A total of 90 gilts were used to investigate the effects of various standard ileal digestible (
SID) total
sulfur amino acid (TSAA) to
lysine (Lys) ratios on the performance and carcass characteristics of late finishing gilts receiving low crude
protein (CP) diets supplemented with crystalline
amino acids (CAA). Graded levels of crystalline
methionine (Met) (0, 0.3, 0.5, 0.8 or 1.1 g/kg) were added to the basal diet to produce diets providing
SID TSAA to Lys ratios of 0.48, 0.53, 0.58, 0.63 or 0.68. At the termination of the experiment, 30 gilts (one pig per pen) with an average
body weight (BW) of 120 kg were killed to evaluate carcass traits. Increasing the
SID TSAA to Lys ratio increased average daily gain (ADG) (linear and quadratic effect, P < 0.05), improved feed conversion ratio (FCR) (linear and quadratic effect, P < 0.05) and decreased serum
urea nitrogen (SUN) concentration (linear and quadratic effect, P < 0.05) of finishing gilts. No effects were obtained for carcass traits. The optimum
SID TSAA to Lys ratios to maximize ADG as well as to minimize FCR and SUN levels were 0.57, 0.58 and 0.53 using a linear-break point model and 0.64, 0.62 and 0.61 using a quadratic model.