Uti Lization of Magnesium and Other Macrominerals in Sheep Supplemented with Different Readily- Fermentable Carbohydrates 1

Sheep were used to determine the effects of dietary supplementation with readily-fermentable carbohydrates on Mg, Ca, K and P utilization. In each of two metabolism trials, 15 mature, crossbred wethers (average weight, 49.2 kg) were allotted to five dietary treatments consisting of 800 g/d of orchardgrass (Dactylis glomerata, L.) hay alone, or supplemented with 450 g/d of either glucose, sucrose, lactose or starch. Each trial consisted of a 5-d adjustment period, a lo-d preliminary period and a lO-d collection period. Compared with wethers fed hay alone, supplementation with each kind of carbohydrate to the diet decreased (P<.05) fecal Mg excretion and increased (P<.05) apparent absorption and retention of Mg. Apparent absorption of the Ca was lower (P<.05) in wethers fed lactose and tended to be decreased by glucose, sucrose and starch supplementation. Calcium retention was lower (P<.05) in wethers fed sucrose and lactose, compared with those fed hay alone. All types of supplementary carbohydrates depressed (P<.05) apparent absorption and urinary excretion of K. Serum Mg and Ca were not affected and serum K was depressed (P<.05) by carbohydrate supplementation. Ruminal fluid pH was decreased (P<.05) by glucose and lactose supplementation, and addition of these carbohydrates tended to decrease molar proportions of acetate and increase those of propionate and butyrate, compared with sheep fed hay alone. Sucrose addition decreased (P<.05) acetate and increased (P<.05) butyrate molar proportions in the ruminal fluid. Ruminal NH3-N was lower (P<.05)in carbohydrate-supplemented wethers than in wethers fed hay alone. These results are interpreted to indicate that readily-fermentable carbohydrate supplementation improves availability of dietary Mg. (