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Animal Health: Important tips for selecting the right antibiotic

With most of the older antibiotics still available and several very effective long-acting antibiotics in use, the choice of products in front of the rancher or feedlot owner has never been greater. Some very effective drugs, especially those in combinations, have been removed from the marketplace over the years. The difficulty for producers — with so many factors hinging on the outcome — is deciding which antibiotic to use or if one is necessary at all.

One article cannot hope to clarify every possible combination, but in the end, work with your vet to decide on a strategy and list of choices for at least the common diseases.

Start with the label

Reading the label is always a good start. Diseases for which clearance has been granted to a particular antibiotic are written on the label. This alone gives you a start as to what types of diseases and subsequently what organ systems the antibiotic will get into. Most antibiotics, especially the new ones, require a prescription from your veterinarian. This ensures you know what it treats, dosage, method of administration, withdrawal and any other limitations.

Veterinarians weigh several factors before deciding the appropriate course of treatment. First, are antibiotics even necessary or will convalescence be sufficient? If there is no bacterial infection present or expected, antibiotics may be unnecessary.

On large mature cattle or feedlot animals the meat withdrawals definitely need to be considered. If a condition becomes chronic, slaughter may be an option. We don’t want to burden ourselves and the critter with a long slaughter withdrawal period. If daily care is better can we accomplish that or is the next best approach to use a long-acting product?

Other considerations will be the syringability (especially important in winter) dosage amount, safety, means of administration (subcutaneous, oral, or intravenous) and cost of the product per treatment day. The per-day figure is really the only way to truly compare treatment costs. The longer-acting products will cost more because they last longer. The upside is less labour necessary and subsequently less stress on the cattle when processing them. This may be nullified if other procedures or painkillers must also be given on a daily basis anyways.

The bottom line is there is a lot to consider.

Weigh the variables

The main decisions we as veterinarians and you as farmers make are what are the conditions, what organ system is primarily involved and what is the most likely causative bacteria. From these three main factors the most appropriate first, second and third choice of treatment is made.

These three choices might be made in different order on specific farms based on farmer preference, previous results or current research results. Veterinarians will even have different “favourites.” There is almost never a specific single choice.

A few antibiotics described as broad spectrum means they work against a wide array of bacteria in different organ systems. The older sulphonimides as well as newer drugs like “Nuflor,” “Resflor,” or “Excenel” are fairly broad in their effect. Other drugs, used for example in treating pneumonia, are very specific. The macrolide antibiotics are a class of drugs which specifically get into the lungs.

Drugs such as Zuprevo, Draxxin, Zactran and Micotil are all macrolides and are used primarily for bacterial pneumonia and only a few other things. All are prescription antibiotics are excellent for pneumonia but only a few other things. Veterinarians on your behalf may prescribe them for real specific things such as seminal vesiculitis in young bulls. There will never be a label claim against these oddball infections. That is where the veterinarians experience will become invaluable.

Classes of bacteria

There are two main classes of bacteria — gram positive and gram negative. Clostridial infections such as blackleg or foot rot are caused by gram positive organisms. We were always told at veterinary school “P” for positive and “P” for penicillin. This older antibiotic is still quite effective against certain conditions and most veterinarians still use some. Diseases such as blackleg produce toxins and the animal succumbs quickly so prevention in the form of vaccination is the only effective way to prevent this disease.

In order to be effective we must pick the right drug, administer it at the right time, and at the right dosage. Animal weight must be estimated correctly. These antibiotics have been formulated to be effective at the appropriate dosage. Administering a dose that is twice as much as necessary will not be more effective, will only cost more and result in an increased drug withdrawal. The safe rule is if you double the dosage you double the slaughter withdrawal. Always keep that in mind.

I would be remiss if I didn’t mention supplemental drugs such as those used as painkillers, anti-inflammatories, and appetite stimulants. In specific disease entities they are often given in conjunction with antibiotics to quicken or improve the response. Again, your vet can advise what works best.

The selection of the appropriate medication for the specific disease takes some thought. The biggest step saver is recording what products you use (record either the active ingredient or trade name) and list the diseases it is effective against as well as the dosage. Have a first and second choice. This will go a long way to making sure the appropriate product is given, especially by new workers

It might also help to post a drug dosage chart, available for most products, beside the chute. Have the slaughter withdrawal listed as well so drug residues don’t become an issue. †

About the author

Columnist

Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.

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