Metaldehyde is a common ingredient in many slug baits, and is highly toxic to ruminants. It is sometimes combined with molasses, dangerously enhancing its palatability.
How Does It Work?
The way in which metaldehyde is toxic is poorly understood. It is believed that it reduces some types of inhibitory neurotransmitter (chemicals in the nervous system that help carry inhibitory nerve impulses). A reduction in these causes excitation of the nervous system and convulsions. The increased muscle activity from convulsions can cause severe electrolyte disturbances and a metabolic acidosis.
There is very little information on toxic doses in cattle. It is reported that a dose of 0.2g/kg has been fatal in adult cattle and that a calf died within 2 hours of licking an empty container that had previously held slug pellets.
What Are The Signs Of Slug Bait Ingestion?
Signs are often seen within 30 minutes of ingestion but can occur within 1-3hrs. If the bait is retained in the rumen, effects will be seen up to 12-24hrs later. Excess salivation, anxiety, tremors and an unsteady gait can lead to convulsions and in severe cases, death can occur in either 2-3hrs or 24-48hrs after onset of signs.
A history of exposure alongside the above clinical signs are often enough to diagnose metaldehyde poisoning, although it should be noted that other toxicities such as organophosphate poisoning or other conditions such as meningitis/CCN/ staggers or milk fever may look similar. Additional methods of diagnosis include:
- Post mortem analysis of gastrointestinal contents if still un-degraded
- Other post mortem signs such as nerve degeneration in the brain, congestion of blood vessels in the lungs, liver and kidneys due to hyperthermia are common
- Urine, blood and liver analysis can be performed, however are unreliable
There is no specific antidote, but aggressive symptomatic treatment in the first 24 hours may allow cattle to make a full recovery in the next 2-3 days. In particular:
- Activated charcoal can be administered orally to decontaminate the gastrointestinal tract and reduce absorption of slug bait
- Sedation may be necessary to help control convulsions
- Intravenous fluid therapy to rehydrate and correct the electrolyte imbalance and metabolic acidosis
Note: In milking herds, advice from APHA must be sought on testing milk prior to entering the food chain, alongside meat withdrawals for all cattle affected.
References: ‘Overview of Metaldehyde Poisoning’ – MSD Veterinary Manual