Ask the Vet

Dr. Ken McMillan, Contributing Columnist

READER: For the last few years, we have planted ryegrass and used that to carry our steers to 7- and 8-weight before selling them in the spring. Our area has been in an extreme drought, and we have given up on ryegrass this year. We want to sell the steers, but we vaccinated and dewormed them. The label says, "Cattle must not be treated within 48 days of slaughter for human consumption." We are not selling them for slaughter, so does the withdrawal time still apply to these steers?

DR. McMILLAN: Kudos to you for reading the label and asking. I believe the answer centers on how the cattle are marketed. If you take them to the stockyard, in most cases, there would be no mechanism to shift your responsibility to the new buyer or buyers. In this case, I believe you would be in violation of the law and could be held liable if residues were detected in these cattle. If they were sold through a board sale or by private treaty, a paper trail is created, and in my opinion, the responsibility would shift to the new owner or owners.

But, this is my opinion. If anyone knows for certain, please contact me.

READER: What can you tell me about the new dewormer that recently came on the market?

DR. McMILLAN: I assume you are referring to Valcor. This new dewormer contains two different classes of antiparasiticides. I believe this is a product whose time has come. Let's review how we got to this point.

There are only three classes of antiparasiticides currently available for cattle in the United States. Benzimidazoles, often called "white dewormers," include Safe-guard/Panacur (fenbendazole), Synanthic (oxfendazole) and Valbazen (albendazole). Benzimidazoles require oral administration and come as pastes, liquids for drenching, blocks and pellets. Imidazothiazoles were available as injectable, bolus and paste forms (Tramisol, Levamisole and others) many years ago but, until Valcor, were only available as a powder for oral use. The macrocyclic lactones (Ivomec, Dectomax, Cydectin and generics) are available as pour-ons or injectable formulations.

There is significant and growing resistance to the macrocyclic lactones in my opinion because of the indiscriminate use of pour-on products. To paraphrase a colleague of mine, "Cheap, easy and good rarely come in the same package," and some of the generics got really cheap. These products got used for fly control or on cattle with no diagnosis and were often underdosed. White dewormer use dramatically decreased when the pour-ons came to market in large part because they required more effort.

I never stopped recommending the use of white dewormers, and I have used for several years a combination of a macrocyclic lactone and a white dewormer on cattle I suspected of having resistant worms. Research -- especially in small ruminants -- has shown that combining two or three classes of dewormers can be effective in controlling resistant worms and slowing the development of more resistance.

Valcor combines doramectin (Dectomax) and levamisole in an injectable form. I believe Valcor will have a place in controlling resistant worms. It will be a part of my recommendations, and we have used it on our yearling cattle. Please note its dose is 1 milliliter (ml) per 55 pounds of body weight and not the traditional 1 ml per 110 pounds, so the volume will be twice as much as other injectable dewormers. There are additional instructions on the label not seen with other injectables, so I would encourage you to visit with your veterinarian about those.

A more important takeaway from the introduction of this product is that we need to be smarter about how we manage parasites. If we do as we have always done, parasites will develop resistance to this product. I encourage you to meet with your veterinarian to evaluate your current parasite control program and develop the best program possible for your operation.

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-- Please contact your veterinarian with questions pertaining to the health of your herd. 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.

-- These are only my thoughts and general guidelines. Please get with your veterinarian and together develop the best program for your herd.

-- Email Dr. Ken McMillan at vet@dtn.com

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