Pigs Receiving Daily Tailored Diets Have Different Amino Acid Requirements Than Pigs Raised in Conventional Phase Feeding Systems

There is a large variation in nutrient requirements among pigs and therefore, feeding pigs individually with daily tailored diets may require different nutrient levels than when pigs are feed in groups with a single feed. Thus, the response to different levels of Thr: Lys ratio (70, 85, 100, 115 and 130% of the 0.65 Thr: Lys ideal ratio) was studied in growing pigs raised in conventional group feeding (GF) systems or individually fed using precision feeding (PF) techniques. A 21 days trial was performed in a 2×5 factorial design with 110 pigs (25 kg BW ± 0.80, 11 pigs per treatment) housed in the same pen and fed using electronic feeders. Individual pigs were the experimental units. Lysine was provided at 90%, and other AA than Lys and Thr at 110% or more, of the estimated requirements. Protein deposition (PD) was estimated using Dual X-ray absorptiometry at the d 1 and d 21. Blood samples were collected on d 21 after 8 h fasting, and five pigs per treatment were slaughtered. The chemical composition of the longissimus dorsi and other carcass muscles were estimated by near-infrared transmittance. The Mixed and NLIN procedures of SAS were used to analyze the data and obtain optimal Thr: Lys ratios. Threonine intake increased linearly in PF and GF (6.28 to 11.76 vs. 6.85 to 11.01 g/d, P < 0.05). Lysine intake was similar (12.5 g/d) across treatments. The intersection of the linear-plateau and quadratic-plateau models for PD was obtained in GF pigs at 150 g/d and 0.65 Thr: Lys ratio whereas maximal PD was not reached in PF pigs (126 to 159 g/d). Plasma methionine and serine levels were respectively, 11% and 7% higher in PF than in GF pigs (P < 0.05). Carcass muscle CP was 2% higher in GF (18.1 %) than in PF pigs (17.8 %, P < 0.05). Longissimus dorsi collagen tended to decrease with increasing dietary Thr in PF and GF (0.61 to 0.45% vs. 0.55 to 0.54%, P < 0.10). Plasma albumin increased with the level of Thr in PF and GF (29.1 to 34.9 vs. 30.8 to 32.5 g/L, P < 0.05) indicating a possible defective albumin synthesis at lower Thr levels. Altogether, the Thr: Lys ratio that maximizes growing pig responses differ between conventional and precision feeding systems and therefore, actual Thr: Lys ideal ratios may not be optimal for pigs fed with daily tailored diets.