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Determining amino acid digestibility of soybean meal from different South Carolina soybean varieties when fed to broilers

Dunmire, K., M. Braun, C. Evans, B. Fallen, C. Stark and C. Paulk

At hatch, 240 Ross 308 male broilers were placed in battery cages for a 15-d study to evaluate amino acid digestibility of soybean meal from specialty variety soybeans grown in South Carolina. There were 10 replicates per treatment and 6 broilers per cage. Broilers were given a common corn soybean meal-based diet from d 0 to 9. On d 9, broilers were weighed, and cages were allotted to 1 of 4 dietary treatments within location block. Soybean meal (SBM) sources consisted of a conventionally processed control SBM (45.4% CP; CON), and soybeans sourced from the same region, processed using solvent extraction at Texas A&M University (49.8% CP; PCON). Two additional soybean varieties were solvent extracted at Texas A&M and resulting SBM (53.1% CP; 53SBM and 57.4% CP; 57SBM) used in this experiment. Assay diets were dextrose and SBM-based and consisted of 1 of 4 soybean meal sources formulated to supply 20% dietary CP with titanium dioxide as an indigestible marker. On d 15, broilers were euthanized by CO2 inhalation and ileal samples were collected to determine apparent ileal digestibility (AID) of amino acids (AA). Data were analyzed using the GLIMMIX procedure in SAS 9.4, with pen as the experimental unit, pen location as the blocking factor and adjusted using Tukey-Kramer multiple comparisons. Broilers fed CON and 57SBM had increased (P < 0.003) AID of total AA (77.3 and 81.5% vs. 71.6 and 69.0%), arginine (85.2 and 88.5% vs. 80.5 and 79.6%), histidine (80.2 and 83.1% vs. 74.1 and 72.2%), lysine (79.7 and 82.2% vs. 71.4 and 69.2%), threonine (77.4 and 80.0% vs. 69.8 and 66.2%), and tryptophan (75.7 and 82.5 vs. 73.8 and 72.6%) compared to those fed PCON and 53SBM. The AID of isoleucine and phenylalanine increased (P < 0.001) in broilers fed 57SBM (81.6 and 83.2%) compared to CON (76.9 and 77.7%) and 53SBM (73.5 and 72.5%), where PCON (72.8 and 74.7%) was intermediate to CON and 53SBM. Broilers fed 57SBM had increased (P < 0.001) AID of leucine (82.1%) compared to all other sources. The AID of methionine increased (P = 0.007) in broilers fed CON (80.2%) and 57SBM (81.3%) compared to 53SBM (70.9%), where there was no evidence for differences between those fed PCON (73.8%) and all other sources. Broilers fed CON (74.2%) and 57SBM (79.1%) had increased (P < 0.001) digestibility of valine compared to PCON (69.7%) and 53SBM (66.3%) with no evidence for difference between those fed CON and PCON.

In conclusion, broilers fed commercially processed soybean meal had improved AA digestibility compared to those fed experimentally processed soybeans from a similar region. The high CP (57% CP) SBM variety had increased AA digestibility compared to the PCON and 53SBM.