Laying hens respond differently to high dietary levels of phosphorus in monobasic and dibasic calcium phosphate.

A series of experiments were conducted to determine the relative acidogenicities of dietary chloride, phosphorus, and sulfate and their effects on shell quality. Calcium salts of these anions were added to a corn-soybean meal diet to provide supplemental levels of 150 to 450 meq/kg diet chloride, 150 to 600 meq/kg diet monobasic phosphate, 150 to 1,200 meq/kg diet dibasic phosphate, and 150 to 1,200 meq/kg diet sulfate. The results indicated that laying hens can safely tolerate up to 200 meq/kg diet supplemental chloride (.95% total chloride in the diet) and up to 450 to 600 meq/kg diet supplemental sulfate (2.16 to 2.88% added sulfate). Levels higher than these adversely affected shell quality and altered blood acid-base balance. Laying hens responded quite differently to phosphorus when it was supplied as monobasic or dibasic phosphate. Supplemental levels of 900 to 1,200 meq/kg diet dibasic phosphate (1.95 to 2.41% total phosphorus) did not have an adverse effect on performance and up to a supplemental level of 450 meq/kg diet (1.25% total phosphorus) did not affect shell quality. In contrast, performance was seriously impaired by a supplemental level of 150 meq/kg diet monobasic phosphate (1.02% total phosphorus in the diet). The results further indicated that phosphate in monobasic (but not in dibasic) form is a strong acidogenic anion and that most of its adverse effect on performance and shell quality can be ameliorated by alkaline salts of sodium or potassium bicarbonate. The relative acidogenicities of calcium salts of these acidic anions were as follows: phosphate (monobasic) > chloride > sulfate > phosphate (dibasic).