Rusitec (Czerkawski and Breckenndge, 1977) lias been widely used to study factors which affect rumen fermentation such as monensin, monensin-propionate, abierixin, calcimycin and Aspergillus oryzae (Bogaert et al., 1990; Newbold et al., 1993). Monensin is a grain-positive ionophore which modifies rumen fermentation. The objective of the current study was to determine the effect of monensin on molar proportions of volatile fatty acid (VFA) produced from diets which varied in foragexoncentrate ratio.
Four Rusitec vessels (800 ml) were used in an extended Latin Square design with 2 blocks, 2 treatments and 3 periods, each lasting 14 days. To initiate each period, inocula was recovered from the same lactating Holstein-Friesian cow (∽650 kg). All vessels received 15 g DM/day of a complete diet which contained maize silage, grass silage, NaOH treated wheat grain and a protein supplement in three foragexoncentrate ratios; 25:75 (L), 50:50 (M) and 75:25 (H).