Acute ionophore toxicosis in pigs

Animal Health Laboratory – Toxicology section, University of Guelph, Guelph, ON

AHL Newsletter 2019;23(3):11-12.

Acute deaths were reported in a pig farm after feeding a new diet for 12-24 hours. A non-specified number of animals weighing 35-60 kg died within 24 hours, while sublethally affected animals showed clinical signs consisting of incoordination, stumbling, hind-end weakness, and ataxia. Some tail biting and ear tip necrosis were also noted. Most animals improved upon removal of the diet; however, some were euthanized because of welfare reasons.

Blood work on 1 severely affected animal showed the following biochemical changes: CK: 217,940 U/L (RI: 50 – 3,531), AST: 4,561 U/L (RI: 16 – 65), K: 9.9 mmol/L (RI: 2.1 – 7.1) and P: 3.74 mmol/L (RI: 1.16 - 2.97). Of 7 blood samples tested, 4 consistently showed elevated serum CK and AST activities, compatible with ongoing muscle injury (rhabdomyolysis). Considering clinical presentation, laboratory test results, and history of recent diet change, feed samples were submitted to the Toxicology section of the Animal Health Laboratory (AHL) for ionophore quantification. Samples from 2 different bins contained salinomycin at 320 and 390 µg/g (ppm), respectively; monensin and narasin concentrations were below the limit of quantitation (< 1.0 ppm). The target dose of salinomycin in the feed was 25 ppm, as recommended,¹ however, a mistake was made on the prescription and the final concentration was high enough to cause acute toxicity (reported lethal doses in pigs: 166-720 ppm of feed^2,3). Most survivors had recovered one week after the incident; however, a few animals still showed hind-end weakness and lameness.

Ionophores are feed additives used as coccidiostats or to improve feed efficiency; however, overdose or inadvertent exposure of non-target species can cause toxicity. Clinical signs of salinomycin toxicosis in pigs are typically related to the gastrointestinal and muscular (skeletal more than cardiac) systems. Affected animals commonly have anorexia, lethargy, stiffness, tremors, recumbency, and may be reluctant to move. They may also have diarrhea. Clinicopathologic changes are related to degenerative myopathy consisting of elevated serum CK and AST activities, as well as some electrolyte changes, in particular hyperkalemia. Rhabdomyolysis can also cause myoglobinuria and possibly renal disease as a result of acute tubular damage. Clinical signs may appear within 24 hours, and some animals will continue to show problems after several days or weeks. Prognosis is guarded when the intoxication has caused significant heart damage. Animals surviving the acute phase may recover but weight gain and other parameters might be compromised.

       Table 1. Cases of ionophore toxicosis confirmed at the AHL in recent years.

References

1. (http://www.inspection.gc.ca/animals/feeds/medicating-ingredients/mib/salinomycin-sodium-sal-/eng/1331066179898/1331066230292#a2)

2. Feed-associated toxicants. In: Plumlee KH. Clinical Veterinary Toxicology. Mosby, 2004.

3. Plumlee KH, et al. Acute salinomycin toxicosis in pigs. J Vet Diagn Invest 1995;7:419-420.