Botulism in cattle – an ongoing concern

Date published: 20 July 2016

The Department of Agriculture, Environment and Rural Affairs (DAERA) has confirmed that cases of botulism continue to occur in Northern Ireland following results of tests carried out by the Agri-Food and Biosciences Institute (AFBI). Investigations by the Veterinary Sciences Division of AFBI have provided strong circumstantial evidence that broiler litter is a risk factor for many of these outbreaks.

DARD news

Botulism is caused by Clostridium botulinum bacteria that produce toxins under certain environmental conditions. The bacteria are commonly found in the environment and will grow to high levels in decaying organic matter including animal and bird carcases. It is believed that contamination of broiler litter with the carcases of chickens that have died, from various causes during production, can render the litter dangerous for ruminants.

Even small fragments of carcases transferred onto pasture by scavenger animals, such as foxes, dogs or crows may pose a risk to grazing ruminants.

Scavengers may gain access to this material during storage or following spreading on land. While the Animal By-Products (Enforcement) Regulations (NI) 2015 permits the spreading on land of poultry litter, the spreading of litter contaminated by carcases is an offence under the Regulations.

Symptoms of Botulism

Cattle and sheep of all ages are susceptible to botulism, which is characterised by progressive muscle weakness (paralysis). Affected animals may be weak, stagger about or go down. Cattle characteristically display flaccid paralysis and occasionally protrusion of the tongue. In most cases the disease is fatal although some animals may recover. In many cases of botulism euthanasia is justified on welfare grounds. Cattle are extremely sensitive to the effects of the toxin meaning that ingestion of very small amounts of toxin can result in clinical disease. The progression and severity of the disease depends on the amount of ingested toxin. When a large amount of toxin has been ingested, the animal may be found dead without having shown any signs of disease. Conversely, if only a small amount of toxin is ingested the progression of the disease may take a more chronic course and clinical signs may be less severe.

Diagnosis of Botulism

Diagnosis of botulism is based primarily on clinical signs and a history of known exposure to risk factors such as contaminated broiler litter or carcase material. Laboratory confirmation is frequently difficult and relies on detection of the toxin in samples harvested from suspect cases and elimination of other possible causes of disease.

Control of Botulism

Careful disposal of all animal or bird carcases and poultry litter is essential to minimise the risk of botulism to livestock. Poultry carcases should be promptly removed and disposed of by incineration or rendering as required by the Animal By-Products (Enforcement) Regulations (NI) 2015. Following removal of the broiler crop, all poultry house doors should be kept closed until the litter is removed. The litter should not be removed from the house until it can be loaded directly onto spreading equipment, covered vehicles or immediately stacked and covered. At no time should it be accessible to dogs, foxes, crows or other scavengers that may carry carcases onto adjacent pasture or into livestock housing. Washings from poultry houses and yards should be collected in tanks rather than be allowed to flow onto adjacent land.

The Nitrates Action Programme (NAP) Regulations (NI) 2014 also provide further controls in respect of the storage and spreading of poultry litter which help prevent the spread of botulism. The regulations require that where poultry litter is stored in a field heap, it must be compact and covered by an impermeable membrane within 24 hours of placing it in the field. This helps prevent the spread of the disease by scavenging animals which gain access to poultry carcasses after litter has been stored. The NAP Guidance Booklet provides advice to farmers on how to reduce the risk of botulism to grazing animals from poultry litter.

Poultry litter should not be spread on agricultural land that is to be grazed, or from which silage or hay is to be harvested, in the same year. This is because fragments of carcases, containing botulinum toxins, may persist on pasture for a considerable time. If litter must be spread, it should be deep-ploughed into arable ground. If this is not an option and litter must be disposed of by spreading on pasture, ruminants should not have access to the treated fields for at least several months. However, there is no guarantee that the treated fields would then be safe for cattle and it is important to remember that fragments of carcases on pasture may be transported by scavenger animals and birds to neighbouring fields. Spreading litter on a windy day may also pose a risk of contaminating adjacent fields.

Any animal or bird carcases, or portions of carcasses, visible on pasture or in livestock houses, should be promptly removed. Even small fragments of such material may be dangerous to livestock and should be disposed of by incineration or rendering, as required by current legislation.


Two vaccines are available under “special treatment certification” for the protection of cattle at risk of botulism. Veterinary surgeons may apply for to the Veterinary Medicines Directorate (VMD) however, vaccination should not be used as a substitute for preventing exposure of cattle to poultry litter that may contain carcass material.

Further information on botulism can be found on the DAERA website.

Notes to editors: 

  1. Botulism is a severe, often fatal, form of blood poisoning which can affect most animals. It is caused by toxins produced by bacteria which are present in high levels in decaying organic matter such as bird and animal carcasses.
  2. Investigations by AFBI’s Veterinary Sciences Division have shown strong circumstantial evidence that poultry litter is a risk factor for many outbreaks of botulism. The risk is linked to carcasses in poultry litter, which are taken by scavenging animals and transferred onto pasture.
  3. Spreading poultry litter on pasture is not recommended. If it is spread on pasture, animals should not be allowed onto that pasture until at least the following grazing season. 
  4. Given our limited arable area and large poultry sector, a significant amount of poultry litter is currently spread on pasture.
  5. Botulism in cattle is characterised by muscle tremors, weakness, paralysis and death. The progression and severity of the disease depends on the amount of ingested toxin.
  6. The risks to humans from outbreaks of botulism in cattle linked to poultry litter are very low. This is because the toxin types involved in such outbreaks have rarely been associated with human disease.
  7. The FSA requires that all meat and milk from clinically affected animals should not enter the food chain. However, there is no need for restrictions on the sale of milk or meat from clinically normal animals in affected herds.
  8. Two vaccines are available under “special treatment certification” for the protection to cattle at risk of botulism. However, vaccination should not be used as a substitute for preventing exposure of cattle to poultry litter that may contain carcass material.
  9. All media enquiries to DAERA Press Office, or tel: 028 9052 4619.

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