Abstract A 56-day study was conducted to evaluate the effect of guanidinoacetic acid (GAA) or ractopamine (RAC) supplementation on growth performance and body composition of finishing pigs. Thirty-three immunocastrated male pigs with initial body weight (BW) of 76.5 ± 5.6 kg were randomly assigned to one of two dietary treatments. A basal diet (BD), based on corn, wheat bran and soybean meal was produced for 75 to 100 kg pigs Phase 1; 0.81% standardized ileal digestible (SID) Lys, 10.14 MJ/kg NE and for 100 to 125 kg BW (Phase 2; 0.78% SID Lys, 10.01 MJ/kg NE). The SID Lys was 11% and 24% above the NRC (2012) recommendation for Phase 1 and 2, respectively. Treatments were: 1) BD from day 0 to 28 and BD + Ractopamine HCl (10 g/t) from day 29 to 56 (RAC; n = 17), and 2) BD + GAA (900 g/t) from day 0 to 56 (GAA; n = 16). Pigs had free access to pellet feed and water. Feed intake was measured using automatic feeders, and pigs were individually weighed at the beginning and end of each phase. Body fat and lean contents were assessed by dual-energy X-ray absorptiometry. Blood samples (10 pigs/treatment) were collected on days 0, 28 and 56 to measure plasma concentrations of metabolites. Data were analyzed using GLIMMIX procedure in SAS with dietary treatments as fixed effects and replicate as a random effect. Final BW (day 56) of pigs fed GAA tended to be greater (142.5 vs. 137.1 kg; P = 0.082) compared with RAC group. Compared with RAC, GAA supplementation increased (P 0.05) ADFI in phase 1 (2.32 vs. 2.53 kg), phase 2 (3.34 vs. 3.67 kg), and the overall period (2.86 vs. 3.17 kg). ADG was higher (P 0.05) for GAA pigs compared with RAC group during phase 1 (1.07 vs. 0.97 kg), and the overall period (1.22 vs. 1.12 kg), however, GAA did not affect (P 0.05) G:F in all phases. Body protein contents of pigs fed GAA or RAC at day 28 and 56 were not different (P 0.05). Body lipid contents of pigs fed GAA was not different at day 28 (P 0.05) but tended to be higher at day 56 (24.3 vs. 21.9 kg; P = 0.088) compared with RAC. Plasma concentrations of all metabolites were not different at day 28 (end of phase 1), however, pigs fed GAA tended to have a lower plasma lactate (P = 0.085) and lower protein level (P = 0.027) at day 56 compared with RAC. These results indicate that GAA supplementation in finishing pig diet increases ADFI and ADG and may improve energy (glucose) metabolism by preventing excess lactate in plasma.
Htoo et al. (Wed,) studied this question.