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 X 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 less than .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 less than .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 less than .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.(ABSTRACT TRUNCATED AT 250 WORDS)