Lasalocid and monensin in finishing diets for early weaned lambs with naturally occurring coccidiosis.

Early weaned male crossbred lambs (n = 90) with an average weight of 14 kg were used in 6 groups to evaluate the efficacy of monensin (22 mg/g of feed) and lasalocid (12.5, 25, 50, and 100 mg/kg of feed) on naturally occurring coccidiosis. Average 24-hour oocyst output at the start of the experiment ranged from 5.7 x 10(6) to 156.7 x 10(6) for monensin-treated and 100-mg lasalocid-treated groups, respectively. Monensin and lasalocid were effective against Eimeria ninakohlyakimovae of E ahsata. To day 103, body weight gains were similar for the 4 groups fed lasalocid (336 g/day) and averaged 6% higher (P greater than 0.05) than did gains in control and monensin-treated lambs. Feed efficacy averaged 9% higher (P less than 0.05) for lambs fed 25, 50, and 100 mg of lasalocid/kg of feed and 7% higher (P greater than 0.05) for lambs fed monensin and 12.5 mg of lasalocid/kg of feed. There were no treatment effects on digestibility, although lasalocid tended to increase (P greater than 0.05) crude protein digestibility (values were higher on day 76 than on day 28). Lasalocid and monensin were potent manipulators of rumen fermentation. Increasing the amount of lasalocid in the feed was associated with successive increases (P less than 0.05) in molar proportions of propionic acid and decreases (P less than 0.05) in acetic acid. Lasalocid and monensin controlled naturally occurring coccidiosis and improved performance in early weaned lambs (45 days old) under feedlot conditions.