Ask the Vet

Hair Loss on Cows, Calves

Possible cause of hair loss are many, but could be as simple as flies or gnats. (DTN/Progressive Farmer photo by Karl Wolfshohl)


Several of our cows and calves have red, circular areas of hair loss. I have seen ringworm and lice, but these do not look like that. They seem to have improved after we worked them and weaned the calves. Do you have any ideas what this is?


Over the years, we have seen similar problems here in the Southeast, caused by a hypersensitivity to insect bites. While flies are the most visible biting insects affecting livestock, biting gnats can also cause irritation. This condition is similar to dogs with flea allergy dermatitis. Some dogs have a hypersensitivity to the saliva in flea bites. These dogs will scratch and lose hair and can develop severely infected skin. Other dogs in the same house with even more fleas may show minimal or no signs. This can also occur in cattle and other animals too, including humans.

I bet when you worked your herd, you also treated them for flies. This could be why you saw the improvement at that time. Also, weather conditions and seasons change, which could lead to improvement.

Certainly, there are other potential causes including photosensitization, herpes mammillitis virus, ringworm and dermatophilosis (rain rot or rain scald), to mention a few. If the problem recurs, a skin biopsy can give you a definitive diagnosis