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Experiments were conducted to determine the effects of supplementing corn-soy-bean meal-white grease diets with sulfur amino acids and methyl group donors for starting broiler-strain chicks. The diets (23% protein and 3200 kcal ME/kg) were fed to quadruplicate lots of chicks in battery brooders. The diets were calculated to contain .37% methionine, .37% cystine, and 1499 mg/kg choline. Chemical and microbiological assays yielded values of .32% and .42% for methionine and cystine content respectively. Results of 5 chick experiments showed that supplementing this diet with .23% DL-methionine significantly (P less than .05) improved 3 week-gain (375 vs. 415 g) and feed/gain (1.54 vs. 1.47) over that obtained with the basal diet. When L-cystine and 2(CaSO4).H2O failed to give a significant (P greater than .05) response, compounds capable of donating methyl groups were fed. Significant (P less than .05) responses in gain (404 and 420) and feed/gain (1.48 and 1.51) over the basal were obtained with choline and betaine. These responses were not significantly (P greater than .05) different from that obtained with methionine. Serine and sodium formate failed to give consistent responses. Using a poult diet of 28% protein and 2800 kcal ME/kg, a significant (P less than .05) response to DL-methionine was again observed, with intermediate responses to betaine, choline, and serine. It is concluded that (within the limits of the experimental model) corn-soy type diets contain an adequate amount of total sulfur amino acid for chicks, but not poults, when sufficient choline or betaine are provided.

Experiments were conducted to test the hypothesis that metabolically labile methyl groups and not methionine per se are limiting the growth of starting broiler chicks fed corn-soy-grease diets formulated to meet NRC (1977) recommendations (except for methionine). The basal diet contained approximately 23% protein, 3200 kcal ME/kg. 32% methionine, .42% cystine, and 1300 ppm choline. In the first two experiments the diets were fed to quadruplicate lots of 10 chicks in battery brooders. Average weight gain (g) and feed per unit gain for supplements of methyl group sources were: 1) methionine: 424, 1.48; 2) choline Cl: 406, 1.49; and 3) betaine HCl: 416, 1.48. These values were not significantly different from one another (P greater than .05) but were significantly different (P less than .05) from the values for the basal (362, 1.57) and from the DL-homocystine supplemented groups (376, 1.56). This indicated that methyl group utilization was not impaired by a lack of the carbon skeleton of methionine. Five 3-week assays with five groups of 10 chicks per treatment (1050 chicks) were conducted to determine the choline requirement using the basal diet without supplemental methionine. Results from the five assays were pooled in computing regressions. Significant regressions (P less than .05) were found for broken-line linear (R2 = .630), quadratic (R2 = .556), and saturation kinetic (R2 = .642) models. The requirement was determined to approximately 2130 ppm by the broken-line linear model. The most economic feeding levels were estimated to be 4100 and 1910 ppm by the quadratic and saturation kinetic models, respectively. The economic implications of the three models are discussed.