Replacement Value of Cystine for Methionine for the Young Pig

Summary

Two weight gain assays and one nitrogen retention assay were carried out to evaluate the replacement value of cystine for methionine in the diet of young pigs. An isolated soybean protein diet containing 12.2% protein was supplemented with graded decrements of methionine and graded increments of cystine to provide a total of 0.20% supplementary sulfur-bearing amino acids.

Under both group and individual ad libitum feeding conditions, weight gain was as rapid when 56% of the total sulfur amino acid requirement came from cystine, as when all was supplied by methionine. When equally fed in the nitrogen retention assay, the replacement value of cystine for methionine was 66%. Data from all three assays suggested that above a certain level of replacement (56%), cystine imbalances the diet, causing both reduced feed intake and gain. However, at equal levels of feed intake, maximal performance can be achieved on a diet containing at least 66% of the total sulfur amino acids as cystine.

© American Society of Animal Science 1969