With the advent of the reliable pour-on and injectable endectocides found on the market today scratching from lice or mange is a very rare occurrence in cattle herds except when a fall treatment is neglected. As a veterinarian, I am sometimes called on to investigate apparent breaks in the efficacy of these products. In doing this I have observed a lot more about cattle’s scratching behaviour that I ever knew before because lice or mange were always blamed in the past.
When called out by the pharmaceutical companies rep to investigate scratching its important that the cattle be closely examined. A visual observation over the fence is not enough. We examine several affected animals and usually clip an area surrounding the worst affected areas on individual animals. Careful visualization with the naked eye or a magnifying glass can detect some external parasites, if they are present. Deeper skin scrapings are taken as well because we don’t want to miss any mange mites, if they are around.
My experience is that the companies that make these products are very conscientious and want to know the cause of an apparent breakdown. Failures are rare but when they do occur the usual culprits in Western Canada are biting lice (Damalina Bovis spp.) or chorioptic mange. This is because both of these external parasites are surface feeders. They move around a lot so control may never be quite 100 per cent.
They also jump quickly from one animal to another so when new animals are introduced to the herd it doesn’t take long for a new infestation to spread around.
One of the first questions we ask on these visits is when and how long ago new introductions were brought in and whether or not they had been previously treated.
This together with proper dosage and administration based on accurate body weights are extremely important factors to examine when trying to find out why these cattle are still scratching. Guns for applying endectocides now disperse the product more accurately over the back.
Other causes of scratching are varied in the herds we see during these investigations.
Ringworm is commonly seen around the eyes and head. If severe it will cause irritation and scratching especially in young cattle. If the infection is in another location one has to look closely at the animal to find the circular lesions. One treatment for ringworm will usually get these cattle on the road to recovery.
Bale processors and other grinders do a great job chopping and dispersing feed. The only negative is all the dust and debris that ends up in the hair of the cattle. In warmer weather when the animals are sweating this scurf and debris can cause intense itchiness in certain locations. Once cattle start rubbing these itchy spots the skin can become scraped and sore and start to bleed, adding to the problem.
A lot of these scratching incidents often follow unseasonably warm spells during the winter, after the cattle have haired up.
Free-living mites in grain or bedding are another common cause of itching in cattle.
Certain individual and genetic strains of animals may be allergic to certain feeds or molds present. These allergic reactions will vary in severity but many will cause reddening of the skin and swelling associated with itchiness. In these cases the allergen must be removed before recovery can happen.
A nutritional deficiency is another possibility if it affects the health of the skin. Trace minerals should always be fed as part of the overall nutritional package. Important ones in skin health are zinc, copper and vitamins especially Vitamin A. Unhealthy skin allows various bacteria to take hold. The infections that result can be intensely itchy and spread locally.
Show cattle when washed must be thoroughly rinsed otherwise the residual soaps can cause irritation or allergic reactions.
Some rubbing and licking is part of cattle’s natural grooming process. It is only when this occurs in excess to the point where hair loss and damage occurs to the skin that we should be concerned and investigate.
Constant irritation regardless of the cause can result in weight loss and a predisposition to other diseases. Dropping feed consumption and anemia can result from blood loss especially when sucking lice are involved.
At the other end of the scale, increasing feed consumption in winter could be due to the hair being rubbed off from an animal’s coat. In deep-freeze weather this is stressful and more energy is required to keep the creature warm.
By routinely using an endectocide treatment most parasitic causes of scratching will be eliminated. If scratching continues have the problem fully diagnosed so preventative measures can be taken to eliminate the problem in the future.
— Dr. Roy Lewis, DVM