Recent findings on the net energy of soybean meal

The use of feed-grade amino acids (FGAA) is an important tool to lower feed cost while lowering nitrogen emission for swine and poultry producers. When FGAA’s are used within the known limits, they can improve animal performance and enhance carcass value. However, when lowering dietary crude protein via soybean meal (SBM) or other protein sources, care must be taken as all the EAA ratios to SID Lys are not well established especially for 7th, 8th limiting amino acids and minimum nitrogen requirements for non-essential amino acid de novo synthesis.

The net energy (NE) of soybean meal (SBM) has been an intense topic of debate in the US swine nutrition community. Recent published works (Cemin, et al., 2020, Holden, et al., 2022) suggested the net energy of SBM is much higher than NRC (2012) estimates. In fact, Cemin et al., (2020) has suggested it is higher than corn. A total of 2,153 finishing pigs (PIC 337 × 1050; initially 28.8 ± .47 kg) were used in a 112-d growth study to determine the NE of SBM relative to corn and feed-grade amino acids (FGAA). The four treatments consisted of a diet containing a low level of SBM and added FGAA (Low SBM) and three diets with a 3.37 (Med-Low SBM), 6.69 (Med-High SBM), and 10% (High SBM) increase in SBM compared to the Low SBM diet with FGAA. The High SBM diet did not contain any feed-grade L-lysine-HCl. Treatment diets were fed in four dietary phases. Increasing dietary levels of FGAA with corresponding decreasing levels of dietary SBM resulted in linear (P<.01) increase in ADG resulting linear (P<.01) heavier body weight (BW) at day 56 and 112. ADFI was linearly increased (P<0.001) from day 0 to 56 and over the trial period (P<.004) with increasing levels of FGAA. FCR was unaffected (P>.10) from day 0 to 56, but linearly (P<.03) improved with increasing levels of FGAA from day 56 to 112 but was unaffected (P>.10) over the entire 112-day trial. Increasing dietary level of SBM resulted in a linear (P<.03) increase in mortality percentage and total mortalities plus removal percentage. Carcass weight, yield percentage and carcass ADG linearly (P<.001) increased with increasing FGAA and decreasing dietary SBM levels. Increasing dietary FGAA increased back fat (BF) (P<.05) and carcass lean percentage in a quadratic manner. SBM NE value relative to corn was estimated using adjusted dietary caloric efficiency at 93.5% on a liveweight basis or 83.9% on a carcass weight basis relative to corn. In this study, the NE of SBM was higher than the NRC 2012 values but was not equal to or higher than that of corn.

BACKGROUND
The NRC (2012) added NE estimates in addition to traditional digestible energy (DE) and metabolizable energy (ME) estimates in their 2012 ingredient matrix tables. In visiting with members of NRC’s committee, they elected to use the Noblet NE equations (Noblet and van Milgen, 2004) over other systems. Thus, the calculated NRC (2012) NE of SBM relative to corn is stated at 78% (2,087 kcal/kg). With additional FGAA becoming economically feasible for use in swine and poultry diets, considerable work on using these newer FGAA (L-valine (Val), L-isoleucine (Ile) and L-Arginine (Arg) has been completed. A recent trial was conducted by Cemin et al. (2020) evaluated varying levels of SBM from very low to high diets supplemented with FGAA to meet NRC (2012) recommendations. The authors used NRC (2012) NE estimates to calculate total dietary NE and then calculate caloric efficiency (CE, calculated by multiplying total feed intake × energy content of the diet (kcal/kg) and dividing by total gain). In evaluating all their data points, they estimated the NE of SBM at 105% of corn and 120% or higher using different methods.

In reviewing the trials suggesting NE value of SBM is higher that provided by corn, we have concerns with the trial designs. Authors balanced AA ratios to lysine down to histidine, but did not account for phenylalanine, tyrosine nor arginine in their formulation. Additionally, they conclude all the change in CE is due to NE of SBM alone, which is doubtful.

We theorized that the NE of SBM is not greater than that of corn and that some essential amino acids (EAA) may have been limiting or in previous work conducted. We designed our trial to look at varying levels of SBM within the proven EAA to lysine ratios to be non-limiting on growing-finishing pig performance.

MATERIAL AND METHODS
A total of 2,153 pigs (PIC 337 × 1050; initially 28.8± 0.47 kg) were used in a 112-d growth trial. The study was conducted in two barns at a commercial research finishing site in southwest Minnesota. The barns were naturally ventilated and double-curtain-sided with totally slatted floors. Each pen was equipped with a 5-hole stainless steel dry self-feeder and a bowl waterer for ad libitum access to feed and water. All diets were manufactured at the Hord Farms West Feed Mill (Pipestone, MN) and were in mash form. Daily feed additions to each pen were accomplished using a robotic feeding system (FeedPro; Feedlogic Corp., Wilmar, MN) that recorded feed deliveries for individual pens. The protocol used in this experiment was approved by the Kansas State University Institutional Animal Care and Use Committee.

