环境影响研究中，需要标记物方法来估算放牧动物的粪便排出量。此外，粪便前体质量和周转时间的估算与运动表现和某些消化系统疾病相关。作为开发适用于野外的标记物方法的第一步，在一项舍饲马的消化平衡实验中，开发并测试了粪便动力学的氧化铬模型。该模型包括以恒定速率从单个隔室（粪便前体质量）中清除粪便。四匹马喂干草，另外四匹马喂干草和精饲料。在适应7天后进行了为期10天的平衡标记物实验。每天0700从鼻袋中给马投喂混入切碎干草和糖蜜中的氧化铬剂量，持续10天。测定饲料和粪便中的干物质和铬。粪便铬浓度（C，mg/kg干物质）在一天中有所变化，因此使用每日总收集数据进行模型开发。这些在时间t（天）的粪便铬数据（Ct）拟合为单指数曲线，具有一个速率常数（k），上升至渐近线（Ca）：Ct = Ca - Ca x e(-kt)。当在脉冲口服剂量和标记物进入粪便前体池之间引入延迟（d）时，获得了更好的拟合：Ct = Ca - Ca x e(-k(t-d))。使用汇总数据，对于喂干草或干草加精饲料的马的汇总数据，延迟2.7小时和2.0小时分别给出了最佳拟合（R2的最高估计值）。该模型分别得出喂干草或干草和精饲料的马的粪便排出量（剂量/Ca）的干物质估计值为3.4和3.8 kg/d。速率常数得出周转时间（1/k）分别为33和18小时，干草或干草和精饲料组的粪便前体质量[（剂量/Ca）/k]分别为4.6和2.9 kg干物质。使用个体马的数据，每种饮食的平均估计值与汇总数据的相应值相似。在平衡实验中，干草和干草加精饲料饮食的粪便收集量分别为3.7和4.4 kg/d，铬回收率分别为剂量的108%和115%。标记物估计值（M）与粪便排出量的总收集估计值（T）相关[M = T(.890 +/- .045); r = .70, P = .041]。调整回收率后，回归系数提高到1.009 +/- .028（r = .87, P = .002）。研究结果表明，如果铬剂量比每日更频繁，并且如果可以消除除剂量之外的铬输入，这种方法应该能够准确精确地估算粪便排出量。
