Impacts of replacing corn silage with soyhulls as a roughage source on intake and ruminal fermentation in steers fed high-concentrate diets

Authors: Neville, Bryan; PICKINPAUGH, W - North Dakota State University; MOORE, R - North Dakota State University; SWANSON, K - North Dakota State University; CATON, J - North Dakota State University

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 8/3/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Six ruminally cannulated steers (475.0 ± 49.6 kg) were used in a 6 × 3 incomplete Latin square design (6 treatments and 3 periods), to evaluate the impacts replacement of corn silage with soyhulls as roughage in high-concentrate finishing diets containing 30% modified distillers grains with solubles. Treatments were based on increasing dietary inclusion of soyhulls and consisted of: 1) Control (0), roughage supplied by dietary inclusion of 20% corn silage (DM basis), 2) 50% replacement of corn silage with soyhulls (50), 3) 100% replacement of corn silage with soyhulls (100), and the same three treatments repeated with 3% added cereal straw (DM basis) replacing corn in the diet. Each collection period consisted of 7 days of adaptation followed by 7 days of collection. Fecal output was calculated using chromic oxide as an external marker. Ruminal fluid was collected for determination of ruminal pH, volatile fatty acid concentrations, and fluid kinetics. Dry matter intake (DMI) tended to decrease (P = 0.06) with increasing soyhull inclusion but was not affected by the addition of straw to the diet (P = 0.29). Total tract digestibility of dry matter, protein, neutral detergent fiber and acid detergent fiber were not affected by soyhull inclusion or added straw (P >/= 0.31). Ruminal pH did not differ (P = 0.61) with increasing soyhull inclusion but increased with the addition of straw (P < 0.01; 5.9 vs. 6.1 for no straw and straw, respectively). Molar proportions of acetate and butyrate decreased while propionate increased with increased soyhull inclusion (P < 0.01). Ruminal fluid kinetics were unaffected by treatment (P >/= 0.31). The results of this study appear to indicate that substituting soyhulls for corn silage as a roughage source does not affect ruminal pH and that added straw will increase ruminal pH. However, DMI decreased by 1.9 and 2.3 kg/d when comparing the 0 and 100 treatments for the added straw and no straw treatments, respectively. Decreases in DMI of this magnitude would likely decrease feedlot cattle performance and underscores the need for additional research prior to recommending this practice to cattle feeders.