Effect of tween 80 and salinomycin on ruminal fermentation and nutrient digestion in steers fed a diet containing 70% barley

Ten Jersey steers (484 ± 55 kg) were fed a basal diet of 70% rolled barley grain and 30% alfalfa silage [dry matter (DM) basis] with or without additives, in a replicated 5 × 5 Latin square experiment. Treatments (additives per kilogram dietary DM) were: C, no additives (control); T, Tween 80 (2 g kg^-1); SH, salinomycin (13 mg kg^-1); TSM, Tween 80 (2 g kg^-1) plus salinomycin (6.5 mg kg^-1); and TSL, Tween 80 (2 g kg^-1) plus salinomycin (3.25 mg kg^-1). Ruminal pH, concentrations of ammonia, total free amino acids, reducing sugars and total volatile fatty acids (VFA), and fluid phase viscosity were unaffected (P > 0.05) by treatment. Ruminal carboxymethylcellulase, xylanase and amylase activities, numbers of protozoa, and outflow rates of the liquid and solid phases of ruminai contents did not differ (P > 0.05) among treatments. Ruminal lactic acid bacteria populations tended (P < 0.1) to be smaller with SH compared with C, but counts were unaffected (P > 0.05) by T, TSL and TSM. Partitioning of ruminai digesta and microbial protein flow were similar (P > 0.05) among treatments. Compared with C, the ruminai rate of degradation (in situ) of alfalfa DM tended to be higher (P < 0.10) with SH, and the rate of barley grain DM degradation was higher (P < 0.05) with T. Intake and apparent digestibilities of DM, neutral detergent fibre (NDF), acid detergent fibre (ADF) and crude protein were unaffected (P > 0.05) by treatment, as were blood glucose and urea levels. Tween 80 and salinomycin did not affect ruminai fermentation or nutrient digestibility in steers fed a barley grain/alfalfa silage diet.