Maintaining the same ratio between standardized ileal digestible methionine and cysteine do not affect its requirements for starting pigs

Abstract

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.