Energy and SID lysine partitioning in pigs weighing 32–196 kg, voluntarily fed diets differing in SID lysine content

This study investigated the partitioning of metabolisable energy (ME) and standardised ileal digestible (SID) lysine in 96 Goland-C21 × Camborough-43 pigs, raised from 32 to 196 kg of body weight (BW) and fed voluntarily diets containing low (L), medium-low (ML), medium-high (MH), and high (H) SID lysine levels. Diets were formulated to provide decreasing SID lysine concentrations with increasing ages: early (90–118 d), late growing (119–146 d), and finishing (147–251 d). Individual feed intake was recorded using automated feeders, while BW and P2 backfat thickness were measured at the start and end of each interval to estimate protein (Pd) and lipid (Ld) deposition. Maintenance ME (MEm) was calculated by subtracting the energy required for Pd and Ld from total ME intake and scaled to BW0.60. Marginal SID lysine intake was determined as the difference between intake and maintenance requirements, based on the InraPorc model. The efficiency of SID lysine utilisation was calculated as the ratio of lysine deposited in Pd to marginal SID lysine intake. The L treatment provided insufficient SID lysine, resulting in lower final BW (p = 0.004), Pd (p = 0.003), and Ld (p = 0.023) compared to ML. However, ML, MH, and H treatments showed no significant differences. MEm averaged 0.961 MJ/kg0.60 BW, and lysine utilisation efficiency peaked at 0.68 in L pigs, aligning with InraPorc predictions. These findings support the applicability of the InraPorc model to pigs above 140 kg and offer updated SID lysine requirements across growth intervals.