Effect of lactose supplement on digestion of lucerne hay by sheep. II. Absorption of magnesium and calcium in the stomach.

Lactose (400 g/day) was added to a diet of lucerne hay (700 g/day chopped). The two diets (hay and hay plus lactose) were fed to four adult sheep fitted with rumen cannulas and simple cannulas at the proximal and distal end of the small intestine. The addition of lactose significantly increased apparent absorption of Mg, Ca and P and decreased slightly the apparent absorption of K. With lactose, absorption of Mg before the duodenum was significantly increased (41 vs 19%), and the increased Mg absorption from the stomach was associated with a net secretion of Mg into the small intestine. When hay was fed with lactose, more Ca was absorbed before the duodenum (30%) than when hay was fed alone (2%) and secretion of Ca into the small intestine was increased. Fermentation of lactose in the rumen induced decreases in pH and ammonia, a high lactate concentration and changes in molar proportions of volatile fatty acids. This work shows that readily fermentable carbohydrate increases stomach absorption of Ca and Mg and suggests that this effect is related to changes in fermentation patterns.