Effects of intrinsic potassium in artificially dried grass and supplemental potassium biocarbonate on apparent magnesium absorption in dry cows
1999
Schonewille, J.T. | Klooster, A.T. van't | Wouterse, H. | Beynen, A.C.
Literature data indicate that the form of K in the ration can affect its inhibitory influence on Mg absorption in ruminants. We tested whether identical amounts of K either intrinsically present in artificially dried grass or present in added KHCO(3) have different effects on Mg absorption in dry cows. In a 3 x 3 Latin square design, six cows were fed rations consisting of low-K grass and concentrate with or without KHCO(3) or a ration consisting of high-K grass with concentrate without added KHCO(3). Each ration was given for a period of 4 wk. The ration low in intrinsic K contained 26 g of K/kg of dry matter, the ration low in intrinsic K plus KHCO(3) contained 43 g of K/kg of dry matter, and the ration high in intrinsic K also contained 43 g of K/kg of dry matter. The three rations were balanced for crude protein, crude fat, crude fiber, Mg (2.2 g/kg of dry matter), Ca, P, and Na. Apparent Mg absorption was 10.8 +/- 1.54% of intake (mean +/- SE, n = 6) when the cows were fed the low-K ration, but dropped to 1.9 +/- 3.4 and 2.1 +/- 1.9% of intake, respectively, when the rations high in KHCO(3) and high in intrinsic K were fed. The two high-K rations induced similar increases in ruminal K concentrations both before and after feed consumption. The feeding of KHCO(3) did not influence ruminal pH. The intake of extra K may raise ruminal K concentrations, which increases the transmural potential difference so that Mg transport across the rumen epithelium becomes depressed. Thus, intrinsic and added K had identical effects on ruminal K concentrations and on Mg absorption. Feeding trials with ruminants in which K intakes are manipulated with the use of KHCO(3) may reflect those cases when concentrations of K intrinsically present in feedstuffs may vary.
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