Sudden death in pasture calves? Blackleg should be on the list

Carla was too far away to identify the object over on the side hill. But something in her gut told her it wasn’t good. This trip to check cattle was overdue by a couple days. Now she wished she’d been out here sooner.

As she guided the 4-wheeler toward the base of the hill, her suspicions were confirmed – it was a dead calf, and one of the nicer ones too. She texted her husband with the bad news. It wasn’t pleasant, but she knew it was part of raising cattle. It looked like too much time had passed in the hot July sun to figure out what happened to this calf.

A scan of the rest of the herd found the other cows and calves alive and well – until the next day. Carla’s heart sank when she found another dead calf, another good one, up by the mineral feeder. She remembered the calf’s tag number from yesterday – he’d been perfectly healthy. What could be going on? The week had been dry with no storms. She couldn’t imagine lightning being the culprit.

This calf had not been dead too long. Maybe there was a chance to find out what happened. Carla found the number for the vet clinic on her phone. One of their new vets was close by and could get there soon. After giving directions to the pasture, Carla waited for Dr. Kevin’s arrival.

Dr. Kevin had just graduated from vet school this spring, and his mind was running through the list of possibilities even before he retrieved his posting knife from the vet box. His vet school training kicked in as he systematically went through the calf, organ by organ. Nothing in the chest or the abdomen looked abnormal, he thought. Kevin knew that sometimes a cause of death just can’t be determined. But he hoped like heck this wasn’t one of those times. An answer of “I don’t know” isn’t going to impress this first-time client of his!

But Dr. Kevin was not done. He sliced through the thigh muscle in one of the rear limbs. Bingo. What should have been pink muscle tissue was instead dark brown and filled with small gas pockets. A smelly red-black fluid oozed from the cut surface. This sealed the diagnosis: blackleg.

When Carla heard Kevin say “blackleg,” her heart sank a little more. She knew his next question. And the answer was no, they hadn’t vaccinated the calves for blackleg before they hit pasture. This spring was one big time crunch. Besides, no one ever remembered a case of blackleg on the farm. This summer, the calves were grazing without protection.

Kevin explained that blackleg is caused by a bacteria, Clostridium chauvoei, that can survive for years in spore form on most pastures. Calves eat the spores while they’re grazing. Those spores travel through the calf’s gut and are carried by white blood cells to muscle tissue, where they lie dormant. When something like a bruise or pulled muscle occurs, the bacteria activate, multiply, and produce toxins. Those toxins kill off the muscle tissue (creating the lesions Kevin found on post-mortem), and shut down the calf’s vital organ functions, resulting in a sudden death. What’s worse, Kevin explained, is that faster-growing, better-muscled calves are usually the ones affected. For reasons mostly unknown, it’s calves – not cows or bulls – affected by this disease. Vaccines normally give good protection, however.

During his explanation, Carla could only think of one question – are more calves going to die? They could, was Kevin’s answer. If spores caused problems for these calves, other calves are at risk too. We should do what we can to help prevent blackleg from killing more calves, he explained. Carefully gathering calves for a blackleg vaccination (in the form of a “7-way” Clostridial), and possibly antibiotics to control any impending infections, were recommended.

Carla took away two big messages from the experience. First, especially given the value of a calf, taking time to vaccinate calves with a 7-way at turnout would have been a very valuable use of the family’s time. Secondly, it pays to check cattle daily so problems like blackleg can be nipped in the bud.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.