Abstract:
An experiment was conducted to determine the changes in the population of ciliate protozoa and the pattern of rumen fermentation in sheep fed a supplement of barley grain on its own or containing virginiamycin. There were three treatment groups with a total of 25 sheep housed in individual pens. All animals were fed chaffed wheaten hay to a maximum of 1.4 kg head-1 day-1. One group received no grain supplement (n = 5), one barley grain (n = 10) and the third barley plus virginiamycin (40 g/t grain; n = 10). The amount of grain was gradually increased over a period of 5 days to a maximum of 700 g of barley or barley plus virginiamycin on day 5. Grain (700 g/head) was then fed twice weekly for a further 18 days. Samples of rumen fluid were taken on days 1, 2, 3, 5*, 6, 9*, 12*, 23* and 24 (* signifies days when 700 g barley was fed). In sheep supplemented with barley the population density of ciliate protozoa was increased (P < 0.01) from day 3 of the 5 day introduction to grain (approximately 170x104 protozoa/mL at day 5), but the increase was not sustained when grain was fed at intervals of 3 or 4 days. In sheep supplemented with barley plus virginiamycin, the population density of ciliate protozoa was increased significantly (P < 0.01) only at days 5 and 6 of the experiment (approximately 100x l04 protozoa/mL at day 5). Sheep supplemented with barley plus virginiamycin at day 5 had a higher concentration of L-lactate (P < 0.05) at 6 and 12 h and propionate (P < 0.05) at 6, 9, 12 and 24 h than sheep supplemented with barley alone. It was concluded that virginiamycin was inhibitory to protozoa during the introduction to grain, and L-lactate accumulation in the rumen of sheep supplemented with barley plus virginiamycin may be a result of altered fermentation associated with reduced numbers of protozoa.