| Abstrakt: |
Three experiments utilizing three Holstein steers (235 and 299 kg avg body weight for Exp. 1 and 2, respectively) were conducted to evaluate the effects of decoquinate, a synthetic coccidiostat, on ruminal fermentation, diet digestibility and performance of steers fed a finishing diet containing monensin and tylosin. Experiment 1 utilized a 70% forage diet, whereas Exp. 2 utilized a 20% forage diet. Each experiment was a 3 × 3 Latin-square design with treatments being 0, .5 and 5 mg decoquinate/kg body weight. Ruminal fermentation characteristics, water kinetics and blood constituents were measured on d 11 of each period, and zero-time volatile fatty acid (VFA) production was measured at 3 and 6 h post-feeding on d 12 to 14. No changes were seen in plasma glucose or L-lactate, ruminal pH, NH3-N or ruminal L-lactate for either experiment. Dry matter digestibility was depressed (P<.05) at the .5- and 5-mg levels of decoquinate in Exp. 1, but dry matter digestibility was not affected in Exp. 2. No changes were seen in ruminal volume, outflow or total VFA concentration for either experiment. Molar proportions of VFA were not affected in Exp. 1, but the proportions of isobutyrate and butyrate decreased (P<.05) at the 5-mg level of decoquinate in Exp. 2. Volatile fatty acid production was not changed in Exp. 1, but butyrate production was decreased (P<.05) at the 5-mg level in Exp. 2. Experiment 3 involved 135 crossbred steers (259 kg avg initial wt), which were stratified by weight into 12 pens. Treatments were control (no additive), decoquinate .5 mg/kg body weight for the entire experiment, decoquinate for 28 d followed by monensin and tylosin (25 and 10 g/t of feed) for the remainder of the experiment and monensin and tylosin for the entire experiment (147 d). Diets were fed once daily, and were comprised of 80% grain, 10% supplement and 10% forage. Decoquinate did not affect steer performance. Monensin- and tylosin-fed steers tended (P>.05) to be more efficient (5.4%), but overall there was no difference in performance. Results of these experiments indicate that improvements in steer performance from the addition of decoquinate are probably due to its role as a coccidiostat and not due to any modification in diet utilization or ruminal fermentation characteristics. |
