Abstract Amino acid requirements are met in swine diets through a combination of synthetic amino acids (SAAs) and intact protein sources. Synthetic amino acids are provided in the diet in order to balance AAs that other ingredients are deficient in. Soybean meal (SBM) is a commonly used feedstuff utilized for its high AA and protein content. The objective of this experiment was to evaluate growth performance differences utilizing intact protein (SBM) vs. SAAs. A total of 96 mixed-sex pigs (13.9±0.15 kg) were used in a 28-d study. Pigs were placed in 24 pens to investigate the effects of intact protein (SBM) and SAAs on growth performance. Pens were stocked with 4 pigs per pen with approximately equal distribution of barrows and gilts. Dietary treatments were randomly allotted to pens within block by body weight (BW). Each dietary treatment was replicated 6 times. Treatments were arranged as a 2 × 2 factorial with SBM inclusion, low or high, and AA level, 80% or 100% of NRC (2012) requirements. Diets consisted of Low SBM 100% NRC, Low SBM 80% NRC, High SBM 100% NRC and High SBM 80%. No interactions were found between AA level and SBM level. The lmer function of R was used as a randomized complete block design with pen serving as the experimental unit, and the statistical model considered fixed effects of dietary treatment. Body weights (BW) were consistently higher after d 14 in the high SBM diets (P 0.05). From d 7-14, increasing SBM increased ADG and ADFI (P 0.01). G:F was also higher (P 0.01) in the high SBM diets. Additionally, during d 7-14, increasing SBM increased (P 0.01) ADFI. Overall (d 0-28), increasing SBM increased ADG and G:F (P ≤ 0.05). Increased ADG in the high SBM diets stayed consistent through the end of the trial (P 0.05). Utilizing 80% of the AA requirement in low and high SBM treatments decreased BW (P 0.01) and ADG (P 0.01). Overall (d 0-28), increasing SBM increased ADG and G:F (P 0.01) and tended to increase ADFI (P = 0.084). Overall data showed a tendency for decreased ADFI (P = 0.08) in low SBM diets along with decreased ADG (P 0.01) and increased G:F in high SBM diets (P 0.01). Increasing SBM inclusion improved BW, ADG and ADFI, suggesting growth performance benefits of high inclusion of SBM as prices decline. When decreasing AAs to 80% of NRC (2012) requirements, BW, ADG, ADFI and G:F were decreased. In conclusion, increasing SBM as an intact protein in diets at 100% NRC (2012) requirements improved growth performance. Greater inclusion of intact protein, such as SBM, may enhance energy utilization and protein synthesis for lean muscle tissue growth.
Pohlen et al. (Wed,) studied this question.