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Ardacin is an antibacterial glycopeptide with ruminal activity. The objective of this study was to determine its effects on rumen fermentation, soyabean meal degradability and concentrations of selected metabolites in plasma of steers. Six rumen fistulated steers (initial bodyweight 622, S.D. 99.8 kg) were used in a replicated 3 (0, 0.5 or 1.0 mg ardacin kg−1 bodyweight) by 3 (21 day periods) Latin square experiment and fed a diet of 450 g concentrate and 550 g grass silage kg−1 dry matter (DM) at a daily allowance of 13.5 g DM kg−1 bodyweight. Dietary inclusion of ardacin did not affect mean rumen fluid pH or concentrations of ammonia or total volatile fatty acids in rumen fluid. Dietary inclusion of ardacin increased (linear, P < 0.05) the molar proportion of propionate, decreased (linear P < 0.001) the molar proportion of acetate and decreased (linear, P < 0.01) the acetate: propionate ratio 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 ardacin, the molar proportion of valerate was lower (P < 0.05) in animals fed 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 meal from nylon bags incubated in the rumen was lower (linear, P < 0.05) in steers fed ardacin. Plasma concentrations of glucose, non-esterified fatty acids and 1-lactic acid were unaffected by inclusion of ardacin 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 altered rumen fermentation in a dose-dependent manner in a direction suggestive of improved growth and/or feed conversion efficiency and may increase the quantity of dietary protein supplied to the small intestine. |
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