EFFECTS OF ARDACIN SUPPLEMENTATION ON RUMEN FERMENTATION AND PROTEIN DEGRADABILITY IN STEERS

Ardacin is an antibacterial glycopeptide with ruminal activity, The ob jective of this study was to determine its effects on rumen fermentati on, soyabean meal degradability and concentrations of selected metabol ites in plasma of steers, Six rumen fistulated steers (initial bodywei ght 622, S.D. 99.8 kg) were used in a replicated 3 (0, 0.5 or 1.0 mg a rdacin kg(-1) bodyweight) by 3 (21 day periods) Latin square experimen t and fed a diet of 450 g concentrate and 550 g grass silage kg(-1) dr y matter (DM) at a daily allowance of 13.5 g DM kg(-1) bodyweight, Die tary inclusion of ardacin did not affect mean rumen fluid pH or concen trations of ammonia or total volatile fatty acids in rumen fluid. Diet ary inclusion of ardacin increased (linear, P <0.05) the molar proport ion of propionate, decreased (linear, P <0.001) the molar proportion o f acetate and decreased (linear, P <0.01) the acetate: propionate rati o in rumen fluid. At 8 h after the first feed, the butyrate proportion was higher (P <0.05) in animals fed 1.0 mg ardacin kg(-1) bodyweight than in the other treatments. When compared to animals not offered ard acin, the molar proportion of valerate was lower(P <0.05) in animals f ed 0.5 mg kg(-1) bodyweight and tended to be higher (P <0.1) in those fed 1.0 mg kg(-1) bodyweight. The rate of disappearance of soyabean me al from nylon bags incubated in the rumen was lower (linear, P <0.05) in steers fed ardacin. Plasma concentrations of glucose, non-esterifie d fatty acids and l-lactic acid were unaffected by inclusion of ardaci n in the diet. Plasma urea concentration tended to be increased in the 8-12 h period after the first feed. It is concluded that ardacin alte red rumen fermentation in a dose-dependant manner in a direction sugge stive of improved growth and/or feed conversion efficiency and may inc rease the quantity of dietary protein supplied to the small intestine.