Effects of dietary SID lysine content on growth performance, feeding costs, and nitrogen excretion of growing and finishing pigs

This study evaluated the effects of different SID lysine levels on growth performance, feed costs, and nitrogen excretion of growing pigs raised for dry-cured ham production. Ninety-six Goland-C21 × Camborough-43 pigs (initial body weight, BW: 44.5 ± 3.8 kg) were allocated to four dietary treatments (2 pens/treatment, 12 pigs/pen) with low (L: 6.9, 6.0, 4.2 g/kg), medium-low (ML: 7.8, 6.9, 5.2 g/kg), medium-high (MH: 8.3, 7.8, 6.0 g/kg), or high (H: 9.3, 8.3, 6.9 g/kg) SID lysine across the growing (90–118 days), early finishing (119–132 days), and late finishing (133–233, days) phases. Automated feeding stations recorded individual feed intake. Backfat (BF) thickness and BW were measured at five time points. Nitrogen excretion was estimated from intake, retention, and atmospheric losses. Data were analysed using the PROC MIXED procedure in SAS; the model included dietary treatment, sex, and their interaction as fixed effects and pen nested within treatment as a random effect. Compared with L pigs, ML pigs showed similar feed intake and final BF depth but achieved higher (p < .05) final BW, greater average daily gain, and improved gain-to-feed ratio, while reducing feed costs (€1.63 vs €1.77 per kg BW gain) without increasing nitrogen excretion. Growth performance of ML pigs was comparable to that of MH and H pigs; however, ML diets resulted in the lowest feed costs and nitrogen excretion. These findings suggest that a medium-low SID lysine diet is sufficient for this pig population, effectively supporting growth performance while reducing feeding costs and environmental impact.