Treatment with potassium bromide mitigates ataxia and reduces tremor in lambs with perennial ryegrass toxicosis

AIMS: To assess the use of potassium bromide as a suitable therapeutic intervention for perennial ryegrass toxicosis (PRGT) by reducing the clinical effects of lolitrem B intoxication in sheep. METHODS: Neurological signs consistent with PRGT were induced in male lambs aged between 10–12 months by ingestion of a known dose of lolitrem B toxin in feed (0.16 mg/kg/day). Lambs were treated with the anti-epileptic drug bromide either daily from onset of trial (a loading dose of 540 mg/kg over three days then 20 mg/kg daily PO) or with bromide at a single dose of 300 mg/kg PO at a time-point based on clinical criteria. Ataxia, tremor and other physiological parameters including faecal cortisol metabolites, were monitored over time to evaluate efficacy of the treatment as compared to control groups. Serum and CSF bromide levels were assayed to assess therapeutic exposure in CNS and somatic tissues. RESULTS: Measurement of muscular tremor activity by average Root-Mean-Square (RMS) voltage from triceps electromyography (EMG) were decreased in bromide treated group (group 3) (0.0342 mV) compared to intoxicated animals not receiving bromide (group 2) (0.0608 mV, p=0.045). Degree of ataxia determined by mean composite gait score was also reduced in group 3 lambs (8.78) compared to group 2 lambs (21.71, p<0.001). General neurological signs improved to the extent that only two of nine lambs treated with bromide continued to drop into sternal or lateral recumbency on gait analysis despite while lambs in Group 2 lambs showed further deterioration of clinical signs. CONCLUSIONS: This trial suggests bromide can mitigate the neurological signs associated with PRGT in sheep. CLINICAL RELEVANCE: Alleviation of the neurological signs associated with ingestion of the neurotoxin lolitrem B during outbreaks of PRGT in livestock is of key importance to improving clinical outcomes, reducing mortality and improving productivity in both New Zealand and Australian production systems, and worldwide.