Xu C, Wensing T, Beynen A C
Department of Large Animal Medicine and Nutrition, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
J Dairy Sci. 1998 Aug;81(8):2173-7. doi: 10.3168/jds.S0022-0302(98)75795-9.
We tested the hypothesis that apparent digestibility of fat by veal calves is determined by the participation of bile acids in the process of fat absorption and is, therefore, negatively associated with bile acid excretion in feces. Veal calves were fed milk replacers that contained whey protein and either a low (5.2 g of calcium/kg of air-dried diet) or high (12.4 g of calcium/kg of air-dried diet) concentration of calcium. The high calcium milk replacer contained extra calcium in the form of calcium formate. Final body weight was not significantly influenced by diet after the milk replacers had been fed for 27 wk. Feces were quantitatively collected during wk 23 of the trial. The high calcium milk replacer reduced apparent fat digestibility by 5.6 percentage units and increased bile acid excretion in feces by 90% compared with the low calcium milk replacer. The extra calcium intake decreased apparent absorption of magnesium and phosphorus. We proposed that a high intake of calcium by veal calves would increase the amount of insoluble calcium, magnesium, and phosphate complexes in the intestinal lumen, which, because of the binding of bile acids, would exclude bile acids from the process of fat digestion and inhibit reabsorption of bile acids. As a result, fat digestion is impaired, and bile acid excretion in feces is enhanced. The complex formation in the ileal lumen also explains why high calcium intake reduces magnesium and phosphorus absorption in veal calves.
犊牛对脂肪的表观消化率取决于胆汁酸在脂肪吸收过程中的参与情况，因此与粪便中胆汁酸的排泄呈负相关。给犊牛饲喂代乳料，这些代乳料含有乳清蛋白以及低钙（5.2克钙/千克风干日粮）或高钙（12.4克钙/千克风干日粮）浓度的钙。高钙代乳料含有额外的甲酸钙形式的钙。在饲喂代乳料27周后，日粮对最终体重没有显著影响。在试验的第23周定量收集粪便。与低钙代乳料相比，高钙代乳料使表观脂肪消化率降低了5.6个百分点，并使粪便中胆汁酸排泄增加了90%。额外的钙摄入量降低了镁和磷的表观吸收率。我们推测，犊牛高钙摄入量会增加肠腔内不溶性钙、镁和磷酸盐复合物的量，由于胆汁酸的结合作用，这些复合物会将胆汁酸排除在脂肪消化过程之外，并抑制胆汁酸的重吸收。结果，脂肪消化受到损害，粪便中胆汁酸排泄增加。回肠腔内的复合物形成也解释了为什么高钙摄入量会降低犊牛对镁和磷的吸收。
