Gompertz growth curves and energy and protein requirements of heavy pigs raised under non-restricted and restricted growing conditions

Data from our previous experiment were used to model the chemical growth of 323 pigs raised under non-limiting environmental and feeding conditions. The study assessed the pigs' metabolizable energy (ME) and standardized ileal digestible (SID) lysine requirements. In addition, the effects of restricting feed and SID lysine intake on growth and nutrient requirements were examined. The pigs arrived at the testing facility weighing 89 ± 12 kg at 142 ± 3 d of age. One group was fed high-protein diets ad libitum until 8 to 9 months old, while the other two groups were fed medium or low-protein diets, restricted by approximately 20%, until they reached 170 kg at 9 months or older. Live weight and backfat depth were measured repeatedly to estimate individual empty body weight, body protein, and lipid masses at various ages. The data were fitted using the Gompertz growth model, and ME and SID lysine requirements were estimated for pigs older than 150 d, based on literature. The average mature protein mass of the ad libitum-fed pigs was 38.7 kg, with a maximum potential protein gain of 183 g/day at 140 d of age. The mature lipid mass was 115 kg, with a maximum potential lipid gain of 385 g/day at 216 d, and a lipid-to-protein ratio of 2.96 at maturity. Based on our findings, for pigs with a similar genetic background raised for dry-cured ham production, we recommend reducing dietary SID lysine levels from 7.33 to 3.23 g/kg as age increases from 150 to 270 d, assuming a feed intake of 2.91–3.30 kg/day. Both feed and protein restrictions exerted significant impacts, with all growth parameters consistently diminishing in proportion to the level of imposed dietary nutrient restriction. The recommended dietary SID lysine levels for pigs subjected to dietary nutrient restriction feed-restricted pigs were similar to those found in ad libitum-fed pigs, and both were significantly lower than the industry standards typically used in feed formulations.