Effects of Salinomycin Feeding on Feed Conversion and Ruminal Traits of Streers

Eight Hereford steers weighing 295 kg initially were used for a 102-day experiment consisting of three experimental periods: a 30-day pre-treatment period (I), a 36-day salinomycin(SL) treartment period (II) and a 36-day post-treatment period (III) (Fig. 1). SL, a polyether antibiotic produced by Streptomyces albus, was blended with the concentrate (Table 1) and fed to steers during the peiod II at the level of 100 mg per day per head. Ruminal samples were obtained 3hr after feeding with a catheter at the indicated days in Fig. 1. Daily gain and feed conversion of steers in period II were much better than those in the other two periods (Table 3). Ruminal concentrations of acetate and butyrate decreased and those of propionate increased with SL treatment (Table 4), Corresponding significant decrease and inuease in molar proportions of these voiatile fatty acids (VFA) were recorded (Table 4). Ruminal total VFA, pH, viscosity and in vitro gas production rates were not consistently affected by feeding SL (Table 4 and Fig. 2). Ruminal ammonia nitrogen decreased significantly with SL treatment (Table 4). Total counts of rumen protozoa decreased by SL to nearly one half of the pre-treatment period (Fig. 3), but generic compositions of ciliates were similar thoughout the experiment: entodinium 80-99%, diplodiniun 2-7% and holotricha 5-10% (Fig.4). Total counts of ruminal bacteria significantly increased by feeding SL and tended to decrease by the removal of SL from the diet (Fig. 5). Both Gram negative (group no. 1) and positive cocci (group no. 4) increased, and two types of rods, Gram negative (group no. 13) and positive (group no. 19), decreased with SL treatment (Fig. 5 and Table 2)