Vet Advice

A sudden death on pasture Dr. Sylvia Checkley  |   Back to Vet Advice

A dead animal out on pasture is an unpleasant and unexpected loss. "Sudden death" refers to an animal that is found dead but wasn't noticed as sick prior to death. Many diseases cause an animal to show signs of sickness for a few days before death. Some animals thought to be "sudden deaths" on pasture might have been observed ill in a situation where close daily observation was possible. Unfortunately this type of close observation is not possible for animals on pasture.

Occasional deaths do occur on pasture and are not necessarily a cause for alarm depending on the cause. However, a single death may also be the beginning of a disease outbreak. It is critical for all dead animals to have a postmortem examination (autopsy) done by your veterinarian as quickly as possible after death. The vet may also collect tissue samples for further laboratory workup. This is often needed to determine the cause of disease and is well worth the extra money.

Remember, carcasses deteriorate rapidly in warm weather making it harder for the vet to make a diagnosis. Call your vet ASAP.

Common causes of sudden death fall into a number of categories: infectious, nutritional or toxic. Infectious causes of sudden death include anthrax, blackleg and malignant edema.

Spores in the soil, dredged up by changing rainfall or drought patterns, are the most common way anthrax is spread. Anthrax tends to occur in the same areas over and over, once contaminated. The organism that causes anthrax (Bacillus anthracis) can survive 100 years in the soil, waiting for the right conditions to strike again. Vaccination for anthrax is available in high-risk situations.

Blackleg and malignant edema are diseases caused by clostridial bacteria (Cl. chauvoei, Cl. septicum, Cl. perfringens, Cl. sordellii, Cl. novyi). Clostridial spores are also spread in the soil.

With blackleg, the animal ingests spores then some type of trauma causes the spores to produce a toxin that causes severe muscle inflammation and death. You may see signs of lameness shortly before death but affected animals are commonly found dead. Often several animals from a herd are affected and larger herd outbreaks can occur.

Malignant edema often begins from a wound contaminated with soil. You might see swelling, skin discoloration at the wound, and a high fever. These animals usually die within 24-48 hours. This is not usually seen as a herd outbreak.

You can protect your animals from the clostridial diseases by vaccinating with a 7-way or 8-way vaccine recommended by your veterinarian. (This clostridial vaccine is very inexpensive and well worth it as blackleg, malignant edema and other clostridial diseases are very common in cattle.)

Some examples of diseases that could be considered nutritional causes of sudden death on pasture are pasture bloat, grass tetany, atypical interstitial pneumonia and white muscle disease.

Pasture bloat is caused by ingestion of legumes that form a frothy suspension in the rumen that prevents normal eructation (cud chewing). Gas continues to build up in the rumen and leads to tight expansion of the left flank and death if the bloat is not rapidly treated. Bloat-causing pasture is a higher risk in the prebloom stage. Management strategies and antifoaming medications are available to prevent pasture bloat; ask your veterinarian for more details.

Grass tetany is a magnesium deficiency that occurs after cows are turned out onto a lush pasture in the springtime. Lactating cows require magnesium for their milk, but can't get enough magnesium from some lush grasses to meet their needs. Affected animals have tremors, convulsions and belligerent behaviour. Early treatment is often effective.

Atypical interstitial pneumonia could also be considered a nutritional disease as it occurs a few days after cattle are turned out hungry onto lush pasture from poorer quality pasture. An amino acid (L-tryptophan) may be present in rapidly growing grass, especially in the fall. This is metabolized into a lung toxin (3-methylindole) in cattle that causes acute respiratory distress and lung damage.

White muscle disease, a deficiency of vitamin E and selenium, can stop the heart from working properly leading to sudden death. When other muscles are affected, we see symptoms of muscle weakness.

Many poisons or toxins cause symptoms before death. The first cases in an outbreak of lead poisoning, though, will often be dead animals. The young inquisitive animals get the highest dose of lead, which kills quickly. Other sick animals will be noticed in the following days.

Plants, like arrow grass, concentrate cyanide during drought and are more likely to be eaten by less picky animals. Cereal grains are more likely to concentrate nitrates, and Sorghum sp. are more likely to concentrate cyanide after plant damage such as drought or frost. Always test frost-damaged feeds before use.

Poisonous plants are often regional: water hemlock poisoning is an example of a plant poisoning that is seen occasionally. Blue-green algae blooms on bodies of water produce toxins that lead rapidly to death.

Organophosphates or carbamates are insecticides. Some are used to treat external parasites on cattle. They are poisonous in excess amounts. Symptoms include excessive salivation, dyspnea, stiff movements, diarrhea, twitching and convulsions.

An investigation of sudden death in a cow-calf herd can be carried out with your veterinarian. You should immediately take note of the location where animals died and any hints around the animal of what may have happened: signs of a struggle, discharge, burn marks or an animal down in a low area. Give your vet a thorough herd history, and include information on vaccination, changes in feeding, et cetera. All information you can give your veterinarian will help you come to a quicker more accurate diagnosis. Keep records for insurance purposes.

Lastly I will remind everyone that sudden death in groups of animals may be caused by lightning strike or electrocution. Please remember personal safety first in these situations!