Oocyst discharge, rumen metabolism and performance of early weaned lambs with naturally occurring coccidiosis fed monensin.

Ninety-six 9.5 kg early-weaned lambs with naturally occurring coccidiosis were fed monensin either at 0, 11, 22, or 33 mg/kg of feed for 105 days. Fecal oocyst discharge during the first three days was highest with monensin 22 mg, lowest with monensin 33 mg and averaged 149.6 x 10(3) oocysts per gram feces for all lambs. Monensin at 22 mg/kg of feed reduced Eimeria ninakohlyakimovae and E. ahsata oocyst discharge. Organic matter and crude protein digestibilities were highest (P </= 0.05) in lambs fed monensin 22 mg/kg of feed. Monensin increased (P </= 0.01) rumen ammonia and propionic acid and decreased (P </= 0.01) acetic acid. Feeding monensin 33 mg decreased (P </= 0.05) feed intake by 5% and had no effect on gain or feed efficiency. Optimal responses were observed with monensin at 11 mg, feed consumption was not affected, gains were 8% higher (P </= 0.05) and feed was utilized 9% more efficiently (P </= 0.05) than the controls. In conclusion, monensin was an effective therapeutic agent against naturally occurring coccidial infections in early weaned lambs. Performance responses were largest with monensin fed at the rate of 11 mg/kg of feed.