Safety of elevated dosages of a 0.24% diflubenzuron pellet administered orally to horses

The safety of a feed-thru pellet formulation containing the insect growth regulator diflubenzuron (0.24%) for control of manure-breeding flies (Musca domestica L. and Stomoxys calcitrans L.) in horses was evaluated. Pellets were administered orally at 0, 1, 3, and 5 times the clinical dosage (0.12 to 0.20 mg/kg) on a daily basis for 31 consecutive days. Variables examined included daily clinical observations, hematology, coagulation, serum chemistry, acetylcholinesterase inhibition, body weights, and physical examinations. Horses remained healthy throughout the study, and no adverse reactions or events related to the pellets were observed. Statistically significant differences (P < or = 0.10) between dose groups (0x, 1x, 3x, and 5x) were observed for only four of the 44 serum chemistry and hematologic variables measured, none of which was dose related. Diflubenzuron can be safely administered orally to horses at 0.12 to 0.20 mg/kg for control of manure-breeding flies.