RESPONSES IN CILIATED PROTOZOA AND RUMEN FERMENTATION IN SHEEP SUPPLEMENTED WITH BARLEY PLUS VIRGINIAMYCIN

An experiment was conducted to determine the changes in the population of ciliate protozoa and the pattern of rumen fermentation in sheep fe d 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 virginiamyc in (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 plu s 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 wa s fed). In sheep supplemented with barley the population density of ci liate protozoa was increased (P < 0.01) from day 3 of the 5 day introd uction to grain (approximately 170 x 10(4) 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 pop ulation density of ciliate protozoa was increased significantly (P < 0 .01) only at days 5 and 6 of the experiment (approximately 100 x 10(4) protozoa/ml at day 5). Sheep supplemented with barley plus virginiamy cin at day 5 had a higher concentration of L-lactate (P < 0.05) at 6 a nd 12 h and propionate (P < 0.05) at 6, 9, 12 and 24 h than sheep supp lemented with barley alone. It was concluded that virginiamycin was in hibitory to protozoa during the introduction to grain, and L-lactate a ccumulation in the rumen of sheep supplemented with barley plus virgin iamycin may be a result of altered fermentation associated with reduce d numbers of protozoa.