Back in March I wrote about preparing for the mud that was going to result from the winter and spring we endured. I did so knowing that, like most years, our Dakotas climate would eventually dry out.
Well, for a lot of us, that hasn’t happened. Rains through the summer have put South Dakota and much of the middle US into the “extremely moist” category. While pasture grass growth has benefited, the advent of standing water looks to be causing some problems in cattle.
The column this spring mentioned feet and leg problems resulting from persistent exposure to moisture. In springtime, problems arise in cattle confined in muddy lots while we’re waiting for summer pasture to become available. In summertime, problems come from cattle’s access to stock dams and temporary sloughs, where standing in water provides a respite from hot humid conditions.
That relief from pasture heat is good, but problems can arise when persistent moisture deteriorates the natural defenses of the skin. Skin may be the most important – and overlooked – barrier between the bovine’s internal body workings and the nasty potential germs on the outside. Besides providing a thick physical barrier, the skin has its own community of good bacteria, yeasts, and other organisms that help deny pathogenic bacteria entry into the skin and deeper structures under the skin. Oils secreted by glands on the skin surface also create an antibacterial environment.
Persistent moisture softens the skin and disrupts the good surface bacteria and other antibacterial defenses. The thinner, more flexible skin in between the toes of a cow, bull, or calf is particularly vulnerable. This is where foot rot starts. Pathogenic bacteria (which are everywhere in mud, manure, and cattle environments) can then penetrate past the skin into a part of the foot where the relative lack of immunity helps it flourish.
Cuts and abrasions between the toes can similarly allow bacteria to enter. Once there, a foul, painful infection sets in. Left untreated, the problem can extend further into the leg and joints, even after the skin on the outside has healed.
But veterinarians in some areas are seeing rather unusual foot and leg problems besides the usual cases of footrot. These cattle, mostly adults rather than calves, have swollen lower legs and deep horizontal sores low on the rear aspect of their feet and legs. At first glance these look like wire cuts. Varying numbers of cattle in a given pasture are affected. The lameness is not typically severe; treatment seems to arrest the progression but healing doesn’t happen quickly.
The cause of this is still being worked out, thanks to pathologists at SDSU with cooperation from local vets. One of the initial worries was a newly-recognized bacterial infection of the bloodstream that some have associated with these problems. Once we got blood samples from affected and non-affected cattle, we found the germ wasn’t associated with this at all.
Another potential cause that has emerged is that of ergot toxicity. Ergot is a fungal infection of plants, affecting the seedhead of grasses like brome. When cattle eat enough of it, the toxin in the fungus causes small blood vessels in the extremities, like the feet, ears, and tail, to squeeze down, or constrict. We’ve associated tail switch loss in bulls and cows with ergot exposure. With the moist spring, ergot is certainly out there on headed-out pasture grasses in varying degrees. Most of the current feet problems don’t fit the textbook ergot presentation, which is a dry gangrene encircling the hoof where the skin meets it.
The one common thread for these cases is standing water on pastures. Ergot exposure can also cause cattle to have trouble regulating their body temperature, which might make standing in mud and water more attractive to the affected animal than usual.
When a cause of a problem isn’t definite, it’s hard to know what to do about it. Options for pasture without standing water or headed-out pasture grass are pretty slim. One thing producers can do, however, is keep an eye on their cattle and contact their veterinarian when lameness issues crop up.
As we’re finding this summer, all lameness is not the same – and having a vet sort out the various causes can help with treatment, prevention, and prognosis.