Abstract
Soybeans are the primary protein ingredient source in poultry diets fed as soybean meals (SBM). In a typical corn-soy-based poultry (broiler) diet, SBM contributes up to 70% of dietary crude protein (CP), which dictates the significance of quantity and quality of protein/amino acids (AA) in SBM in dietary formulation. The objective of these studies was to evaluate different varieties of soybean from different maturity groups based on amino acid and protein digestibility in vitro and in-vivo experiments. The soybean varieties that are considered in this study were from different MGs, including MG 3, MG 4, MG 4.5, and MG 5, which are mostly grown in the southeastern region of the United States. First, an in vitro study was conducted using a multi enzyme approach mimicking broiler gut digestion processes to evaluate the digestibility of soybean meal (full-fat and defatted SBM) from 12 different varieties. Second, an in-vivo study with four varieties representing four different maturity groups was selected. A total of 144 birds (Cobb 500) were randomly divided into 4 dietary treatments in cages (six replicate cages per treatment). Semi-purified treatment diets were formulated as follows: TRT1, diet formulated with MG 3 soybean meal; TRT2, diet formulated with MG 4 soybean meal; TRT3, diet formulated with MG 4.5 soybean meal; and TRT4, diet formulated with MG 5 soybean meal. For both experiments, one-way ANOVA and Tukey’s multiple range test was conducted. The in-vitro results showed the highest digestibility values for amino acids for variety 7 of MG 4.5 group than other varieties (P < 0.05) for full-fat soybeans. The in vivo results showed that the feed conversion ratio (FCR) was lower in TRT3 and TRT4 groups compared to the TRT1 and TRT2 (P = 0.002). Both in-vitro and in-vivo findings implied that soybeans from MGs 4.5 and 5 could have favorable nutritional significance.
Key words: Soybean varieties, maturity group, amino acid digestibility, broilers
Introduction
Soybeans are the primary protein source in typical commercial poultry diets. According to the American Soybean Association (2022), poultry consumes 61% of the total soybean meal (SBM) used in livestock feed, followed by swine (17%), dairy (14%), and beef (5%). As a leguminous oilseed, soybeans are among the world’s most efficient plant-based protein sources (Nahashon and Kilonzo-Nthenge, 2011). The U.S. origin SBM contains approximately 47.5% crude protein (CP), though this could vary based on hull removal and oil extraction processes (Beski et al., 2015; Thakur and Hurburgh, 2007).
Selecting the optimal soybean variety is a key management decision for soybean farmers, affecting both yield and nutritional output. However, soybean varieties differ significantly, particularly in yield and maturity level, which are affected by environmental conditions like rainfall. Varieties are categorized by maturity group (MG), based on photoperiod and temperature sensitivity (Cober et al., 2001). The MGs help farmers choose the best-suited variety for their location and planting schedule, balancing yield potential and disease resistance. MGs, ranging from 0 to 8, align with geographic and climatic zones. Early maturing varieties require shorter nights, while late-maturing varieties need longer periods of darkness (Vann, 2021). For instance, MG 0 to 3 grow well in cooler regions with shorter seasons, whereas MG 4 to 8 are suited for warmer climates with longer growing seasons (Liu et al., 2017). A gradation system within each MG, such as MG 4.0 to 4.9, further refines the timing of flowering and maturation (Zhang et al., 2007). Generally, warmer climates allow soybeans to reach full maturity and achieve higher protein content. Soybeans are planted from April through early July, predominantly in the western and middle regions of the U.S. The MG 4 varieties dominate (about 70%), followed by MG 5 and 3.
To assess nutrient availability, in vitro digestion techniques are used. Multi-enzyme assays using pepsin and pancreatin simulate digestion and are effective for estimating protein and AA digestibility (Cave, 1988). Porcine pepsin and pancreatin are commercially available and widely used enzyme for protein and amino acid digestibility studies (Santos-Sánchez et al., 2024). This method is widely used to assess the quality of SBM, including variations due to under or over-heating during processing.
Despite the central role of soybeans in poultry nutrition, limited information is available regarding how genetic variation among soybean varieties influences nutrient composition and digestibility in poultry diets. This study evaluates the nutritional and digestibility variabilities of various soybean varieties grown in the U.S., focusing on crude protein and amino acid (AA) in full fat soybeans (FFS) and defatted SBM. Evaluating the digestibility variabilities specific to soybean varieties, the goal is to understand if any specific variety is more digestible than other varieties for broiler chickens.
Materials and methods
Experiment 1
Variety selection and seed preparation for of full fat soybean (FFS) meal and defatted soybean meal (SBM)
Twelve varieties of soybeans that were sourced from the Official Variety Testing Program of the University of Tennessee were chosen and evaluated based on each variety’s harvest year, yield, and MG levels. These soybean varieties were initially characterized by MG, yield, oil content, and moisture % (Table 1). Dried soybean variety seed samples were washed and dehulled, then ground and passed through a sieve approximately 2 mm for utilization of the multi-enzyme digestion assay that mimicked a broiler gut scenario. These samples were considered FFS meal. Additionally, another set of soybean seeds was washed, dehulled, and the oil was extracted (using a lab-scale expeller) to make defatted SBM. The seed preparation procedures were adapted from Boisen and Fernandez (1997); Noblet and Jaguelin-Peyraud (2007); Yegani et al. (2013), and modified as follows; Briefly, soybeans were soaked in UV-treated water (Synergy UV-R, ultrapure (Type 1) water) inside a glass beaker and placed on a heated stir plate at approximately 80-90℉ for 30 minutes. The beans were cooled to RT and dehulled manually by removing each shell from the seed. Then placed in an incubator oven at 70°C for several hours to dry before grinding to prepare FFS and placing in a sterile container. For SBM preparation, dehulled and dried soybeans were run through a commercial oil press machine (ASIN# B094VN5Y8, China) for extraction of oil.
