The effect of corn silage harvest DM and rumen undegradable protein supplementation in silage growing diets growing beef cattle

Abstract Text: A 78-d growing study was conducted utilizing 60 crossbred steers (initial BW = 271; SD = 32 kg) to evaluate the effects of harvesting drier corn silage and response to rumen undegradable protein (RUP) supplementation.  Previous data suggests DM yield and starch (i. e., grain) content may be increased if silage harvest is delayed.  Treatments were arranged as a 2 × 5 factorial design. Factors included harvested corn silage DM (37 or 43%) and supplemental RUP inclusion (0.0, 2.5, 5, 7.5, or 10% of diet DM). Supplemental RUP was a blend of corn gluten meal and non-enzymatically browned soybean meal (Soypass). Steers were individually fed using Calan gates and were limit fed a common diet at 2% of BW for 5 d followed by weighing 3 consecutive d at the beginning and end of the experiment for accurate BW collection. Steers were stratified by initial BW using the average of d -1 and d 0 BW, and assigned randomly to treatment with 5 to 8 steers per supplemental RUP inclusion within each silage DM (n = 8 for 0% RUP; n = 5 for 2.5% and 5 % RUP; n = 6 for 7.5% and 10.0% RUP treatments).  Due to a limited number of bunks, a greater number of animals were used at 0%, 7.5% and 10% supplemental RUP inclusion as we hypothesized metabolizable protein needs would be met at 7.5%. No linear (P ≥ 0.33) or quadratic (P ≥ 0.36) interactions were observed between corn silage DM and supplemental RUP inclusion (P ≥ 0.22) for growing performance. As DM of corn silage increased from 37 to 43%, there was a significant decrease (P = 0.04) in ending BW due to reduced (P = 0.01) ADG. Steers fed 37% DM silage had greater (P < 0.01) G:F compared to steers fed 43% DM silage. Increasing supplemental RUP in the diet increased (P ≤ 0.05) ending BW, DMI, and ADG linearly as supplemental RUP increased from 0 to 10%.  With both an increase in DMI and ADG, G:F increased (P < 0.01) linearly as supplemental RUP inclusion increased.  Feeding silage in growing diets at 88% inclusion shows that 37% DM silage results in greater ADG and G:F compared to 43% corn silage.  The addition of RUP to silage-based, growing diets will improve performance by supplying more metabolizable protein and suggests RUP of corn silage is limiting.

Keywords: Corn silage, Dry matter, Rumen undegradable protein