Effect of monensin or ruminal fermentation, forage intake and weight gains of wheat pasture stocker cattle

The effects of monensin or ruminal fermentation, forage intake and weight gains of stocker cattle grazed on wheat pasture were studied. In the first of two ruminal fermentation studies, ruminal fluid pH was increased and total volatile fatty acid (VFA) concentrations at 4 (p less than .01) and 24 hr postfeeding were decreased in steers fed 200 mg monensin/day. However, no such changes in ruminal fluid pH and total VFA concentrations in monensin-fed steers were observed in trial 2. The ruminal fluid acetic to propionic acid ratio of steers that received monensin was decreased (P less than 0.5) by about 40 and 20% of trials 1 and 2, respectively. Results of two forage intake trials, in which steers received 0 or 200 mg monensin daily, were not consistent, precluding conclusions about the effect of monensin, per se, on stocking rate adjustments when the additive is used in wheat pasture stocker programs. In each of two growth trials, conducted over 2 years, about 125 heifers per year were divided into three groups: one group grazed wheat pasture and received no supplement, and the other two grazed wheat pasture and were fed a pelleted supplement that contained 0 or 100 mg monesin. Daily gains of heifers fed monensin were .08 kg greater (p less than .01) than those fed supplement without monensin. The data indicate that monesin does have potential for use in wheat pasture stocker programs.