Table 1.
| Variety | Relative Maturity | Maturity Group | Yield, MT | Protein, % | Oil,% | Moisture,% |
|---|---|---|---|---|---|---|
| V1 | 3.9 | MG3 | 51.8773 | 39.83 | 22.73 | 5.89 |
| V2 | 3.9 | MG3 | 51.8773 | 41.14 | 22.79 | 6.09 |
| V3 | 3.9 | MG3 | 49.5231 | 38.16 | 24.26 | 6.64 |
| V4 | 4.3 | MG4E | 52.8698 | 40.47 | 22.63 | 6.95 |
| V5 | 4.5 | MG4E | 56.7179 | 40.06 | 21.57 | 6.76 |
| V6 | 4.5 | MG4E | 55.258 | 39.95 | 23.28 | 6.84 |
| V7 | 4.9 | MG4L | 57.5258 | 38.96 | 23.28 | 6.64 |
| V8 | 4.6 | MG4L | 60.0329 | 38.14 | 22.33 | 6.95 |
| V9 | 4.9 | MG4L | 58.9177 | 40.58 | 22.14 | 7.18 |
| V10 | 5.1 | MG5 | 54.9876 | 39.75 | 22.64 | 7.23 |
| V11 | 5.1 | MG5 | 54.9876 | 41.15 | 22.95 | 6.75 |
| V12 | 5.3 | MG5 | 52.0153 | 38.42 | 22.73 | 6.63 |
Values (Relative Maturity, Maturity Group, Yield) collected from Soybean Variety Testing facility in Knoxville, TN.
Relative maturity refers to the maturity of each sample. MG3 is 3.0-3.9, MG4E is 4.0-4.5, MG4L is 4.5-4.9, and MG5 is 5.0-5.9, respectively.
NIR (near infrared spectrometry) values generated for Oil and Protein content.
Experimental procedure: In-vitro digestion assay
This experimental procedure was adapted from (Boisen and Eggum, 1991; Boisen and Fernandez, 1997; Noblet and Jaguelin-Peyraud, 2007) with slight modifications. Twelve soybean samples, processed to produce FFS and SBM as described earlier, each consisting of 1.5 g of finely ground material, were sieved and weighed with an accuracy of ± 0.1 mg using 125-ml sterile flasks. Each sample was evaluated in triplicate. A magnetic rod was placed into each flask, and 25 ml of 0.1 M phosphate buffer solution was added. Subsequently, 10 ml of 0.2 M HCl was added to reduce the pH from 6 to 2.4. 1 M HCl and 1 M NaOH were added to adjust the pH as necessary. Then, 1 ml of porcine pepsin (Sigma Aldrich, P7000-100 G) at 25mg/ml per ultra-pure water were added to the solution. Flasks were swirled and placed into a controlled incubator shaker (New Brunswick Innova40 Incubator Shaker Series, model M1299-0090,) at 41°C and 150 rpm for 2 hours. This was to simulate the condition of the crop and gastric phase of digestion.
After the incubation, the flask was removed from the incubator shaker and 10 ml of 0.2 M phosphate buffer and 5 ml of 0.6 M NaOH solution were added. This was to raise the flask pH to 6.6-6.8, respectively. Once swirled, freshly prepared 1 ml of porcine pancreatin (Sigma Aldrich, powder. P3292-25 G) containing 100 mg/ml of pancreatin per ml of ultra-pure water was added. Flasks were swirled once more, sealed, and added back to the controlled incubator shaker with the same temperature and speed for 4 hours. This step was intended to simulate the post gastric ileal phase of the intestinal digestion.
Once complete, the final digestion stage, the magnetic stir rods were removed, and the sample mixture was filtered using Whatman no 4 (Whatman 4 filter paper CAT No. 1004-150) filter papers. The in vitro residue was collected onto a sterile petri dish and dried overnight at 75°C. The samples were then shipped to the University of Missouri-Columbia Chemistry Lab for CP and AA profile.
Measurement of rate of disappearance (RD)
The rate of CP and AA disappearance was calculated for each sample utilizing the following equation:
RD = 1- (R/I); with I- the content of CP or a specific AA in the initial sample, R- the content of CP or a specific AA in the residual sample (Witten and Aulrich, 2022).
Experiment 2: In-vivo broiler assay
The in-vivo broiler experiment followed all the procedures according to institutional animal care and use committee of Tennessee State University.
Soybean variety sources and preparation for experimental diets
Four varieties of soybean cultivars were provided by two commercial companies through University of Tennessee, Knoxville. The varieties represented MGs 3, 4, 4.5 and 5. Due to limited resources, soybeans were not dehulled. The oil was extracted with a commercial oil pressure machine (ASIN# B094VN5Y8, AYLYOTOY, China) at 70°C. The SBM was then manually ground into finely small crumbles.
