One hundred twenty individually fed steers (initial BW 283 kg) were utilized in an 84-d growing trial to evaluate effects of increased metabolizable lysine from non-enzymatically browned soybean meal (SoyPass) in grass hay based diets containing wet distillers grains plus solubles (WDGS).
Treatments were arranged as a 2 × 3 factorial design with two levels of WDGS (20% or 35% of DM) and three levels of supplemental SoyPass replacing 0%, 30%, or 60% of WDGS. The statistical model included animal as the experimental unit and level of WDGS and SoyPass substitution were included as fixed effects. Covariate regression was used to test for linear and quadratic interactions between WDGS and SoyPass substitution. No interactions were detected for ADG between SoyPass supplementation and level of WDGS in the diet (P = 0.76). Additionally, SoyPass inclusion had no effect on ADG (P = 0.49).
However, ADG was increased for steers consuming the 35% WDGS diet compared to steers offered the 20% WDGS diet (1.13 vs. 0.86 kg/d, respectively; P < 0.01). A SoyPass × WDGS interaction was detected for DMI (P = 0.01). As SoyPass replaced WDGS in the 35% diet, DMI increased linearly from 8.10 to 8.93 kg/d (P = 0.01). In the 20% WDGS diet, DMI decreased as SoyPass replaced 60% of the WDGS compared to 30% (7.68 vs. 8.36, P = 0.02).
Therefore, G:F decreased linearly (P = 0.01) as SoyPass replaced WDGS in the 35% treatment and increased quadratically (P = 0.02) for the 20% WDGS treatment. Furthermore, BUN increased linearly as SoyPass replaced WDGS in the 20% diet (P = 0.01) but was not affected by SoyPass substitution in the 35% diet.
Overall, results indicate forage-based growing diets formulated with low-levels of WDGS (< 20%) may be deficient in metabolizable lysine, which could be supplied with SoyPass.