Influence of monensin fed with a starch-based energy supplement on forage digestibility and intake by range cows during drought

Management strategies that maintain livestock performance while reducing intake in times of low forage availability, such as drought, are valuable. The hypotheses of this experiment were that a grain-based supplement would decrease forage intake and digestibility, whereas a grain-based supplement plus monensin would decrease forage intake and increase forage digestibility. Crossbred cows (n=36) grazing native range pasture during the late summer were used in a randomized complete block design for 2yr (average forage quality for yr 1=8.7% CP, 77% NDF, 47% ADF; for yr 2=8.0% CP, 76% NDF, 45% ADF). Treatments were control (no supplement; NS), cracked corn (S; 0.91kg/cow per day, as-fed basis), and S with monensin added at 385mg/kg of corn (SM). Diet samples were collected from 6 ruminally cannulated cows to calculate digestibility. Cows were dosed with Cr2O3 boluses to determine fecal output, OM intake, and digestible OM intake during 2 sampling periods each year. Forage intake and digestible OM intake as percentages of BW were greater (P0.05) in yr 2. Starch-based supplement alone reduced OM and NDF digestibility in period 1 of both years compared with NS or SM treatments (P