Birds, diets and housing
One-day old 240 chicks (males) of average body weight (BW) 40 ± 4 g was obtained from Cobb Vantress Hatchery, Layfette, TN. They were randomly divided into 24 cages (10 birds/cage). Cage dimensions were 108 cm in length, 108 cm wide and 35 cm in height. All cages were allotted into different treatment groups, as each group containing 6 replicate cages. For d0-10, they were raised on a common starter diet (Supplementary file) formulated according to nutrition guidelines for the breed (Cobb-Vantress, 2022). For the 1st week, room temperature was kept at 90°F, 2nd week 85°F and 3rd week 80°F. Birds were provided with 24 h of light on d0, 23 h of light and 1 h of darkness/d from d1 to 3, followed by 18 h of light and 6 h of darkness/d until d22. The diets were fed in mash form and provided. Water was also provided throughout the experiment. Feed and water access were as ad libitum. The d10-22 was the experimental phase. On d10, a total of 144 birds were selected (200±12 g) and distributed to 4 dietary treatments with 6 replication cages with 6 birds per cage Semi-purified diets (Table 6) were formulated according to Cobb 500 nutrient requirement (Cobb-Vantress, 2022). Dietary treatments that were provided to birds from d10-22, were TRT1, formulated with MG 3.0 SBM; TRT2, MG 4 SBM; TRT3, MG 4.5 SBM; and TRT4, MG 5 SBM.
Table 6.
Composition and analyzed nutrient composition of treatment diets1.
| Feed ingredient, % | TRT1 | TRT2 | TRT3 | TRT4 |
|---|---|---|---|---|
| Soybean meal | ||||
| Variety 1 | 41.58 | |||
| Variety 2 | 41.58 | |||
| Variety 3 | 41.58 | |||
| Variety 4 | 41.58 | |||
| Corn starch | 48.77 | 48.77 | 48.77 | 48.77 |
| Dicalcium phosphate | 3.68 | 3.68 | 3.68 | 3.68 |
| Lysine HCL | 2 | 2 | 2 | 2 |
| DL-methionine | 1.5 | 1.5 | 1.5 | 1.5 |
| Salt (NaCl) | 0.36 | 0.36 | 0.36 | 0.36 |
| Soybean oil | 2 | 2 | 2 | 2 |
| Vitamin-mineral premix 3% | 0.1 | 0.1 | 0.1 | 0.1 |
| Titanium dioxide | 0.05 | 0.05 | 0.05 | 0.05 |
| Analyzed nutrient composition | ||||
| Calories (calories/100 g) | 384 | 371 | 377 | 376 |
| Crude protein, % | 19.48 | 19.39 | 20.11 | 19.32 |
| Moisture, % | 7.37 | 7.93 | 7.28 | 7.24 |
| Crude Fat, % | 6.92 | 5.19 | 5.91 | 6.05 |
| Crude Fiber, % | 13.60 | 16.41 | 16.84 | 15.50 |
| Ash, % | 5.36 | 5.74 | 5.95 | 6.41 |
| Amino acids | ||||
| Arginine | 1.02 | 0.94 | 1.18 | 1.11 |
| Histidine | 0.40 | 0.38 | 0.47 | 0.46 |
| Isoleucine | 0.72 | 0.65 | 0.81 | 0.78 |
| Leucine | 1.15 | 1.08 | 1.30 | 1.25 |
| Methionine | 1.78 | 1.80 | 1.85 | 1.80 |
| Phenylalanine | 0.75 | 0.69 | 0.86 | 0.82 |
| Threonine | 0.57 | 0.53 | 0.66 | 0.65 |
| Valine | 0.72 | 0.66 | 0.81 | 0.78 |
| Lysine | 2.05 | 1.86 | 2.97 | 2.59 |
| Alanine | 0.65 | 0.62 | 0.74 | 0.72 |
| Aspartic Acid | 1.67 | 1.52 | 1.94 | 1.83 |
| Glutamic Acid | 2.73 | 2.57 | 3.18 | 2.99 |
| Proline | 0.73 | 0.71 | 0.84 | 0.81 |
| Serine | 0.66 | 0.61 | 0.77 | 0.73 |
| Tyrosine | 0.51 | 0.47 | 0.60 | 0.58 |
| Tryptophan | 0.21 | 0.14 | 0.20 | 0.23 |
Four experimental diets were formulated: TRT1, diet containing soybeans from MG 3; TRT2, diet containing soybeans from MG 4, TRT3, containing soybeans from Mg 4.5; TRT4, containing soybeans from MG 5.
Bird performance and sample collection for digestibility assay
Body weight was measured at days 0, 10 and 22 with daily FI records. For the period of day 10-22, body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) were measured.
For digestibility analysis, 0.5% TiO2 was added to the diet from d11 to 23. On d23, 3 birds/cage were sacrificed using CO2 gas inhalation method to collect the ileal digesta. The contents of the lower half of the ileum to the ileocecal junction (digesta) were removed by gently squeezing. Samples were put on ice immediately after collection, then frozen and stored at −20°C. The digesta samples were freeze dried. The diet and freeze-dried digesta samples were finely ground to pass through a 0.5-mm sieve and stored at 4°C in until analysis. The diet and digesta samples were sent to Missouri Feed Labs (Experimental Station Chemical Laboratories, University of Missouri-Columbia, Columbia, MO), for titanium and nutrient analysis. Titanium was analyzed according to Fowler et al. (2022). For titanium analysis, from each sample 0.15 g were ashed overnight and mixed with deionized water. Subsequently, 1 g of ammonium sulfate and 13 mL of sulfuric acid was added to the mixture and digested at 420°C for 3 h. After digestion, 10 mL of 30% hydrogen peroxide was mixed with the solution and the absorbance was read at 410 nm (Genesys 10S UV-Vis; Thermo Fisher Scientific, Waltham, MA, USA). The apparent ileal digestibility (AID) of AAs was calculated using the following formula (Nyachoti et al., 1997):
| AIDAA (%) = 100-[100*(AAdigesta*TiO2diet)/(AAdiet*TiO2digesta) |
Where AAdigesta and AAdiet were the concentrations of AA in the digesta and diet, respectively, and TiO2diet and TiO2digesta represented the concentrations of the indigestible marker titanium dioxide in the diet and digesta, respectively. Both AA and titanium dioxide concentrations in the diet and digesta were measured in mg/kg DM.