Pigs were housed in mixed gender pens with 26 or 27 pigs per pen across two barns. Pens of pigs were blocked by initial BW and allotted to 1 of 4 dietary treatments in a randomized complete block design with 20 pens per treatment. Soybean meal NE value used in diet formulation was 2,087 kcal/kg (78% NE of corn; NRC, 2012). The four treatments consisted of a diet containing a low level of SBM and added feed-grade amino acids (Low SBM) and three diets with 3.37 (Med-Low SBM), 6.69 (Med-High SBM), and 10% (High SBM) increase in SBM level compared to the Low SBM diet and decreased added feed-grade amino acids. The High SBM diet did not contain feed-grade L-lysine. Treatment diets were fed in four phases. Phase 1 and 4 diets are shown in tables 1 and 2, respectively. Pigs were weighed and feed disappearance was measured every 14 d to determine ADG, ADFI, and F/G. Caloric efficiency (CE) was determined on an NE basis and was calculated by multiplying total feed intake, kg × energy content of the diet (kcal/kg) and dividing by total kg of gain.

Three weeks prior to the end of the study, the 4 heaviest pigs in each pen were selected and marketed. The remaining pigs at the end of the study were tattooed with the specific pen identification number and marketed at a commercial abattoir (JBS Swift, Worthington, MN) for collection of carcass yield (carcass/live weight), BF, loin depth (LD), percentage lean, and hot carcass weight (HCW) for each individual carcass.

Experimental data were analyzed using the lmer function in R Studio (Version 4.2.2, R Core Team, Vienna, Austria) with pen serving as the experimental unit in a randomized complete block design within each of the two experimental barns. For all data, treatment served as a fixed effect within the statistical model, with the cross product of barn and block serving as a random effect. For carcass characteristics, pen was included as a random effect, and HCW was used as a covariate for all responses other than itself. Fixed effects were tested using the joint tests function in R, and treatment means were estimated using the emmeans function. Linear and quadratic contrasts were constructed with decreasing levels of SBM. Total removals and mortality data were analyzed assuming a binomial distribution with a logit link function. Results were considered significant at P ≤ 0.05 and marginally significant at P ≤ 0.10.

Results
Live performance data summarized by day 0 to 56, day 56 to 112 and over the entire trial (0 to 112) are shown in table 3 along with mortality, removals and carcass characteristics. Increasing the level of SBM and decreasing dietary FGAA linearly (P<0.004) decreased BW at both day 56 and 112. Hence, ADG was linearly (P<0.001) increased with increasing dietary levels of FGAA with decreasing SBM from day 0 to 56 and over the trial period (day 0 to 112), but only a tendancy for linear (P<.10) improvement was observed from day 56 to 112 interval. A linear (P<.004) increase in ADFI was observed in the day 0 to 56 period and over entire 112-day trial period with increasing dietary levels of FGAA, but not during the day 56 to 112 interval. A significant linear (P<.05) improvement for FCR was observed for increasing dietary levels of FGAA in the day 56 to 112 period, but not from day 0 to 56 or over the trial period.

CE was calculated for each diet using individual ingredient NE estimates from NRC (2012) then by multiplying total feed intake, kg × NE content of the diet (kcal/kg) and dividing by total kg of gain (live or carcass). As expected, using current NRC (2012) SBM NE estimates (2,087 kcal/kg), CE on a live weight basis was linearly (P<0.003) improved with increasing SBM, but not on a carcass basis (P=.146) due to decreased carcass weight observed with increasing levels of dietary SBM. Since FCR over the entire feeding period was not impacted (P=.246), an estimate of the NE of SBM was calculated by adjusting NE of SBM used in formulation (thus changing dietary NE) until CE for all treatments were equal. Estimated NE value of SBM was 93.5% on a liveweight basis and 83.9% on a carcass weight basis relative to the NE of corn based on this study results.

Carcass weight, yield percentage and ADG were linearly (P<0.001) increased with decreasing levels of SBM and consequential increase in dietary FGAA. Carcass FCR was also linearly (P<0.02) improved with increasing levels of FGAA. BF (P<.10) carcass lean percentage (P<.05) increased in a quadratic manner (P<.10) with increasing FGAA.

Interestingly, removals from treatment were linearly (P<.03) increased with increasing dietary levels of SBM. While mortality was unaffected (P>.41), however the combined removals and mortality percentage linearly (P<.01) increased with increasing levels of dietary SBM.

