Standardized amino acid digestibility in cecectomized roosters and lysine bioavailability in chicks fed distillers dried grains with solubles.

This study was conducted to compare the concentration of standardized digestible (SDD) Lys and relative bioavailable Lys in 7 sources of corn distillers dried grains with solubles (DDGS). A second objective was to evaluate 2 in vitro methods, reactive Lys and color score, to predict the concentration of SDD Lys and bioavailable Lys in DDGS. Seven sources of DDGS were fed to cecectomized roosters, and digestibility of amino acids was measured using the total excreta collection method. To measure the relative bioavailable Lys in DDGS, a standard curve (r(2) = 0.96, P < 0.01) was constructed from 9-d weight gain of young chicks fed a Lys-deficient basal diet or diets containing increasing concentrations of l-Lys-HCl. Seven additional diets were formulated by adding each of the 7 sources of DDGS to the basal diet, and total weight gain of chicks was measured. Weight gain of chicks fed each DDGS-containing diet was then compared with the standard curve to calculate the bioavailable Lys and bioavailability of Lys in each source of DDGS. All DDGS sources were analyzed for reactive Lys using the guanidination procedure, and a Hunterlab color score was used to measure the degree of lightness (L), redness (a), and yellowness (b). Results showed that the mean SDD Lys values and the mean relative bioavailability of Lys were 61.4 and 69.0%, respectively. Differences between the concentration of SDD Lys and the concentration of bio-available Lys were not observed in 5 of 7 sources of DDGS. The concentration of SDD Lys was correlated (r(2) = 0.84, P < 0.05) with the concentration of reactive Lys in DDGS. Greater Hunterlab L scores were associated with a greater (r(2) = 0.90, P < 0.05) concentration of bioavailable Lys in DDGS. In conclusion, the concentration of SDD Lys in DDGS does not overestimate the concentration of bioavailable Lys for poultry. Values for reactive Lys may be used to estimate the concentration of SDD Lys, whereas Hunterlab L may be used to estimate the concentration of bioavailable Lys in DDGS.

Excess dietary methionine markedly increases the vitamin B-6 requirement of young chicks.

A soy-protein isolate diet that contained essentially no bioavailable vitamin B-6 was used to establish the quantitative effect of excess dietary methionine on the vitamin B-6 requirement of young chicks. When made adequate in vitamin B-6, chicks fed the basal diet required 2 g/kg supplemental DL-methionine to achieve maximal growth, and 10 g/kg additional DL-methionine (total = 12 g/kg) was found to be a tolerable excess level that would not depress voluntary food intake or growth rate. When chicks were fed seven graded doses of supplemental pyridoxine (PN) in diets that contained either adequate (2 g/kg) or excess (12 g/kg) methionine, the vitamin B-6 requirement for maximal growth was found to increase (P: < 0.01) from 0.73 to 1.05 mg/kg, a 44% increase, when 10 g/kg excess methionine was present in the diet. Indeed, this level of excess dietary methionine depressed (P: < 0.01) growth at all PN dose levels < or =1 mg/kg, but not at PN doses of 1.2 or 1.4 mg/kg. Because dietary intakes of both vitamin B-6 and methionine can affect plasma homocysteine levels, dietary methionine (and protein) intake should be considered important factors in setting safe and adequate requirement levels for vitamin B-6.