Effect of the ionophore Lasalocid on face fly (Diptera: Muscidae) larval survival and physical and chemical parameters of cattle feces

Lasalocid added to a cattle diet at recommended concentrations (200 mg/head/day) did not cause substantial decreases in face fly survival or changes in the size or weight of pupal exuviae. However, additions of lasalocid directly to the dung in concentrations of 41 μg/g or greater caused significant reductions in puparial physical characteristics as well as survival. Reductions in survival ranged from 20% at 41 μg/g to 98% at 208 μg/g. Similarly, length and weight of pupal exuviae were reduced 1.5 and 3.9 times, respectively, for larvae reared at the 167 μg/g level. The toxicity observed at this level was related to changes in physical and chemical properties of the cattle feces, including a twofold increase in all organic acids measured: acetic (2.2 times), butyric (3.0 times), propionic (2.4 times), and lactic (1.6 times). Increases in organic acid levels were associated with a decrease in pH and increases in osmolality.