One factor influencing the extent of feed degradation is the length of time feed resides at the site of digestion. Traditionally, mean retention time (MRT) is measured for the entire equine gastrointestinal tract (GIT), but retention time in specific organs may be more relevant to understanding digestion. Multi-compartment models theoretically partition the GIT to potentially represent MRT in individual segments. The objective of this study was to apply a multi-compartment model to digesta passage in horses fed forage-based diets. We hypothesized forage neutral detergent fiber concentration would alter total tract MRT, transit time (TT), and compartment retention time. Six geldings (4 ± 1.5 y, 545.0 ± 64.5 kg, mean ± SD) were randomly assigned a diet of timothy cubes (Hi NDF, n = 3) or alfalfa cubes (Lo NDF, n = 3) fed at 1.53% BW and concentrate at 0.22% BW (DM basis). After a 15-d dietary adaptation, geldings were orally dosed with Co-EDTA and Yb-labeled NDF residue to determine liquid and particulate retention time. A total fecal collection was conducted for 120 h after marker dosing. Samples were analyzed for Co and Yb concentrations by inductively coupled plasma spectrometry. Gamma distributed age-dependent two compartment models were fit to marker excretion curves for each gelding (MATLAB, vR2014a). Diet effects were analyzed by ANOVA (SAS, v9.3). There was no effect of diet on total tract MRT (liquid 21.78 ± 0.79 h, particulate 25.80 ± 0.79 h, mean ± SEM). However, liquid TT was longer (P = 0.041) in the Hi NDF diet (7.25 ± 0.91 h) than the Lo NDF diet (3.86 ± 0.91 h), and liquid age-dependent compartment retention time was shorter (P = 0.019) in the Hi NDF diet (8.40 ± 0.84 h) compared with Lo NDF diet (11.72 ± 0.84 h). Particulate TT was longer (P = 0.029) in the Hi NDF diet (8.24 ± 0.96 h) than the Lo NDF diet (4.54 ± 0.96 h). Although there was a difference in DM digestibility (Hi NDF: 50.1 ± 2.31%; Lo NDF: 60.0 ± 2.31%; P = 0.002), covariate analysis did not show a significant relationship between MRT or compartment parameters to diet digestibility. Additional research should pursue methods to ascribe physiological meaning to mathematically determined compartments. Nonetheless, the current data indicate using a multi-compartment model can identify differences in some digesta rate parameters between high and low fiber diets that were not apparent using total tract MRT alone.

影响饲料降解程度的一个因素是饲料在消化部位停留的时间长度。传统上，平均保留时间 (MRT) 是测量整个马胃肠道 (GIT) 的，但特定器官的保留时间可能与理解消化更相关。多隔间模型理论上将 GIT 分区以潜在地代表单个段中的 MRT。本研究的目的是将多隔室模型应用于饲喂以草料为基础的饮食的马的消化道通道。我们假设草料中性洗涤纤维浓度会改变总道 MRT、运输时间 (TT) 和隔间保留时间。六头阉马 (4 ± 1.5 岁, 545.0 ± 64.5 kg, 平均值 ± SD) 被随机分配一种蒂莫西立方体 (Hi NDF, n  = 3) 或苜蓿立方体 (Lo NDF,n  = 3) 以 1.53% BW 喂食并以 0.22% BW（干物质基础）浓缩。经过 15 天的饮食适应后，骟马会口服 Co-EDTA 和 Yb 标记的 NDF 残留物，以确定液体和颗粒物的保留时间。在标记物给药后 120 小时内进行总粪便收集。通过电感耦合等离子体光谱法分析样品的 Co 和 Yb 浓度。伽马分布的年龄相关的两个隔室模型适合每个阉割的标记排泄曲线（MATLAB，vR2014a）。通过方差分析 (SAS, v9.3) 分析饮食影响。饮食对全道 MRT 没有影响（液体 21.78 ± 0.79 小时，颗粒物 25.80 ± 0.79 小时，平均值 ± SEM）。然而，液体 TT 较长（P = 0.041) 在 Hi NDF 饮食 (7.25 ± 0.91 h) 中比在 Lo NDF 饮食 (3.86 ± 0.91 h) 中，并且 在 Hi NDF 饮食 (8.40 ± 0.84) 中液体年龄依赖性隔室保留时间更短 ( P = 0.019) h) 与 Lo NDF 饮食 (11.72 ± 0.84 h) 相比。 Hi NDF 饮食 (8.24 ± 0.96 h) 中的颗粒 TT比 Lo NDF 饮食 (4.54 ± 0.96 h)更长 ( P = 0.029)。尽管 DM 消化率存在差异（Hi NDF：50.1 ± 2.31%；Lo NDF：60.0 ± 2.31%；P = 0.002)，协变量分析没有显示 MRT 或隔间参数与日粮消化率之间的显着关系。额外的研究应该寻求将生理意义归因于数学确定的隔室的方法。尽管如此，目前的数据表明，使用多室模型可以识别高纤维和低纤维饮食之间某些食糜率参数的差异，而单独使用全道 MRT 则不明显。