Effects of monensin and protein supplementation on intake, digestion, and ruminal fermentation in beef cattle consuming low-quality forage

Abstract

Objective: The objective of this study was to evaluate the effects of monensin and protein supplementation and their interaction on intake, apparent digestion, and ruminal fermentation variables in cattle consuming low-quality forage. Materials and Methods: Four ruminally cannulated cows (637 ± 24 kg of BW) were used in a 4 × 4 Latin square design. Treatments were arranged as a 2 × 2 factorial: (1) monensin (0 or 200 mg∙cow−1∙d−1) and (2) protein (0 or 0.64 kg∙cow−1∙d−1 CP). Day 1 through 4 of each period, animals were fed only low-quality forage, d 5 through 14 allowed for treatment adaptation, and d 15 through 20 were for sample collection. Data were analyzed using the MIXED procedure of SAS 9.4 (SAS Institute Inc.). Results and Discussion: Neither a monensin × protein interaction nor a monensin effect (P ≥ 0.30) was observed for any intake or digestion variable measured. In contrast, protein treatment increased (P < 0.01) all measures of intake. Protein increased (P < 0.01) OM digestibility, total digestible OM intake, and total digestible NDF intake but had no effect (P = 0.13) on NDF digestibility. A monensin × protein interaction (P = 0.33) or monensin effect (P = 0.34) were not observed for total VFA concentration, but protein increased (P < 0.01) total VFA concentration. A tendency for monensin × protein interaction was observed for the acetate:propionate ratio (P = 0.06) and molar percentage of propionate. Monensin increased (P < 0.01) molar percentage of propionate but had no effect (P = 0.21) on acetate. Implications and Applications: Although monensin altered ruminal VFA profiles, providing monensin to cows consuming a low-quality-forage diet provided no benefits in forage intake or digestion.