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Selecting The Right Antibiotic

The trick is to make the right choice. Hopefully reading this will help. One article cannot hope to cover every eventuality but it will give you a strategy and list of choices for at least the common diseases

With most older antibiotics still available and several powerful long-acting ones released, drug choices for the rancher or feedlot owner has never been greater. That doesn’t mean it will always be an easy decision. The trick is to make the right choice. Hopefully reading this will help. One article cannot cover every eventuality but it will give you a strategy and list of choices for at least the common diseases. Reading the label is always beneficial as it tells you the diseases the drug is licensed for and that alone is a good start to your selection process.

A veterinarian automatically makes several decisions in choosing an appropriate course of treatment.

First, you have to decide if antibiotics are even necessary or if convalescence is all that is needed. Is a bacterial infection present or expected in the near future?

With large mature cattle, withdrawal time for the drug is a consideration. If the condition becomes chronic slaughter may be the best option and we don’t want to burden ourselves, or the critter, with a long delay before it can be slaughtered.

Assess whether daily treatment is needed or if the disease can be managed with a long-acting product. Other considerations are syringability (especially in winter) dosage, safety, means of administration (subcutaneous, oral, intravenous etc) and the cost per treatment day. Cost per day is the most accurate way of comparing drug expenses. Longer-acting products cost more because they last longer. But they also take less time to administer and put less stress on the cattle. This advantage would be nullified if other treatments were already being given on a daily basis.

The three basic questions are: what is the condition, what organ system is primarily involved and what is the likely causative bacteria? The answers will suggest the most appropriate first-, second-and third-choice treatment. These choices will be in different order on each farm based on personal preference, previous results or current research results. Veterinarians will even have different favourites. There is almost never one specifichoice.

Some antibiotics are broad spectrum meaning they work against a wide array of bacteria in different organ systems. The older sulphonimides as well as newer drugs like Nuflor or Excenel and its long-acting form Excede are broad spectrum.

Other drugs are specifito a disease. Macrolide antibiotics are a class of drugs that move into the lungs. Drugs such as Micotil or Draxxin fit into this category and are excellent for pneumonia. At times veterinarians may prescribe them for other specificonditions such as seminal vesiculitis in young bulls. There will never be a label claim for these drugs against these oddball infections but this is where a veterinarian’s experience becomes invaluable.

There are two big classes of bacteria gram positive and gram negative. Clostridial infections such as blackleg or footrot 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 conditions like footrot.

Diseases such as blackleg produce toxins that animal succumb to quickly so prevention in the form of vaccination is the only effective way to prevent this disease.

To be effective we must pick the right drug, administer it in time and at the right dosage.

Weight must be estimated accurately when calculating the dosage. These antibiotics have been formulated to be effective at the appropriate dosage. Twice the necessary dose will not be more effective and will only cost you more and result in an increased withdrawal time. The safe rule is when you double the dosage you double the slaughter withdrawal. Always keep that in mind.

I would be remise if I did not mention supplemental drugs such as painkillers, anti-inflammatories and appetite stimulants. They are often given in conjunction with antibiotics to quicken or improve the response. Again your veterinarian can advise what works best with these drugs.

Selection of an appropriate medication for a specifidisease takes some thought. To save time in future, record the products you use (either the active ingredient or trade name), the diseases it worked against and the dosage. Have a first and second choice; this will go a long ways toward making sure the appropriate product is given, especially by new staff members. Have the slaughter withdrawal listed as well so drug residues don’t become an issue. This is all too much information to keep in ones head, so write it down.

To this new found knowledge, add epinephrine in case of an allergic drug reaction, appropriate syringes and needles and your treatment kit will be complete.

About the author


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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