While calf milk replacer and meal are fantastic for rapidly growing young calves, these products can pose a very serious danger to dogs and other non-ruminant animals. Many calf feeds contain coccidiostat medications known as ionophores, such as monensin (Rumensin) or lasalocid (Bovatec). Cattle and other ruminants are able to digest and process these ingredients safely, but monogastric species, including dogs, pigs and horses, cannot. Other sources of ionophores include certain types of chicken feed, bloat capsules and feed additives like Rumensin.
Ionophore toxicity affects skeletal muscles and the heart muscle, causing paralysis. This may look like generalised weakness and a staggering gait, alongside dilated pupils and increased heart and breathing rates. Weakness often starts in the hind limbs, but gradually affects the whole body, resulting in an inability to walk. In the worst cases, animals can develop heart failure and some may even die due to respiratory failure. Animals that recover from an acute toxic exposure could be left with permanent damage to their muscles and nerves, with lifelong repercussions.
The toxic dose of ionophores varies depending on the species. Dogs are not quite as susceptible as horses, with even tiny doses possibly having devastating consequences. However, there can also be a cumulative effect - if your dog gets repeated small exposures over time, this can eventually lead to toxicity. This is why you might hear stories of dogs having got into a small amount once without appearing to be affected. Certainly, it is not worth taking the risk of finding out what amount might cause a toxic effect and it is simply best to avoid all exposure!
Unfortunately, there is no specific treatment or antidote to ionophore toxicity. In the event that toxicity does happen, the goal is to remove the toxin from the stomach and/or give medications that will bind to and inactivate it. The sooner this can be done following ingestion, the better chance of success. Supportive care may then be necessary to get them through the acute phase of the toxicity. Signs of toxicity develop within 12 hours of ingestion. If your dog gets into a product containing ionophores, it is definitely an emergency situation and you should contact your veterinarian as soon as possible.
As is often the case, prevention is better than cure. Dogs living in rural environments such as farms and lifestyle blocks are at particular risk. Have a careful look to see if you have any products containing ionophores on your property. If you do, make sure to always store them away safely, and when feeding your livestock, ensure that your dogs do not have access to them either.