The ideal protein profile for finishing pigs in precision feeding systems and phase feeding systems: threonine

Optimal amino acid (AA) ratios have been established for conventional group-phase-feeding systems (PP) but these ratios may differ for pigs fed individually with daily tailored diets (precision feeding systems, AIPF). The aim of this study was to compare the optimal threonine/lysine AA ratios between conventional PP and AIPF systems in finishing pigs. A hundred ten pigs (initial 110 kg BW (MSE= 7.02)) were arranged in a 2 x 5 factorial design with two feeding programs (AIPF or PP) and five threonine levels (TL) providing 70, 85, 100, 115 or 130% of recommended levels. Diets were formulated to provide 90% of the estimated lysine requirements while others AA (except threonine) were provided over 110% of requirements. Total body fat and lean content were estimated by Dual x-ray absorptiometry at the beginning (day 0) and at the end (day 21) of the trial. Blood samples were collected on day 21 at the jugular vein after 8-hour fasting. Plasma AA were analyzed by gas chromatography. Individual pigs were the experimental units. Means were analyzed by Tukey-Kramer multiple comparisons test using GLM procedure of SAS (version 9.3, Inst. Inc. Cary, NC, USA). Protein deposition was not affected by TL or feeding programs (P>0.05). Lysine and threonine intakes were 17% lower in AIPF than in PP (P<0.05) pigs. Fat deposition showed an interaction between feeding program and TL, with TL70 pigs in the AIPF and the TL85 in the PP having the greatest fat deposition. Plasma Lysine concentration was not affected (P>0.05) by feeding programs or TL. However, threonine concentration in plasma was different (P<0.05) between feeding programs and TL, with AIPF pigs having 5% lower concentration than pigs in the PP. AIPF pigs had 3% lower valine (P<0.05) and 6% higher glycine (P<0.05) plasma concentrations than PP pigs. Pig performance was not affected by threonine: lysine ratios. Nonetheless, AA plasma concentrations suggest that AA requirements may be different between group-phase-feeding and precision feeding systems.