Development of an experimental diet for determining bioavailable choline concentration and its application in studies with soybean lecithin.

Attempts to determine choline bioavailability have encountered criticism of experimental diets and protocol. Our objectives were to develop a choline-deficient soy isolate diet to quantify bioavailable choline concentration of soybean lecithin and to compare results to those obtained with a purified diet. In Assay 1, weight gain of chicks fed a choline-free crystalline amino acid diet responded linearly (P < .01) to graded doses of choline chloride, fluid lecithin (FL), or deoiled lecithin (DL). Multiple linear regression analysis indicated a bioavailable choline content of 2.3 and 3.7% for FL and DL, respectively. In Assay 2, a choline-deficient soy isolate diet was supplemented with 2-amino-2-methyl-1-propanol (AMP) to inhibit choline biosynthesis. Weight gain, feed intake, and feed efficiency increased (P < .05) markedly with the addition of choline chloride, but supplemental methionine or betaine had no effect (P > .10). Addition of 10% soybean meal to the diet severely deficient in choline per se produced a growth response (P < .05), whereas the same addition to the diet made adequate in choline did not elicit a growth response. In Assay 3, addition of graded levels of choline chloride, FL, or DL to the choline-deficient soy isolate diet containing AMP resulted in a linear (P < .01) increase in weight gain and feed intake. Multiple linear regression analysis indicated a bioavailable choline content of 2.0 and 3.5% for FL and DL, respectively. The AMP-containing soy isolate diet seems well suited for determination of bioavailable choline content in products containing secondary nutrients. Bioavailable choline content of FL and DL was similar to estimates of total choline content, suggesting that the choline in these products was fully available.