Seo S, Lanzas C, Tedeschi L O, Fox D G
Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2007 Feb;90(2):840-55. doi: 10.3168/jds.S0022-0302(07)71568-0.
A mechanistic and dynamic model was developed to represent the physiological aspects of liquid dynamics in the rumen and to quantitatively predict liquid flow out of the reticulorumen (RR). The model is composed of 2 inflows (water consumption and salivary secretion), one outflow (liquid flow through the reticulo-omasal orifice (ROO), and one in-and-out flow (liquid flux through the rumen wall). We assumed that liquid flow through the ROO was coordinated with the primary reticular contraction, which is characterized by its frequency, duration, and amplitude during eating, ruminating, and resting. A database was developed to predict each component of the model. A random coefficients model was used with studies as a random variable to identify significant variables. Parameters were estimated using the same procedure only if a random study effect was significant. The input variables for the model were dry matter intake, body weight, dietary dry matter, concentrate content in the diet, time spent eating, and time spent ruminating. Total water consumption (kg/d) was estimated as 4.893 x dry matter intake (kg/d), and 20% of the water consumed by drinking was assumed to bypass the RR. The salivary secretion rate was estimated to be 210 g/min during chewing. During ruminating, however, the salivation rate was assumed to be adjusted for the proportion of liquid in the rumen. Resting salivation was exponentially related to dry matter intake. Liquid efflux through the rumen wall was assumed to be the mean value in the database (4.6 kg/h). The liquid outflow rate (kg/h) was assumed to be a product of the frequency of the ROO opening, its duration per opening, and the amount of liquid passed per opening. Simulations of our model suggest that the ROO may open longer for each contraction cycle than had been previously reported (about 3 s) and that it is affected by dry matter intake, body weight, and total digesta in the rumen. When compared with 28 observations in 7 experiments, the model accounted for 40, 70, and 90% of the variation, with root mean square prediction errors of 9.25 kg, 1.84 kg/h, and 0.013 h(-1) for liquid content in the rumen, liquid outflow rate, and fractional rate of liquid passage, respectively. A sensitivity analysis showed that dry matter intake, followed by body weight and time spent eating, were the most important input variables for predicting the dynamics of liquid flow from the rumen. We conclude that this model can be used to understand the factors that affect the dynamics of liquid flow out of the rumen and to predict the fractional rate of liquid passage from the RR in dairy cattle.
建立了一个机理动态模型，以描述瘤胃内液体动力学的生理方面，并定量预测瘤网胃（RR）的液体流出量。该模型由2个流入量（水消耗和唾液分泌）、1个流出量（通过瘤网口（ROO）的液体流动）和1个进出流量（通过瘤胃壁的液体通量）组成。我们假设通过ROO的液体流动与原发性网状收缩协调，原发性网状收缩在进食、反刍和休息期间的特征在于其频率、持续时间和幅度。开发了一个数据库来预测模型的每个组成部分。使用随机系数模型，将研究作为随机变量来识别显著变量。仅当随机研究效应显著时，才使用相同程序估计参数。该模型的输入变量为干物质摄入量、体重、日粮干物质、日粮中的精料含量、进食时间和反刍时间。估计总水消耗量（kg/d）为4.893×干物质摄入量（kg/d），并假设20%的饮水绕过RR。咀嚼时唾液分泌速率估计为210 g/min。然而，在反刍期间，唾液分泌速率假设根据瘤胃中液体的比例进行调整。静息唾液分泌与干物质摄入量呈指数关系。假设通过瘤胃壁的液体流出量为数据库中的平均值（4.6 kg/h）。液体流出速率（kg/h）假设为ROO开口频率、每次开口持续时间以及每次开口通过的液体量的乘积。我们模型的模拟结果表明，每个收缩周期ROO的开放时间可能比先前报道的更长（约3 s），并且它受干物质摄入量、体重和瘤胃中总消化物的影响。与7个实验中的28个观测值相比，该模型分别解释了瘤胃液体含量、液体流出速率和液体通过分数率变化的40%、70%和90%，均方根预测误差分别为9.25 kg、1.84 kg/h和0.013 h⁻¹。敏感性分析表明，干物质摄入量，其次是体重和进食时间，是预测瘤胃液体流动动态的最重要输入变量。我们得出结论，该模型可用于了解影响瘤胃液体流出动态的因素，并预测奶牛瘤网胃的液体通过分数率。
