Effects of orally administered ionophore antibiotic (monensin) on the rumen protozoa and their activities in Sheep

The aim of this this study was to investigate the changes of the biophysical characteristics and biochemical values of the rumen liquor, as well as the alterations of the total and differential counts of rumen protozoa associated with oral administration of monensin in sheep. Ten native breed sheep, 2–2.5 years old, weighing between 30–45 kg body weight (BW) were used. All animals were subjected to detailed physical examination for 1 week before the start of the trial provided with regular feeding regimen. The experimental animals were subjected to oral administration of monensin at a dose rate of 0.66 mg/kg BW for 7 successive days. Rumen fluid samples were obtained from each animal in three occasions, once before treatment, 48 hours and 7 days after treatment. The ruminal fluid samples were subjected to physical and microscopical examinations in addition to the biochemical analysis. The results revealed that, oral administration of monensin resulted in deleterious effects on the rumen microbial ecosystem. Such disturbances included highly significant reduction in the total protozoal count (396.3± 26.2, 353.25±16.05x10³/ml), Isotrichs (10.65±1.3, 10.65±1.2 x10³/ml), Dasytrichs (1.5±0.6, 1.2±0.4 x10³/ml) and entodiniomorphs particularly, genera Entodinium (372.20±21.9, 333.45±17.05 x10³/ml), polyplastron (6.99±1.8, 3.45±1.05 x10³/ml) and Ophryoscolex (4.50±0.9, 4.2 ±0.5 x10³/ml) 48 hours and 7 days after treatment, respectively. Moreover, significant decrease in the mean values of ammonia (82.0±3.4, 78.2±2.4), rumen pH (6.05±0.17, 5.8±0.05), delayed cellulose digestion (48.2±2.6, 16.2±2.03 hrs) and improper redox-potential activity (8.4 ±0.40, 16.2 ±0.55 min) were also evident 48 hours and 7 days after treatment, respectively. Lastly, there was a significant increase in the mean values of propionate concentration (23.5±1.0, 25.5±1.0 mmol/l) with significant decrease in acetate (52.5±0.9, 46.2±1.1 mmol/l) and butyrate concentrations (5.9±1.2, 5.21±0.2 mmol/l) as well as total volatile fatty acids concentration (81.9±1.4, 76.9±1.6 mmol/l) in the rumen liquor of monensin-treated sheep 48 hours and 7 days after treatment if compared with their control values.