Evaluation of several potential bioactive agents for reducing protozoal activity in vitro

The effects of 14 bioactive agents on ruminal fermentation and protozoal activity were investigated in vitro as potential feed additives to improve feed efficiency. Agents studied were: lecithin, herring meal, canola oil, coconut oil, linseed oil, palm oil, and soybean oil, with each oil at final concentrations of 0.5, 1.0 and 2.0%; the saponin-containing plants Yucca schidigera (yucca) and Quillaja saponaria Molina (quillaja), tannic acid, and bentonite, each at 0.1, 0.2. and 0.4%; the surfactant Tween 80 (at 0.05, 0.1, and 0.2%); and the ionophores monensin (at 2.5, 5.0, and 10 mg/l) and salinomycin (at 1.25, 2.5, and 5.0 mg/l). Duplicate 4 h incubations each included controls (no additives) and ¹⁵N labeled casein as a N tracer. Yucca, tannic acid and both ionophores decreased (P < 0.05) NH₃ concentrations. Total free amino acids (TFAA) were decreased (P < 0.05) by yucca and by bentonite, but were increased (P < 0.05) by fish meal, monensin and salinomycin. Tannic acid and bentonite reduced (P < 0.05) total VFA concentrations, and tannic acid reduced (P < 0.05) the acetate:propionate (A:P) ratio. Bentonite, tannic acid, palm oil, quillaja and salinomycin reduced (P < 0.05) carboxymethylcellulase (CMCase), xylanase, and amylase activities, whereas monensin, lecithin, Tween 80, yucca, and the feed oils (except coconut) decreased (P < 0.05) amylase activity only. Protozoal populations, which comprised 84% Entodinium spp., decreased (P < 0.05) with tannic acid, lecithin and quillaja. Tannic acid, fish meal, and the ionophores reduced (P < 0.05) the rate of protozoal engulfment of bacteria. Fish meal and salinomycin, and the higher concentrations of quillaja and Tween 80 depressed (P < 0.05) incorporation of ¹⁵N from casein into bacterial cells. Only lecithin effectively reduced protozoal numbers, by 27%, without impeding the extent of ¹⁵N incorporation into bacteria.