title: Effects of intrinsic potassium in artificially dried grass and supplemental potassium bicarbonate on apparent magnesium absorption in dry cows.
abstract: 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 KHCO3 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 KHCO3 or a ration consisting of high-K grass with concentrate without added KHCO3. 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 KHCO3 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 KHCO3 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 KHCO3 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 KHCO3 may reflect those cases when concentrations of K intrinsically present in feedstuffs may vary.
authors.affiliation: Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
authors.forename: J T
authors.initials: JT
authors.lastname: Schonewille
authors.forename: A T
authors.initials: AT
authors.lastname: Van't Klooster
authors.forename: H
authors.initials: H
authors.lastname: Wouterse
authors.forename: A C
authors.initials: AC
authors.lastname: Beynen
mesh_terms: D000042:Absorption; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D004435:Eating; D005260:Female; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000097:blood / Q000378:metabolism*; D006109:Poaceae / Q000737:chemistry*; D011188:Potassium / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D017680:Potassium Compounds / Q000494:pharmacology*; D012417:Rumen / Q000033:anatomy & histology / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D017680:Potassium Compounds; C026329:potassium bicarbonate; D008274:Magnesium; D011188:Potassium