Ask the Vet

Making Informed Decisions

There are two types of feed-through fly control products. Which works best for you? (Thinkstock image)


I read your column about fly control and I am interested in using the fly-control mineral blocks you mentioned. The label on the Rabon Oral Larvicide gave me pause, as it states it's for weaned cattle and indicates a vet should be consulted before using it in pregnant or nursing cattle. So is it OK for nursing calves to lick the block? Can pregnant cows be impacted? Could they abort?


You have done well. I wish more people would read the label and ask before using a product. I contacted Manna Pro and asked them about this warning. They said the EPA requested it be added to the label in the last few years.

This product has been on the market for years with no documented issues I have ever heard of, but I went back and reviewed the safety data. I am comfortable that the product is safe for use in herds with calves and pregnant cows.

I would still recommend everyone check with their veterinarian to get an opinion on this. I say this because in the unlikely event a problem occurs, it will be your local veterinarian who tries to help you. It's best these professionals are always in the loop when making any decisions regarding your herd's health care.

As a point of clarification, there are two types of feed-through fly-control products. Some contain an IGR, which stops the normal development of the immature stages of the fly in manure. The other option, the Rabon you mentioned, is an insecticide that kills larvae in manure.

My personal experience has been with the IGR products. There are no restrictions on their use of which I am aware. I have not seen any independent studies proving one type of feed-through fly control to be superior to the other, but I would appreciate input from readers based on their experiences.

These type of products should be started before the fly season begins to be most effective. This option is not for everyone and is just one tool from the toolbox of fly control.