Ask the Vet

Deworming Doesn't Solve Every Problem in Calves

If you've dewormed your calves, but they still have worms, don't automatically assume it's a case of resistance. (Progressive Farmer photo by Becky Mills)


We have a small group of calves we weaned about two months ago. They've been wormed and vaccinated, and are on hay and a little feed. One is losing weight and has diarrhea. The rest seem fine. What do I need to do?


If you have a veterinarian who is familiar with your operation, give him or her a call, and discuss this with them. If you do not have a veterinarian who knows you and your operation, I would suggest calling one and getting him or her to come out for a look over your cattle and your operation.

Lately, I have had several similar cases where owners bring in a stool sample, and, when we check it, the calves are heavily infected with worms or worms and coccidia. This is a simple and economical test that is tremendously underutilized.

There are many reasons calves that have been dewormed can still have worms. A calf can be missed. Also, we see more resistance to some dewormers -- especially some of the generic pour-ons. Many times, when calves are weaned, they are turned into the same lot calves used in the recent past, and the environment is heavily contaminated with parasite eggs and oocytes. These areas often get muddy, and feedbunks, troughs or pans become contaminated with mud and manure. So, clean pastures or lots, and improved sanitation helps prevent reinfections. Nutrition is also very important. As I have noted before, calves must have a ration that meets their energy, protein and mineral needs. Healthy cattle are much more resistant to all diseases.

Another disease that should be considered is persistent infection with bovine virus diarrhea (BVD-PI). Calves are infected during pregnancy and accept the virus as "normal." Many of these calves can be smaller and sickly, but some appear normal. All BVD-PI calves shed massive numbers of viruses continuously, so they are a threat to other calves in the herd. This condition can be controlled with testing and vaccinations.

Get a veterinarian involved to know for sure what the problem is. Find out what is happening in your herd, then develop an ongoing herd-health program to keep your operation and your animals healthy and profitable.


Editor's Note:

Please contact your veterinarian with questions about the health of your herd or other animals. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice but is purely for informational purposes.

Email Dr. Ken McMillan at