Botulism is a progressive paralysis from the ingestion of a toxin found in rotting animal material or on the bones of dead animals. It is usually fatal, as it paralyses respiratory muscles. It is commonly associated with livestock chewing bones in an attempt to obtain phosphorus (P) when the pasture is deficient in it.
Pasture in many parts of Queensland is deficient in phosphorus due to a deficiency in the soil. However, in very good years, a relative deficiency of phosphorus may also occur in otherwise adequate situations. With rapidly growing pasture, energy and protein levels can be very high, and animals require high levels of phosphorus in their diet in order to utilise these nutrients. If phosphorus is not available in the pasture, animals may look to supplement the diet with bones. In these situations, botulism can occur.
Risks after flooding
After floods, decaying vegetation can be a source of botulism toxin. An immediate risk of botulism exists if animals consume carcass materials or decaying vegetation either inadvertently or in trying to meet a phosphorus need on marginal country. However, the risk may not arise until later in the year when the country dries a little, and the pastures recover and begin to 'explode' due to the moisture and nutrients deposited by the flood.
Maintaining an up-to-date vaccination program is the best approach to preventing botulism; however, phosphorus supplementation may also help animals make better use of vigorously growing pasture.
Phosphorus supplementation may supply the extra phosphorus if given early. However, if cattle develop a habit of chewing bones, this habit may continue after their phosphorus requirement is met or the requirement has passed, with the risk of botulism remaining.