DISCUSSION
The current trial clearly demonstrates the live performance and carcass benefits of using FGAA instead of a corn-SBM only diet for growing finishing pigs.

These findings contrast with Cemin, et al. (2020) and Holen et al. (2022) who reported lower live performance with increasing FGAA with decreasing dietary SBM levels, though both sets of authors indicated formulating to NRC (2012) amino acid recommendations. However, there were no dietary adjustment or acknowledgment for phenylalanine, tyrosine or Arg levels. In a CJ sponsored trial (Williams et al. 2021) evaluating high FGAA levels in late nursery and early grower pigs, we observed equal BW and ADG when increasing dietary FGAA but could not maintain FCR. We speculate the increased ADFI observed with increasing FGAA was due to a co-limiting amino acid or nitrogen deficiency. This theory could help explain the lower performance observed by Cemin et al. (2020) and Holen et al. (2022) as the linear depression in growth in both experiments were primarily driven by the poor performance on the diets with the lowest level of SBM and highest level of FGAA.

Cemin et al. (2020) concluded “Using CE to estimate the energy of SBM relative to corn, a value of 105.4% of corn energy or 2816 kcal/kg NE was determined using all data points. When removing the CE value of the 39% SBM treatment due to the quadratic tendency, SBM was estimated to have 121.1% of corn energy or 3236 kcal/kg NE.” The authors attributed all the differences in growth and efficiency on the NE of SBM, not accounting for any other variables such potential amino acid deficiency. CE is a calculation of calculations, hence if any one of the assumptions are incorrect then the final calculation is incorrect.

The NE of SBM is likely higher than the NRC estimate of 2,087 kcal/kg. However, when evaluating net energy of SBM from biochemical and physiological approach, one cannot conclude SBM has equal or higher NE than corn. Recently Dr. Stein’s lab has employed the use of group housed indirect calorimetry to determine NE content of various feed ingredients. Stein (2024) reported on a trial evaluating the NE of US soybean meal and concluded a value of 2233 kcal/kg. This result is 83.6% of NRC (2012). This estimate of corn NE is very close to the calculated 83.9% relative to corn we observed on a carcass basis in the present study.

The use of FGAA is an important tool to lower feed cost while lowering nitrogen emission for swine and poultry producers. When FGAA’s are used within the known limits, they can improve animal performance and enhance carcass value. However, when lowering dietary crude protein via SBM or other protein sources, care must be taken as all the EAA ratios to SID Lys are not well established especially for 7th, 8th limiting amino acids and minimum nitrogen requirements for non-essential amino acid de novo synthesis. CE is a useful tool to examine dietary energy conversion to live weight or carcass. However, we must be cautious as total dietary NE is based on the sum of the individual ingredients which can be misleading. Results of this study support the idea that SBM NE is indeed higher than current NRC (2012) estimate. However, it does not suggest SBM NE is equal to or higher than corn.

References
1. Cemin, H., H.E. Williams, M.D. Tokach, S.S. Dritz, J.C. Woodward, J.M. DeRouchey, R.D. Goodband, K.F. Coble, B.A. Carrender and M.J. Gerhart. 2020. Estimate of the energy value of soybean
2. Meal relative to corn based on growth performance of nursery pigs. Journal of Animal Science and Biotechnology (2020) 11:70 https://doi.org/10.1186/s40104-020-00474-x
3. Holen, J.P., R.D. Goodband, M.D. Tokach, J.C. Woodward, J.M. DeRouchey and J.T. Gebhardt. 2022. Effects of increasing soybean meal in corn-based diets on the performance of late finishing pigs. Trans. Anim Sci. 7, 1-8. https://doi.org/10.1093/tas/txac165
4. NRC. 2012. Nutrient Requirements of Swine. 11th rev. ed. Natl. Acad. Press, Washington, DC.
5. Noblet, J and J. van Milgen. 2004. Energy value of pig feeds: Effect of pig body weight on energy evaluation system. J. Anim. Sci.82 (E Suppl.): E229-E238.
6. Stein, H.H Determination of net energy in U.S. soybean meal fed to group-housed pigs. https://nutrition.ansci.illinois.edu/node/1717
7. Stein, H.H. 2024. Net energy of soybean meal. J. Anim. Sci. Vol. 102, Suppl. S2 P184. Doi.org/10.1093/jas/skae102.205
8. Williams, H.R., M.D. Tokach, J.C. Woodward, J.M. DeRouchey, R.D. Goodband, J.T. Gebhart, C.W. Hastad, Z.B. Post and K.D. Haydon. 2021. Influence of feed grade amino acids level in late nursery and early grower diets fed to pigs from21 to 75 lb. Kansas Agricultural Experiment Station Research Reports: Vol. 7: Iss. 11. https://doi.org/10.4148/2378-5977.8218