Statistical analysis
For in-vitro and in-vivo experiments, variables such as CP, AAs, and digestibility coefficient values for each CP or AA were measured in terms of mean values for each variety or treatment group. Soybean varieties and MG were considered as the fixed effects. Data was tested for normality, and all data was within normal distribution. For both experiments, one-way ANOVA was conducted using SAS (SAS institute, 9.4). Tukey’s multiple range test was conducted to identify the treatment group differences. For in vivo experiment, each sample was experimental unit with three replications for each sample. For in vitro experiment, replicate cage was experimental unit for growth performance (six cage per treatment) and ileal sample from each bird (six sample per treatment) for amino acid digestibility were the experimental unit. Means were considered significant if P-value is ≤ 0.05.
Results and discussion
Experiment 1
Crude protein and amino acid profile of soybean varieties
Table 2 represents the CP and AA values of FFS tested in the in-vitro digestibility experiment. Protein and AA values of the tested SBM are shown in Table 3. Notable variability existed in CP and AA content in the FFS meal among varieties (Table 2). Varieties V1, V5, V7, V9, V10, and V11 had numerically higher CP and total AA contents, with these varieties (except V5) having higher lysine concentrations. Methionine and threonine levels were relatively stable across all varieties.
Table 2.
Amino acid (AA) and Crude Protein (CP) profile of full fat soybean (FFS) varieties utilized in the in-vitro digestion study (‘as is’ values)1.
| Variety | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | V9 | V10 | V11 | V12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hydroxyproline | 0 | 0 | 0.05 | 0.03 | 0.03 | 0.00 | 0.04 | 0.03 | 0.03 | 0.02 | 0.03 | 0.04 |
| Aspartic Acid | 5.22 | 4.99 | 4.76 | 4.79 | 5.2 | 4.91 | 5.08 | 4.93 | 5.25 | 5.11 | 5.13 | 4.8 |
| Threonine | 1.74 | 1.69 | 1.7 | 1.62 | 1.78 | 1.68 | 1.75 | 1.73 | 1.8 | 1.79 | 1.76 | 1.7 |
| Serine | 1.93 | 1.9 | 1.92 | 1.79 | 1.93 | 1.89 | 1.94 | 1.89 | 2.05 | 2.01 | 1.95 | 1.81 |
| Glutamic Acid | 8.38 | 7.97 | 7.37 | 7.59 | 8.22 | 7.68 | 7.97 | 7.67 | 8.32 | 8.01 | 8.07 | 7.5 |
| Proline | 2.27 | 2.18 | 2.09 | 2.1 | 2.29 | 2.10 | 2.23 | 2.15 | 2.32 | 2.23 | 2.27 | 2.14 |
| Glycine | 1.93 | 1.85 | 1.75 | 1.77 | 1.95 | 1.80 | 1.92 | 1.86 | 1.99 | 1.9 | 1.91 | 1.84 |
| Alanine | 1.96 | 1.88 | 1.85 | 1.8 | 1.99 | 1.85 | 1.95 | 1.91 | 1.98 | 1.95 | 1.97 | 1.9 |
| Cysteine | 0.6 | 0.6 | 0.58 | 0.58 | 0.68 | 0.61 | 0.61 | 0.65 | 0.68 | 0.66 | 0.68 | 0.63 |
| Valine | 2.4 | 2.28 | 2.14 | 2.2 | 2.42 | 2.19 | 2.39 | 2.29 | 2.41 | 2.33 | 2.39 | 2.29 |
| Methionine | 0.63 | 0.61 | 0.58 | 0.59 | 0.66 | 0.61 | 0.63 | 0.65 | 0.66 | 0.63 | 0.65 | 0.63 |
| Isoleucine | 2.29 | 2.18 | 2.09 | 2.13 | 2.32 | 2.14 | 2.26 | 2.2 | 2.29 | 2.23 | 2.29 | 2.18 |
| Leucine | 3.58 | 3.44 | 3.38 | 3.34 | 3.59 | 3.36 | 3.56 | 3.44 | 3.61 | 3.55 | 3.58 | 3.37 |
| Tyrosine | 1.75 | 1.7 | 1.66 | 1.6 | 1.73 | 1.63 | 1.69 | 1.7 | 1.73 | 1.73 | 1.72 | 1.65 |
| Phenylalanine | 2.4 | 2.31 | 2.27 | 2.22 | 2.4 | 2.21 | 2.37 | 2.27 | 2.42 | 2.36 | 2.38 | 2.22 |
| Hydroxylysine | 0 | 0 | 0 | 0 | 0 | 0.00 | 0 | 0 | 0 | 0 | 0 | 0 |
| Lysine | 3.05 | 2.92 | 2.85 | 2.82 | 3.1 | 2.89 | 3.03 | 2.98 | 3.07 | 3.04 | 3.08 | 2.95 |
| Histidine | 1.34 | 1.27 | 1.23 | 1.21 | 1.32 | 1.21 | 1.31 | 1.27 | 1.3 | 1.32 | 1.33 | 1.28 |
| Arginine | 3.45 | 3.24 | 3.17 | 3.11 | 3.38 | 3.11 | 3.28 | 3.18 | 3.39 | 3.33 | 3.35 | 3.11 |
| Tryptophan | 0.41 | 0.45 | 0.42 | 0.39 | 0.56 | 0.47 | 0.62 | 0.52 | 0.59 | 0.43 | 0.53 | 0.41 |
| Total amino acid | 45.43 | 43.54 | 41.95 | 41.77 | 45.65 | 42.46 | 44.72 | 43.42 | 45.98 | 44.72 | 45.18 | 42.54 |
| Crude Protein | 40.55 | 38.18 | 36.79 | 34.84 | 40.63 | 38.97 | 39.05 | 37.66 | 40.10 | 39.93 | 40.05 | 37.70 |
W/W%= grams per 100 grams of sample. Crude protein*= %N x6.25. V, variety; MG, maturity group. V1 to V3 belongs to MG3, V4 to V6 belongs to MG 4, V7 to V9 belongs to MG 4.5 and V10 to V12 belongs to MG 5 groups.
