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Effect of Potassium on Association of Minerals with Various Fractions of Digesta and Feces of Sheep Fed Hay^1,2,

Virginia Polytechnic Institute and State University³, Blacksburg 24061

Abstract

An experiment was conducted with 12 crossbred (Finn x Dorset x Suffolk) wethers (42 kg), fitted with ruminal, abomasal and ileal cannulae to study the effect of K administration on the association of Mg, Ca, K and Na with various fractions in digesta and feces. The wether were fed 800 g of orchardgrass hay and dosed with 2 g Cr₂O₃, as solid marker and 2 g cobalt ethylene-diaminetetraacetate (EDTA), as liquid marker, daily. Six wethers were used as controls and the other six were dosed with 100 g KHCO₃/head daily, via the ruminal cannulae at the time of feeding. Feed, feces and digesta samples were treated with tris buffer and separated into liquid and solid fractions. The liquid fraction was treated with ethanol and separated into liquid and ethanol precipitated parts. The solid fraction was extracted with chloroform:methanol. The residue from this extraction was further treated with LiOH-EDTA and centrifuged into liquid and solid entities. Administration of KHCO₃ resulted in an increase in ruminal pH with no effect on abomasal, ileal and fecal pH. Urinary excretion of Mg was decreased (P<.05) and that of K was increased by KHCO₃ administration. Most of the Mg in the diet and feces was associated with the solid fraction (75%) and, in the abomasum, with the liquid fraction (74%). Magnesium in the rumen and ileum was divided approximately equally between the solid and liquid fractions. All the Mg and 50 to 70% of the Ca present in the liquid fraction in the rumen were associated with protein. None of the Mg or Ca in the abomasum was precipitated with ethanol. Administration of KHCO₃ had no effect on Mg solubility, but it resulted in an increase (P<.05) in ruminal solubility of Ca. It is concluded that solubilities of Mg and Ca in the digesta may not be indicators of their availability for absorption. Also it is possible that the effect of increasing K above 3.2% on Mg absorption may be limited.

¹ Supported by John Lee Pratt Anim. Nutr. Program.

² Sincere appreciation is extended to Mrs. V. Bowman for her assistance in laboratory analysis.

³ Dept. of Anim. Sci.