Quiroz R A, Pond K R, Tolley E A, Johnson W L
North Carolina State University, Raleigh 27695.
J Anim Sci. 1988 Nov;66(11):2977-86. doi: 10.2527/jas1988.66112977x.
Eight Toggenburg wether goats were fed either Coastal bermudagrass (Cynodon dactylon) or orchardgrass (Dactylis glomerata)-alfalfa (Medicago sativa) hay (57:43%) in a reversal design. Four markers were used to study the movement of different digesta fractions: erbium for large particles greater than 1,700 microns; ytterbium for medium particles less than 1,700 microns and greater than 500 microns; chromium for small particles less than 500 microns and greater than 32 microns; and cobalt to follow liquid passage. Fecal samples were collected every 4 h for 6 d. The excretion curves obtained for every marker in each animal were used for model selection. One-compartment gamma age-dependent models (gamma 2, 3 and 4 age-dependent), two-compartment (gamma 2 and gamma 3 age-dependent, age-independent) models and a biexponential model were fitted to the data. Residual sums of squares and the Davidson and MacKinnon test were used to select the most appropriate models. These procedures indicated that the models best describing the movement of different digesta fractions through the gastrointestinal tract of goats, in this experiment, were the biexponential model for liquids, gamma 2 two-compartment model for small and medium particles and gamma 3 two-compartment model for large particles. To accurately describe the behavior of different components of digesta in the digestive tract, different mathematical models are required. In general, models that describe the movement of large particles have higher orders of age-dependency than models that describe the passage of liquids or small particles.
八只托根堡阉公羊采用交叉设计，分别饲喂海岸百慕大草（狗牙根）或果园草（鸭茅）-苜蓿（紫花苜蓿）干草（比例为57:43%）。使用四种标记物来研究不同消化物组分的移动情况：铒用于标记大于1700微米的大颗粒；镱用于标记小于1700微米且大于500微米的中颗粒；铬用于标记小于500微米且大于32微米的小颗粒；钴用于追踪液体的通过情况。连续6天，每4小时采集一次粪便样本。利用每只动物每种标记物的排泄曲线进行模型选择。将单室γ年龄依赖性模型（γ 2、3和4年龄依赖性）、双室模型（γ 2和γ 3年龄依赖性、年龄独立性）和双指数模型拟合到数据中。使用残差平方和以及戴维森和麦金农检验来选择最合适的模型。这些程序表明，在本实验中，最能描述不同消化物组分在山羊胃肠道中移动情况的模型是：液体的双指数模型、中小颗粒的γ 2双室模型和大颗粒的γ 3双室模型。为了准确描述消化道中消化物不同成分的行为，需要不同的数学模型。一般来说，描述大颗粒移动的模型比描述液体或小颗粒通过情况的模型具有更高阶的年龄依赖性。
