Growth performance of heavy pigs fed restrictively diets with decreasing crude protein and indispensable amino acids content

This study aimed to investigate the effect of decreasing dietary crude protein (CP) and indispensable amino acid (AA) content, relative to conventional diets, on growth performance of heavy pigs for dry cured ham production. Four dietary treatments (conventional: CONV, medium-high protein, medium-low protein, and low protein: LP) were formulated by replacing soybean meal with wheat grain to contain 146 to 117 and 133 to 108 g CP/kg in early (90 to 130 kg BW) and late finishing (130 to 165 kg BW) periods, respectively. Within period, diets contained the same amounts of indispensable AA per unit of CP, and the standardized ileal digestible (SID) Lys content was 42.2 and 35.5 g/kg of CP in early and late finishing periods, respectively. A total of 240 crossbred pigs, grouped in 3 batches of 80 pigs each, were assigned to one of 4 dietary treatments according to BWand sex (10 pigs per pen, gilts and barrows, and 2 pens per treatment in each batch). Pigs were fed restrictively using a single-space electronic feeder, and feed allowance increased from 2.4 at the start (92710 kg BW) to 3.2 kg/d at the end of the trial (167 kg BW), irrespective of sex. Initial and final BW and backfat depth (P2) measures were used to estimate body composition, and lipid and protein retention (Lr and Pr, respectively). These estimates, along with feed intake data, were used to study the partitioning of ME and SID Lys among body functions. Nitrogen excretion (NEx) was estimated as actual N intake – N retention, and N retention was computed as Pr/6.25. Final BW, average daily gain and final P2 backfat averaged 167 kg, 0.665 kg/d, and 18 mm, respectively. Diet had no effect on these traits, as well as on gain to feed ratio (0.253), Lr (265 g/d), Pr (95 g/d), and the ME available for maintenance (0.845 MJ/kg BW0.60). From CONV to LP the SID Lys intake decreased from 137 to 122 g/kg Pr, and NEx decreased by 22%. In this production system, a reduction of dietary CP and indispensable AA content is advisable, as no negative impact on growth performance was observed compared to CONV. A reduced inclusion of soybean meal with a minimal supplementation of AA reduces feed costs and NEx. This would increase the number of pigs raised per unit of land where a maximum N load/ha is constrained by law.