A new method for determining the availability of choline in soybean meal

Studies were conducted to evaluate the availability of choline in soybean meal, using a new approach: The basal diet contained soybean meal with a lowered choline content (partially extracted with methanol). Choline was added to the basal diet 1) by substituting intact soybean meal for the methanol washed soybean meal; or 2) from crystalline choline Cl. Four experiments were conducted with day-old male broilers housed in battery brooders and fed the experimental diets from 4 to 18 d posthatching. The basal diet contained corn, soybean meal, and isolated soy protein in Experiments 1 to 3, and also glucose in Experiment 4. In Experiment 1, chicks fed the basal diet (1,140 mg/kg choline, 0.61% sulfur amino acids) had a growth response to 1,000 mg/kg choline or 0.10% methionine (P < 0.05), but not to 0.10% cysteine (P > 0.05) supplementation. Supplementation of choline (0, 50, 100, 200, 400, 800, and 1,200 mg/kg) to the basal diet (1,230 mg/kg choline) in Experiment 2 resulted in a linear increase in growth up to 122 +/- 22 mg/kg supplemental choline (1,352 +/- 22 mg/kg total choline), reaching a plateau after that. In the slope ratio assays to determine choline availability, the basal diets in Experiments 3 (1,098 mg/kg choline) and 4 (920 mg/kg choline) were supplemented with either 50 or 100 mg/ kg choline (from choline Cl) or had approximately 50 or 100 mg/kg choline added with intact soybean meal (at the expense of washed soybean meal). There were significant linear responses of weight gain vs choline intake from either source (P < 0.001). The availability of choline in soybean meal was calculated to be 97 and 105% in Experiments 3 and 4, respectively. These results indicate that choline availability in soybean meal is close to 100%.