Table 3.
Crude protein (CP) and amino acid (AA) profile of soybean meal (SBM) varieties utilized in the in-vitro digestion study (‘as is’ values, )1.
| Item, % | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | V9 | V10 | V11 | V12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Taurine | 0.12 | 0.12 | 0.13 | 0.12 | 0.12 | 0.12 | 0.13 | 0.15 | 0.13 | 0.13 | 0.12 | 0.13 |
| Hydroxyproline | 0.07 | 0.08 | 0.08 | 0.06 | 0.07 | 0.07 | 0.08 | 0.07 | 0.00 | 0.08 | 0.07 | 0.07 |
| Aspartic Acid | 6.64 | 6.38 | 6.13 | 6.29 | 6.48 | 6.39 | 6.01 | 5.94 | 6.60 | 6.44 | 6.35 | 6.00 |
| Threonine | 2.23 | 2.16 | 2.10 | 2.15 | 2.22 | 2.17 | 2.08 | 2.07 | 2.25 | 2.21 | 2.19 | 2.11 |
| Serine | 2.45 | 2.37 | 2.30 | 2.34 | 2.38 | 2.37 | 2.29 | 2.17 | 2.46 | 2.43 | 2.38 | 2.32 |
| Glutamic Acid | 10.83 | 10.34 | 9.77 | 10.10 | 10.43 | 10.26 | 9.60 | 9.31 | 10.63 | 10.39 | 10.14 | 9.64 |
| Proline | 2.88 | 2.78 | 2.66 | 2.74 | 2.82 | 2.77 | 2.62 | 2.56 | 2.87 | 2.82 | 2.79 | 2.62 |
| Glycine | 2.44 | 2.36 | 2.27 | 2.33 | 2.42 | 2.37 | 2.25 | 2.22 | 2.44 | 2.40 | 2.35 | 2.26 |
| Alanine | 2.50 | 2.42 | 2.36 | 2.39 | 2.48 | 2.43 | 2.32 | 2.29 | 2.49 | 2.46 | 2.42 | 2.32 |
| Cysteine | 0.79 | 0.76 | 0.76 | 0.79 | 0.84 | 0.80 | 0.76 | 0.76 | 0.87 | 0.86 | 0.86 | 0.80 |
| Valine | 2.94 | 2.84 | 2.73 | 2.81 | 2.90 | 2.86 | 2.68 | 2.64 | 2.92 | 2.86 | 2.81 | 2.66 |
| Methionine | 0.78 | 0.75 | 0.73 | 0.77 | 0.81 | 0.78 | 0.74 | 0.74 | 0.82 | 0.80 | 0.79 | 0.76 |
| Isoleucine | 2.89 | 2.77 | 2.68 | 2.77 | 2.84 | 2.80 | 2.63 | 2.59 | 2.86 | 2.79 | 2.75 | 2.60 |
| Leucine | 4.55 | 4.38 | 4.24 | 4.36 | 4.45 | 4.39 | 4.16 | 4.06 | 4.50 | 4.41 | 4.35 | 4.13 |
| Tyrosine | 2.11 | 2.02 | 1.96 | 2.01 | 2.08 | 2.03 | 1.92 | 1.94 | 2.12 | 2.05 | 2.05 | 1.95 |
| Phenylalanine | 3.03 | 2.91 | 2.83 | 2.88 | 2.96 | 2.90 | 2.75 | 2.67 | 2.99 | 2.91 | 2.89 | 2.73 |
| Hydroxylysine | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Lysine | 3.70 | 3.58 | 3.44 | 3.62 | 3.70 | 3.62 | 3.46 | 3.41 | 3.73 | 3.70 | 3.66 | 3.50 |
| Histidine | 1.59 | 1.54 | 1.48 | 1.53 | 1.57 | 1.55 | 1.47 | 1.45 | 1.58 | 1.58 | 1.56 | 1.49 |
| Arginine | 4.16 | 3.99 | 3.86 | 3.92 | 4.09 | 3.98 | 3.72 | 3.71 | 4.16 | 4.06 | 4.02 | 3.77 |
| Tryptophan | 0.83 | 0.80 | 0.78 | 0.81 | 0.84 | 0.84 | 0.76 | 0.77 | 0.84 | 0.80 | 0.78 | 0.74 |
| Total AA | 57.62 | 55.44 | 53.37 | 54.87 | 56.59 | 55.58 | 52.52 | 51.60 | 57.35 | 56.27 | 55.41 | 52.67 |
| Crude Protein | 51.95 | 50.70 | 48.46 | 49.35 | 51.27 | 50.46 | 47.69 | 45.53 | 51.61 | 50.70 | 49.38 | 47.54 |
W/W%= grams per 100 grams of sample. Crude protein*= %N x6.25. V, variety; MG, maturity group. V1 to V3 belongs to MG3, V4 to V6 belongs to MG 4, V7 to V9 belongs to MG 4.5 and V10 to V12 belongs to MG 5 groups.
