A Laboratory Technique for Measuring Phosphorus Availability of Feed Supplements Fed to Ruminants

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Abstract
An in vitro fermentation with rumen microorganisms (artificial rumen) was developed to measure phosphorus availability of cattle and sheep feed supplements. Cellulose digestion in a series of fermentation tubes was related to graded amounts of phosphorus added at the beginning of a 24-hour fermentation period. A preliminary fermentation making use of a washed suspension of rumen microorganisms in a phosphorus-deficient medium greatly facilitated the assay fermentation. Also the use of specially hydrolyzed casein or feather meal added to the medium proved helpful in obtaining the greatest response of phosphorus additions upon cellulose digestion. Among the supplements assayed it was found that composite dicalcium phosphate appeared to be as available as a standard sodium-potassium phosphate mixture. An acidulated phosphorus product and steamed bone meal were intermediate in phosphorus availability while Curacao rock phosphate and colloidal clay appeared to be less available. The merits of this laboratory technique in measuring phosphorus availability were discussed with respect to their transposition to feeding practice in cattle and sheep.

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