Ionophore toxicity causes muscle damage with incoordination, leg weakness, diarrhea, dyspnea, and reduced feed intake and weight. Stunting may also occur. Type I (“red muscle” or oxidative) fibers are most susceptible, and lesions are most prominent in the leg musculature. Lesions may also be found in heart and gizzard muscle. Adult birds (chickens, turkeys, ratites) and birds with no previous exposure are more sensitive to ionophore coccidiostats. Gross and histologic changes are similar to those of nutritional myopathy (see Myopathies: Nutritional Myopathy in Poultry). Ionophores promote movement of cations across the cell membrane, causing disruption of the ionic equilibrium, increased intracytoplasmic concentration of Ca2+, and cell death. The toxic dose of ionophores is decreased if they are used in conjunction with tiamulin, erythromycin, or chloramphenicol.

Coffee senna (Cassia occidentalis) toxicity can produce clinical signs and gross and histologic changes in muscle similar to those seen in ionophore toxicity.

Last full review/revision March 2012 by Arnaud J. Van Wettere, DVM, MS, DACVP