In-vitro digestion assay
The rate of disappearance (RD) of CP and AAs in FFS differed significantly among varieties (Table 4). Variety V7, from MG 4.5, exhibited the highest RD for CP (64.5%), followed by V11 (53.4%). Similarly, V7 showed the highest RD for essential AAs (arginine, histidine, leucine, methionine, phenylalanine, threonine, valine, and lysine), with similar values in V8, V9, V10, V11, and V12 groups. In contrast, V1 and V4 showed the lowest RD for CP and AA. Based on these findings, V7 FFS appears to have the most favorable protein digestibility profile, suggesting its greater suitability as a broiler feed ingredient.
Table 4.
Crude protein (CP), total and individual amino acids (AA) disappearance values post enzymatic digestion for full fat soybean (FFS) varieties1.
| Variety | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | V9 | V10 | V11 | V12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CP, % | 39.6 | 47.8bcd | 41.9bcd | 37.4d | 41.8bcd | 38.9cd | 64.5a | 47.6bcd | 44.4bcd | 49.8bc | 53.4ab | 48.5bcd |
| Total AA, % | 45.43 | 43.54 | 41.95 | 41.77 | 45.65 | 42.46 | 44.72 | 43.42 | 45.98 | 44.72 | 45.18 | 42.54 |
| Arginine | 39.9de | 52.1bc | 47.4bcde | 45.2cde | 43.6cde | 37.7e | 69.2a | 49.6bcd | 52.3bc | 51.8bc | 58.1b | 50.1bcd |
| Histidine | 34.1e | 46.2bc | 43.1bcde | 42.7bcde | 40.9cde | 34.4de | 62.3a | 45.9bcd | 46.7bc | 47.7bc | 54.1ab | 49.5bc |
| Isoleucine | 27.8f | 40.5de | 38.4def | 40.8de | 33.9ef | 28.8f | 55.2bc | 43.2de | 46cd | 63.8ab | 70.6a | 65.2ab |
| Leucine | 26.4d | 40.8c | 40.9c | 42.1c | 42.8bc | 37.5cd | 55.6a | 43.6bc | 48.2abc | 43.7bc | 53.5ab | 45.3abc |
| Methionine | 31.7c | 46.4ab | 42bc | 44.6ab | 48.5ab | 47.5ab | 56.1a | 48.2ab | 51.5ab | 45.5ab | 54.9a | 49.2ab |
| Phenylalanine | 27.9d | 43bc | 42.6bc | 42.5bc | 33.8cd | 29d | 57.7a | 44.8bc | 44.9ab | 45.3abc | 54.5ab | 46.1abc |
| Threonine | 36cde | 41.6bcde | 41.2bcde | 39.5bcde | 33.9de | 31.3e | 58.1a | 42bcde | 46.3bc | 43.9bcd | 50.9ab | 45bcd |
| Valine | 29ef | 41.8cd | 38.2cdef | 39.8cde | 33.9def | 27.9f | 56.2a | 44bcd | 46.6abc | 42.9bcd | 53.4ab | 45.4abcd |
| Lysine | 37.2d | 48.1bc | 43.9cd | 42.1cd | 42.8cd | 37.5d | 65.8a | 46.6bcd | 49bc | 48bc | 54.7b | 48.1bc |
| Alanine | 30.4de | 39.5bcde | 37.7cde | 37.6cde | 33.4cde | 30.3e | 53.7a | 40.3bcde | 42.9bc | 40.9bcd | 48.4ab | 42.6bc |
| Aspartic Acid | 36.8d | 47.8bcd | 43.3cd | 42.7cd | 40.3cd | 37d | 65.6a | 46.7bcd | 50.1bc | 48.7bc | 55.8ab | 48.3bc |
| Glutamic Acid | 43.4e | 54.7bcd | 48.4cde | 47.1cde | 47.9cde | 44de | 72.9a | 51.8bcde | 55.1bc | 54.1bcde | 60.8b | 53.6bcde |
| Proline | 33.5d | 45.7bc | 41.8bcd | 40.6bcd | 37.8cd | 33.3d | 61.6a | 44.5bcd | 47.4bc | 45.4bc | 51.4ab | 45.4bc |
| Serine | 26.3d | 38.1bcd | 37.8bcd | 35.6bcd | 32.1cd | 31.2cd | 55.4a | 36.5bcd | 42.6bc | 40.8bc | 45.6ab | 39.6bc |
| Tyrosine | 36.4c | 43.5bc | 41.4c | 39.6c | 39.3c | 36.6c | 58.2a | 42.7bc | 44.5bc | 45.1bc | 52.9ab | 46.9bc |
V1 to V3 belongs to maturity group (MG) 3, V4 to V6 belongs to MG 4, V7 to V9 belongs to MG 4.5 and V10 to V12 belongs to MG 5 groups.
Means within a row followed by a different letter (a-f) are significantly different (P ≤ 0.05).
In contrast, the RD values for CP and AAs in SBM derived from different varieties (Table 5) did not show significant differences among the groups. This lack of variation could be attributed to the limited replication, which may have reduced the statistical power to detect differences.
Table 5.
