Approaches for a field diagnosis of abamectin poisoning in calves

Abstract

An approach for the diagnosis of an abamectin outbreak in calves in the field is described and discussed. In a Midwestern Brazilian property, nine out of a 52 newborn calves were affected and died, making up for morbidity, mortality, and lethality ratios of 17.3%, 17.3%, and 100%, respectively. Major clinical signs included tremors in various muscle groups, inability to stand, and difficult, wheezing breathing. Each affected calf had been treated subcutaneously with abamectin (0.4mg/kg/body weight). No lesions were found at necropsy or at histological examination. Major diseases of newborn calves were included in the differential diagnosis.

Assessment of Avermectins-Induced Toxicity in Animals

“…Various studies have also indicated the avermectins to have toxic effects on animals [ 26 , 27 , 28 , 29 ]. For example, collie dogs experiencing severe illness presented to the clinic were found to be suffering from ivermectin toxicity [ 30 ].…”

Doramectin intoxication in malnourished 15-month-old cattle

“…Macrocyclic lactones promote the inhibitory action of the GABA neurotransmitter, which may lead to generalized muscle hypotonia and cause the death of intoxicated animals. Most animals recover with or without supportive treatment, and lethality ranges from 50-100% (Riet-Correa 2007, Guizelini et al 2020). Considering the weight of the animals (150kg), the therapeutic dose of doramectin indicated would be 3ml; however, the bovines received a dosage compatible with animals weighing 250kg, 1.6 times more than the recommended dose.…”

“…The varied and nonspecific clinical signs and the absence of pathological findings make the diagnosis of macrocyclic lactone intoxication a challenge (Guizelini et al 2020). The association of the history of overdose with the clinical course and the absence of gross and microscopic lesions are decisive to the diagnosis of the intoxication.…”

“…Although macrocyclic lactones are used on a large scale in animal production due to their efficacy, prolonged action, and safety margin, cases of intoxication frequently occur in Brazil, especially with abamectin in calves (Riet-Correa 2007, Guizelini et al 2020. As well as botulism, urea or organochlorine intoxication, intoxication by macrocyclic lactones should be a differential diagnosis of diseases affecting the nervous system that do not produce gross or microscopic changes in ruminants.…”

“…In Brazil, abamectin intoxication frequently occurs in calves under three months of age (Riet-Correa 2007, Guizelini et al 2020, Borges et al 2021. The use of abamectin in cows with suckling calves has caused intoxication and death in their calves under 50 days of age (Borges et al 2021) Macrocyclic lactones are widely used as endectocides in farm animals.…”