Impacts of added roughage on growth performance, digestibility, ruminal fermentation, and ruminal pH of feedlot steers fed wheat-based feedlot diets containing 30% modified distillers grains with solubles

Authors: PICKINPAUGH, WAYDE - North Dakota State University; Neville, Bryan; MOORE, REBECCA - North Dakota State University; CATON, JOEL - North Dakota State University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2022
Publication Date: 5/12/2022
Citation: Pickinpaugh, W.J., Neville, B.W., Moore, R.L., Caton, J.S. 2022. Impacts of added roughage on growth performance, digestibility, ruminal fermentation, and ruminal pH of feedlot steers fed wheat-based feedlot diets containing 30% modified distillers grains with solubles. Translational Animal Science. 6(2). Article txac051. https://doi.org/10.1093/tas/txac051.
DOI: https://doi.org/10.1093/tas/txac051

Interpretive Summary: Wheat is an alternative grain source that can be used in feedlot cattle diets; however, the rapid rate of fermentation of wheat can increase risk of acidosis. To reduce the risk of acidosis with rapidly fermenting grains, roughage can be added to the diet to assist in increasing rumen pH. However, when fed with low-starch energy sources like modified distillers grains with solubles the impacts of roughage inclusion on ruminal fermentation and pH, as well as steer performance are less well understood. The objective of this study was to evaluate the impacts of including additional roughage on feedlot performance, nutrient digestibility, ruminal fermentation, and ruminal pH of steers fed wheat-based feedlot rations including 30% modified distillers grains with solubles. Our data appear to indicate that increasing roughage inclusion from 10 to 16% of dietary DM in wheat-based diets including modified distillers grains with solubles did not impact feedlot performance, had minimal impacts on organic matter digestibility, and increased ruminal pH. The lack of subacute acidosis, as indicated by rumen fluid pH, in our digestibility study and our feedlot performance data indicate that feedlot producers feeding combinations of modified distillers grains with solubles and wheat may not need to increase roughage inclusion above 10% (DM basis) under similar management conditions to the present study.

Technical Abstract: Two experiments were conducted to evaluate the inclusion rate roughage in wheat-based diets containing modified distillers grains with solubles (MDGS) on feedlot performance (Feedlot Experiment), as well as digestibility, ruminal pH, and ruminal fermentation characteristics (Digestibility Experiment). The feedlot experiment utilized 72 Angus steers (392 ± 46.3 kg initial body weight) which were randomly assigned to 1 of 12 pens, 3 pens per treatment, to evaluate feedlot performance and carcass characteristics. Dietary treatments were 1) control; 10% roughage, 2) 12% roughage, 3) 14% roughage, and 4) 16% roughage. The digestibility experiment used four ruminally and duodenally cannulated steers (393 ± 33.0 kg) in a 4 × 4 Latin Square with either 10%, 12%, 14%, or 16% roughage as in the feedlot experiment. However, dietary roughage source was different between these two experiments and included a combination of grass hay and wheat straw (Feedlot Experiment), and corn silage (Digestibility Experiment). All data were analyzed with the Mixed Procedures of SAS. Feed intake was recorded, with duodenal and fecal output calculated using chromic oxide. Ruminal pH and fermentation were assessed. Growth performance and most carcass characteristics were not affected by increasing roughage (P = 0.11). Marbling tended to decrease linearly (P = 0.10) with increasing roughage inclusion. Increasing dietary roughage content had no effect on organic matter intake (P = 0.60) in the digestibility experiment. Intake, duodenal flow, and digestibility of neutral detergent fiber and acid detergent fiber were not affected by treatment (P = 0.16). Ruminal pH increased linearly (P < 0.01) as rate of roughage inclusion increased. Ruminal concentrations of acetate and butyrate increased, and propionate decreased in a linear fashion (P < 0.01) thereby increasing (P < 0.01) acetate and butyrate to propionate ratio with increasing dietary roughage. Our data indicate that increasing roughage inclusion in wheat-based diets including 30% MDGS increased ruminal pH and shifted ruminal fermentation patterns. Additionally, increasing roughage inclusion did not affect feedlot performance in steers fed wheat at 36 to 42% of dietary DM in combination with 30% MDGS.