Rate of disappearance for Crude protein (CP), and individual amino acids in SBM by varieties*.
| Variety | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | V9 | V10 | V11 | V12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CP, % | 48.7 | 51.9 | 53.1 | 51.7 | 52.5 | 53.0 | 49.5 | 49.7 | 50.6 | 50.4 | 49.5 | 48.9 |
| Individual AA | 57.62 | 55.44 | 53.37 | 54.87 | 56.59 | 55.58 | 52.52 | 51.60 | 57.35 | 56.27 | 55.41 | 52.67 |
| Arginine | 50.5 | 54.1 | 57.0 | 55.9 | 57.0 | 56.0 | 54.8 | 55.3 | 53.6 | 53.7 | 53.7 | 52.5 |
| Histidine | 47.8 | 53.2 | 54.1 | 52.3 | 52.9 | 52.9 | 53.7 | 53.8 | 51.9 | 52.5 | 50.6 | 49.0 |
| Isoleucine | 45.3 | 50.9 | 52.2 | 48.4 | 49.3 | 49.6 | 52.5 | 51.0 | 50.0 | 49.5 | 46.2 | 46.2 |
| Leucine | 44.2 | 50.0 | 50.7 | 47.0 | 48.1 | 48.3 | 51.2 | 48.8 | 48.7 | 49.0 | 45.3 | 45.0 |
| Methionine | 59.0 | 57.3 | 63.0 | 61.0 | 63.0 | 60.3 | 56.8 | 58.1 | 58.5 | 58.8 | 53.2 | 53.9 |
| Phenylalanine | 46.2 | 51.5 | 52.7 | 49.3 | 50.0 | 50.0 | 52.4 | 51.3 | 50.2 | 50.5 | 48.1 | 47.3 |
| Threonine | 44.4 | 49.5 | 50.0 | 47.4 | 48.6 | 48.4 | 50.0 | 48.8 | 48.0 | 48.4 | 45.7 | 45.0 |
| Valine | 43.5 | 49.3 | 50.2 | 46.3 | 47.2 | 47.6 | 50.4 | 48.9 | 47.9 | 47.6 | 43.8 | 43.6 |
| Lysine | 48.4 | 52.5 | 54.1 | 53.3 | 54.1 | 53.6 | 53.5 | 53.4 | 51.5 | 51.6 | 51.4 | 50.3 |
| Alanine | 42.8 | 47.5 | 48.7 | 45.2 | 45.6 | 46.1 | 48.7 | 47.6 | 45.4 | 45.9 | 43.4 | 43.1 |
| Aspartic Acid | 51.5 | 55.2 | 57.1 | 56.6 | 57.4 | 57.0 | 56.4 | 56.7 | 54.1 | 54.5 | 54.5 | 53.7 |
| Glutamic Acid | 55.0 | 57.5 | 60.5 | 61.0 | 62.2 | 61.0 | 59.4 | 59.1 | 57.2 | 58.0 | 58.9 | 58.6 |
| Proline | 45.5 | 50.7 | 51.1 | 50.0 | 50.0 | 50.2 | 50.0 | 50.4 | 48.1 | 48.9 | 48.4 | 46.9 |
| Serine | 44.9 | 48.9 | 50.0 | 49.1 | 49.2 | 49.4 | 48.0 | 45.2 | 46.7 | 49.0 | 46.2 | 46.1 |
| Tyrosine | 50.2 | 53.5 | 56.1 | 54.2 | 55.8 | 54.7 | 54.2 | 55.7 | 52.8 | 52.7 | 53.2 | 51.8 |
V1 to V3 belongs to MG3, V4 to V6 belongs to MG 4, V7 to V9 belongs to MG 4.5 and V10 to V12 belongs to MG 5 groups.
The CP and AA compositions observed in this study are within the range of values reported for U.S. produced soybean and SBM products (Baker and Stein, 2009; Frikha et al., 2012; Grieshop et al., 2003; Lagos and Stein, 2017). The U.S. soybean products generally have higher CP and essential AA concentrations compared to soybeans produced in other regions (Ravindran et al., 2014). Among tested FFS V1, V5, V7, V9, V10 and V11 had higher total amino acids (TAA) and lysine content ranging from 44.72 to 45.65% and 3.03-3.1% respectively. The methionine and threonine content of all FFS varieties were almost similar ranging from 0.58 to 0.61% and 1.7-1.8%, respectively. In case of SBM varieties, V1, V2, V4, V5, V6, V9, V10, and V11 had higher TAA ranging from 54.9 to 57.62% and higher lysine content ranging from 3.58 to 3.70%. The methionine and threonine content of different SBM varieties were similar ranging from 0.73 to 0.82% and 2.07-2.25% respectively. Given that AAs are the structural and functional units of protein, their adequate supply plays a critical role in broiler physiology, growth, muscle development, and immune function (Bortoluzzi et al., 2018; Leeson et al., 1996). Diets with higher AA availability improve growth performance, feed efficiency, and gut health, and may reduce heat stress in broilers (Baxter et al., 2020; Chrystal et al., 2020). Among essential AAs, lysine and methionine are the first two limiting AA, followed by threonine (Corzo et al., 2007; Kidd and Kerr, 1996).
Experiment 2
Growth performance results for broilers fed diets formulated with different MG for SBMs are shown in Table 7. FI was significantly higher in TRT2, TRT3, and TRT4 compared to TRT1 (P < 0.001). Although BW and BWG did not differ among treatment groups (P > 0.05), TRT3 and TRT4 had improved FCR values compared to TRT1 and TRT2 (P = 0.002), indicating better feed efficiency.
Table 7.
| Day 10-22 (Treatment period) |
||||||
|---|---|---|---|---|---|---|
| Item | BW d 0, g | BW d 10, g | BW d 22, g | FI, g | BWG, g | FCR |
| TRT1 | 39.2 | 209 | 350 | 336b | 141 | 2.47a |
| TRT2 | 39 | 205 | 349 | 350a | 144 | 2.43a |
| TRT3 | 39.1 | 216 | 381 | 368a | 165 | 2.23b |
| TRT4 | 39 | 215 | 384 | 365a | 169 | 2.16b |
| SEM | 0.51 | 5 | 11 | 10 | 11 | 0.14 |
| P value | 0.719 | 0.403 | 0.089 | <0.001 | 0.169 | 0.002 |
Abbreviations: BW, body weight; FI, feed intake; BWG, body weight gain, FCR, feed conversion ratio. Semi purified diets were formulated using SBM from different maturity groups (MG). TRT1, MG3 diet; TRT2, MG4 diet; TRT3, MG4.5 diet; TRT4, MG5 diet.
