Illness in horses following spraying with amitraz

Abstract

Sickness occurred in 3 of 4 horses within 24 h of being sprayed with an 0.025% w/v aqueous suspension of amitraz. The latter consisted of a portion of an amitraz aqueous suspension made up some 3 weeks previously, to which some freshly prepared spray fluid had been added. It seemed likely that the amitraz in the older solution had broken down to the highly toxic N-3, 5- dimethylphenyl N-methyl formamadine derivative and that this was in fact the main cause of the untoward effects observed. The horses displayed typical clinical signs of tranquillisation, depression, ataxia, muscular incoordination and impaction colic lasting up to 6 days. Subcutaneous oedema of the face occurred in one horse. The syndrome was accompanied by mild dehydration and acidosis. All horses survived after persistent symptomatic treatment including the giving of intravenous fluids, enemas, analgesics every 3 h, multiple doses of paraffin oil per os and dexamethasone intravenously. Following the eventual relief of constipation the horses scoured profusely for 24 h before their condition returned to normal.