The Effect of Methionine and Cystine on the Growth of Weanling Pigs

When purified diets containing oxidized casein, gelatin and tryptophan to make a total of 21.0% protein in the ration were fed ad libitum, a methionine deficiency was observed in weanling Duroc pigs. The level of methionine which supported the best rate of gain and feed efficiency was 0.6% of the diet when 0.01% cystine was present in the ration.If adequate cystine was present in the ration, 0.3% methionine supported a rate of gain and feed efficiency which was equivalent to that obtained when 0.6% methionine plus 0.6% cystine were fed. Tentatively, the methionine requirement for weanling pigs is set at 0.6% of the ration in the absence and 0.3% methionine in the presence of adequate (0.3% or more) cystine.