Effects of cyclic monensin feeding on ruminally cannulated beef steers consuming low-quality forage

Effects of cyclically feeding monensin to ruminally cannulated steers (12 Bos taurus; 260 kg BW) consuming low-quality forage (LQF; 4.9%CP) were evaluated. Steers were randomly assigned to one of three treatments: 1) CON (0 mg·hd−1·d−1 monensin; Rumensin® 90, Elanco Animal Health, Greenfield, IN), 2) MON (200 mg·hd−1·d−1 monensin) or 3) CYC (200 mg·hd−1·d−1 monensin for 14 d and 0 mg·hd−1·d−1 monensin for subsequent 14 d). Dried distillers’ grains with solubles (1 kg·hd−1·d−1) were fed for monensin inclusion. Each of four periods was 28 days in length. Hay and ort samples were collected d 10-13 for intake determination. Rumen fluid was collected with a suction strainer 0, 2, 4, 8, and 12 h after feeding on d 14 for pH and VFA (volatile fatty acid) analysis. Data were analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC). A period × treatment interaction was not observed for any measure of digestion (DMD, OMD, NDFD; P ≥ 0.39), intake (DMI, OMI, NDFI; P ≥ 0.86) or pH (P = 0.15). An hour effect was observed for pH during all four periods (P ≤ 0.01). A period × treatment interaction (P < 0.01) was observed for acetate, propionate, and A:P when all periods were analyzed together. An hour effect was observed in all ruminal fermentation parameters (acetate, propionate, A:P ratio, total VFA; P ≤ 0.01). No treatment effects for any ruminal fermentation parameters or interactions were observed by period 4 (P ≥ 0.15). Only an hour effect was observed during period 4 for all ruminal fermentation parameters (P ≤ 0.03)