The Ideal Dietary Protein Profile for Finishing Pigs in Precision Feeding Systems and Phase Feeding Systems: Threonine

Optimal AA ratios have been established for conventional group phase feeding (GPF) systems, but these ratios may differ in finishing pigs when fed with precision feeding systems (IPF). The aim of this study was to evaluate the response of different levels of threonine (Thr; 70, 85, 100, 115 and 130% of the 0.65 Thr: Lysine ideal protein ratio) in pigs raised in GPF or IPF systems. A 110 finishing pigs (110 kg BW ± 7.02; 11 pigs per treatment) were housed in the same pen and fed for 21 days using automatic feeders. Individual pigs were the experimental units. Five pigs per treatment were slaughtered at the end of the trial. Data were analyzed in a 2x5 factorial arrangement by the mixed model procedure of SAS . During this finishing phase, G: F presented a quadratic effect for Thr levels (P<0.05) and was not affected by feeding programs. The intake of SID Lys and Thr were greater (P<0.05) in GPF (Lys: 24 g/d; Thr: 18 g/d) than IPF (20 g/d; Thr: 15 g/d) pigs. Protein deposition (PD) was higher in GPF (130 g/d) than IPF pigs (122 g/d; P<0.05), while the level×feeding system interaction for protein in gain presented a quadratic effect of Thr level for GPF (average minimum: 10.7%, maximum: 12.4%; P<0.05) and a no effect of Thr level for IPF (average minimum: 10.3%, maximum: 11.7%; P<0.10). Pigs in IPF systems consumed 14% less crude protein and excreted 17% less nitrogen than GPF pigs (P<0.05). Pigs in IPF retained 9% more nitrogen than GPF pigs (P<0.05) and the Thr level effect was quadratic in both systems (P<0.05). Threonine concentration in plasma presented a linear increase (P<0.05) as Thr in the diet increased and Thr in plasma was 8% higher in the plasma for GPF (203 µmole/L) pigs than IPF pigs (187 µmole/L). Dietary Thr levels had a cubic effect on arginine and histidine, as well, quadratic effect on valine in the liver of pigs in both systems (P<0.05). Pigs in IPF had a different response to Thr levels than pigs in GPF system, the last had higher PD at Thr: Lys ratio of 0.85 while in IPF Thr: Lys ratio had no impact on PD.