Means within a column followed by a different letter are significantly different (P ≤ 0.05).
The digestibility of ileal AAs for SBM varieties is presented in Table 8. TRT3 and TRT4 diets had higher lysine digestibility (P = 0.034) compared to TRT1. Interestingly, only lysine digestibility was significantly improved, and other AA digestibility was not impacted. This discrepancy may be due to ingredient interactions and the complexity of the complete diet in the in vivo experiment. Feed matrix effects, nutrient-nutrient interactions, or passage rate differences may have influenced the actual digestibility in broilers (Lemme et al., 2004).
Table 8.
| Variety | TRT1 | TRT2 | TRT3 | TRT4 | SEM | P-value |
|---|---|---|---|---|---|---|
| Total AA | 41.6 | 57.7 | 57.4 | 60.1 | 1.2 | 0.352 |
| Essential AA | ||||||
| Arginine | 52.2 | 67.7 | 65.3 | 66.6 | 1.4 | 0.235 |
| Histidine | 43.3 | 56.8 | 57.3 | 60.3 | 1.3 | 0.798 |
| Isoleucine | 19.4 | 41.2 | 37.4 | 41.9 | 1.4 | 0.125 |
| Leucine | 25.9 | 46.9 | 43.4 | 47.8 | 1.5 | 0.307 |
| Methionine | 91.8 | 94.3 | 93.2 | 93.4 | 1.8 | 0.172 |
| Phenylalanine | 31.6 | 53.1 | 50.1 | 53.1 | 1.3 | 0.600 |
| Threonine | 0.7 | 27.1 | 29.9 | 36.8 | 1.3 | 0.459 |
| Valine | 17.1 | 38.8 | 35.9 | 38.8 | 2.0 | 0.712 |
| Lysine | 74.9b | 81.8ab | 85.0 a | 84.8a | 1.7 | 0.034 |
| Nonessential AA | ||||||
| Alanine | 27.7 | 46.4 | 44.6 | 49.2 | 1.8 | 0.125 |
| Aspartic Acid | 31.0 | 50.3 | 48.8 | 52.5 | 1.2 | 0.910 |
| Glutamic Acid | 55.9 | 70.3 | 68.8 | 71.2 | 2.4 | 0.150 |
| Proline | 30.2 | 49.6 | 49.6 | 51.9 | 1.1 | 0.552 |
| Serine | 17.5 | 39.2 | 41.0 | 45.5 | 1.5 | 0.796 |
| Tyrosine | 16.3 | 36.6 | 38.1 | 42.7 | 1.8 | 0.651 |
Abbreviations: TRT1, MG3 diet; Semi purified diets were formulated using SBM from different maturity groups (MG). TRT2, MG4 diet; TRT3, MG4.5 diet; TRT4, MG5 diet.
Means within a column followed by a different letter are significantly different (P ≤ 0.05).
There are very limited studies that examined the impact of soybean MG on broiler growth performance, making this a novel aspect of the study. It can be speculated that MG 4, MG 4.5, and MG 5 based diets might have improved palatability, leading to higher FI, and that MG 4.5 and MG 5 may enhance feed efficiency due to better nutrient digestibility. However, further investigation is warranted to confirm these hypotheses.
While this study identified key differences in AA composition and digestibility among soybean varieties, several limitations should be noted. Other nutritional components, such as carbohydrates, and anti-nutritional factors (e.g., trypsin inhibitors, saponins, and oligosaccharides) were not evaluated. These factors are known to affect the nutritional value and digestibility of soybean products (Frikha et al., 2012). De Coca-Sinova et al. (2008) and Frikha et al. (2012) reported that CP content and trypsin inhibitor activity are negatively correlated with lysine digestibility in broilers.
Overall, the findings from both the in vitro and in-vivo evaluation showed that the maturity groups 4.5 and 5 to have improved protein and amino acid digestibility suggesting later maturing soybeans may offer enhanced nutritional values for broiler dietary formulations. Future study is required to understand the mechanism of their higher AA digestibility. This study had limited replication for comparing AA digestibility, which should be considered in future research that might give more consistent results between in-vitro and in-vivo. Future research should include a comprehensive evaluation of anti-nutritional components and their impact on nutrient utilization. Furthermore, standardizing SBM processing methods and conducting floor pen-based bird studies may help identify subtle differences in digestibility and bird performance. Ultimately, identifying soybean varieties and MGs that have better digestibility coefficients could support the formulation of cost-effective and nutritionally efficient broiler diets.
CRediT authorship contribution statement
Alexis McDade: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. Md Raihanul Hoque: Writing – original draft, Visualization, Methodology, Formal analysis, Data curation, Conceptualization. Virginia R. Sykes: Resources, Project administration, Data curation. Ali Taheri: Supervision, Resources, Investigation. Samuel Nahashon: Validation, Resources, Project administration. Pramir Maharjan: Writing – review & editing, Methodology, Investigation, Conceptualization.
Disclosures
The authors declare no conflict of interest about this manuscript.
Acknowledgement
We would like to acknowledge Tennessee Soybean Promotion Board for funding this work, and Cobb Vantress, Inc. for providing broiler chicks to conduct the bird work. The author would also like to thank Bayer Crop Science and Ag Nutrient Solutions for providing seeds to do this work.
Footnotes
Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.psj.2026.106593.
Appendix. Supplementary materials
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