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

• Published in: Applied Animal Science 2022-02, Vol.38 (1), p.13-21
• Main Authors: Martinez, Javier J., Löest, Clint A., McCuistion, Kimberly C., Wester, David B., Bell, Natasha L.
• Format: Article
• Language: English
• Subjects: efficiency; grazing; ionophore; ruminant; supplementation
• ISSN: 2590-2865; 2590-2865
• DOI: 10.15232/aas.2021-02219

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. 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.). 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. Although monensin altered ruminal VFA profiles, providing monensin to cows consuming a low-quality-forage diet provided no benefits in forage intake or digestion.