A model was developed in growing piglets to study the use of urinary total sulfur excretion as an indicator of sulfur amino acid (SAA) catabolism and the nitrogen (N)/sulfur (S) balance ratio as an indicator of non-protein SAA storage. The recovery of administrated methionine as urinary total S over 48 hours was 106% in well-nourished piglets, but only 69% in protein malnourished piglets. The N/S balance ratio of protein malnourished piglets was lower than that of well-nourished piglets, and this ratio further decreased after methionine administration. We conclude that in a protein malnourished state, relatively more S than N is retained and a significant portion of the S derived from administrated methionine is retained in non-protein pools. These results demonstrate that urinary total S excretion can provide an accurate measure of SAA catabolism; and the N/S balance ratio can provide valuable information about non-protein SAA storage in growing piglets.

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