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Heavy spring rainfall may be cause of increase in blackleg

Progressive Dairyman Editor Audrey Schmitz Published on 07 August 2017

In many cases, cattle death is the first sign of a blackleg outbreak. By the time the disease can be identified, it’s often too late. In the last month, the number of blackleg cases in beef and dairy herds have been up all across the Southeast.

The diagnostic labs especially have seen a lot more positive tests for blackleg than in past years.

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“I have been practicing for 30 years, and I have never seen this many cases,” said Darrell Wester, DVM, a mixed animal veterinary practitioner in Thompson, Georgia.

In his area alone, Wester said he has seen six to eight different farms, two of which were dairies, affected by the blackleg outbreak.

“What has been really strange this year is: It’s sort of out of that routine age bracket,” Wester said. “We are seeing older animals come down with blackleg, and we are seeing much younger animals come down with it as well.”

The disease generally affects animals between 6 months and 2 years old. Once contracted, the animal usually dies within 12 to 48 hours.

“If you catch them real early, you may notice limping,” Wester said. “But most of the ones I get called to are already down and will have air under their skin and usually a large swollen muscle group.”

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The first observable signs are lameness, loss of appetite, rapid breathing and a high fever. Characteristic swellings develop in the hip, shoulder, chest, back or neck. At first the swelling is small, hot and painful, but as the disease progresses, the swelling enlarges and becomes spongy and gaseous.

“It is just terrible when you go to a farm and see they have four or five of these animals down at the time,” Wester said. “They will call me when they see one, but I have honestly been there on a farm looking at one and look over elsewhere and see another one go down.”

Blackleg is caused by Clostridium chauvoei, a bacterium most frequently found in the soil of pastures. This clostridial bacteria produces long-lived endospores extremely resistant to environmental conditions such as heat, drought and chemical disinfectants. Blackleg is an infectious disease, but it is not contagious and does not pass from one animal to the next.

A blackleg infection begins when an animal ingests these endospores. The endospores are then deposited in the animal’s body tissue and lie dormant until they become activated in an anaerobic (oxygen-deficient) environment. Muscle tissue that has been damaged will have compromised blood flow; as a result, oxygen will not be as readily delivered to the affected area.

Therefore, any activity that causes bruising can promote the disease.

Blackleg is almost entirely preventable by vaccination. The most commonly used clostridial vaccination in cattle is the 7-way type called Ultrabac 7. It is referred to as “7-way” because it protects against other clostridial diseases such as malignant edema, black disease and enterotoxemia.

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It is generally recommended to vaccinate calves between 2 and 3 months old followed by a booster four to six weeks later.

“I’ll be honest, I have been vaccinating some sooner than 3 months because I was seeing calves succumb to the disease at 2 months,” Wester said. “At a very young age, their immune system may not respond to the vaccine, so this is why in the past we didn’t do it. But because we saw those young ones die, we began vaccinating them three times instead of two.”

Since he started implementing in the additional vaccinations, Wester said he hasn’t seen a case now in over a week.

“It definitely hit all of a sudden, and I was seeing it multiple times a week and then – boom – it quit,” Wester said. “I don’t know if the increased vaccinations worked or if the storm of disease is just over.”

Wester speculates the cause of the increased blackleg cases in the Southeast are due to the above-normal rainfall the area has received this year. He thinks the environmental conditions this year have been more conducive for the endospores to rise to the surface of the ground in flooded areas and be more available for infection.

“Nobody has really offered a reason as to why we are all of a sudden having more cases,” Wester said. “But I can tell you, in the last few years we have been experiencing drought, and then this year we seem to have had more rain.”

A regular vaccination program is the best insurance policy to protecting one’s herd. Dairymen should work with their veterinarian to create a herd health plan and determine specific vaccinations for their area. For best results, always follow the manufacturer’s recommendations for dosage, method of administration, number of times given and proper storage.

After a blackleg disease outbreak occurs, carcass disposal should be done carefully.

“Do not perform a necropsy in the field where the animals are,” Wester said.

“Never would you open the animal there for risk of contaminating the soil even worse.”

Wester’s advice is to take the dead animal completely away to a separate area for a deep burial and to cover the carcass in lime.  end mark

Audrey Schmitz
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Percentage of Operations that Vaccinate Preweaned Hiefers against Clostridial Diseases 

According to the most recent USDA Dairy Cattle Management Practices in the United States report, only 26.7 percent of large dairy herds of 500 cows or more vaccinate pre-weaned heifers against clostridial diseases.

Additionally, only 12 percent of dairy herds in the eastern region of the U.S. vaccinate compared to 25 percent of herds in the western region.

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