This study aimed to determine the requirements of standardized ileal digestible (SID) methionine (Met) + cysteine (Cys) of 15–30 kg barrows, maintaining or increasing the 1:1 ratio between SID Met and SID Cys. Seventy crossbred barrows averaging 15.2 ± 0.54 kg of live weight were allotted in a randomized block design 2 × 3 + 1 factorial scheme, with five replicates and two animals per pen. Treatments consisted of maintaining or increasing the 1:1 ratio between SID Met and SID Cys, three levels of SID Met + Cys (5.8, 6.4 and 7.0 g/kg) and a basal diet containing the lowest SID Met + Cys level (5.2 g/kg), formulated to provide a 1:1 ratio of SID Met (2.6 g/kg) and SID Cys (2.6 g/kg). Performance, blood parameters, longissimus dorsi muscle depth, backfat thickness and S–S linkages in the bristles were evaluated. The best average daily gain was estimated at 6.61 g/kg of SID Met + Cys, without maintaining the 1:1 ratio between sulphur amino acids (SAA). The daily intake of SID Met + Cys increased due to dietary SID Met + Cys levels, maintaining or increasing the same ratio between SAA. Plasma glucose increased and total cholesterol decreased according to SID Met + Cys levels, without maintaining the same ratio between the SAA. The requirement of SID Met + Cys for 15–30 kg barrows was 6.61 g/kg (7.88 g/day) for an optimum average daily gain, with no need to maintain the same ratio between the SAA.

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