An itch that needs scratching
March 5, 2013
For ranchers who always pour their cattle and herd bulls at preg-checking time in the fall, to see the cows starting to rub on fence posts makes them scratch their own heads with confusion. Isn't that pour-on working?
A common mistake ranchers make is assuming the product doesn't work when an animal starts to lose hair in the winter months due to lice, according to Russ Daly, DVM, South Dakota State University veterinary extension specialist.
"When producers pour for external parasites in the fall, they are certainly killing the active lice," he said. "But, it can be difficult to get rid of the dormant lice that is hiding between the folds of skin. That's why it's very common to see lice reappear in the winter months."
Economically, a cow or bull that is burdened with lice will cost a rancher money. The scratching cow is tough on fences and buildings as they rub to relief themselves of the itch. A pregnant cow might be further stressed because of the lice and could have troubles calving or nursing. A herd bull with lice may lose weight or be set back during the winter months, when he is supposed to be getting back in shape before breeding season.
There are two kinds of lice – sucking lice, usually found around the head and neck of cattle; this type can cause anaemia – and, biting lice, which feed on skin debris, blood and scabs; this type is the most irritating and is found on the neck, shoulders, back and rump. Symptoms of lousy cattle include rubbing, biting, scratching and resulting hair loss. Stressed or diseased animals will develop more severe lice infestations than healthy cattle.
"It seems kind of odd, but right now is a good time to be thinking about external parasites," said Daly. "This is the time of year we start seeing the clinical sides of lice – rubbing on fence posts and losing hair. It's not uncommon at all to see the cattle scratching again even though they were poured in the fall. A common mistake ranchers make is thinking the pour-on used didn't work, so, we try other products and are frustrated that the issue persists. In reality, what was active at the point of pouring was taking care of, but the lice hiding in the folds of the skin are hard to get."
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In an ideal world, Daly said it might be advisable to wait until late December to pour, although he knows it isn't always convenient and feasible to do so. Whenever a rancher chooses to pour for external parasites, it's important to do the entire herd.
"It is prudent to realize you may have to pour twice because it's hard to get all of the active lice at one time," he admitted. "Once in a while, there are other concerns that cause animals to scratch, but it's usually one or two, not the whole herd. If the problem is persistent, look at the dosage of the products you're using. Make sure you're in the right dosage range. It's pretty easy to set that pour-on gun for that 1,100-pound cow, but there are probably bigger cows than that in the herd."
Another issue Daly warns about is another external parasite – ticks.
"In some parts of our state, we do see tick problems," he said. "This time of year is a common time to hear reports of ticks in cattle, especially along creeks. Some of these ticks are called winter ticks. They tend to get more active this time of year, relative to the spring of the year, when we think of ticks coming out. In some of these cases, we have weak, skinny cows who aren't as healthy. So you have to ask the question, did the ticks make the cow debilitated, or was a run-down cow open for ticks to take advantage of?"
Keep an eye out for clinical signs of the reappearance of lice in cattle previously poured.