Effects of potassium on macromineral absorption in sheep fed wheat straw-based diets.

Two experiments were conducted to determine the effect of increasing dietary K on macromineral bioavailability from a wheat straw-hay diet, and to monitor changes in the rumen that could affect mineral availability. In the first experiment, 12 mature wethers were used in a metabolism study to determine the effect of adding potassium chloride (KCI) to a supplement fed with a diet of 55% NH3-treated wheat straw and 45% bromegrass hay. In the second experiment, similar diets were fed to six wethers with ruminal and abomasal cannulae to determine the site of mineral absorption. Dietary K levels were 1, 2 and 3% of the diet dry matter. Increasing K tended to decrease (P<.06) apparent absorption of Mg. Potassium absorption increased (P<.01) with increasing dietary K, but retention was not altered. Quadratic effects (P<.01) of K were observed for Ca and P apparent absorption and retention. Increased K lowered (P<.05) plasma Mg in Exp. 1 but not in Exp. 2. Ruminal concentrations of K increased (P<.01), and concentrations of Na decreased (P<.05), as dietary K increased. Ruminal fermentation was influenced by dietary K level. Molar proportions of acetate in the rumen were increased (P<.01) by the addition of K to the diet, while molar proportions of butyrate (P<.01) and valerate (P<.01) decreased linearly with increasing K. Time X treatment interactions were present for mminal propionate, buryrate and NHfN (P<.01). Data are interpreted to suggest that Mg bioavailability was lowered by addition of KCI to the diet. This decrease may have been caused by changes in ruminal mineral concentrations or fermentation patterns.