Several things come to mind when we analyze the most recent success that cattle producers have had in reducing respiratory disease and deaths.
Vaccines have improved and cover a broader range of respiratory pathogens. Seven main virus and bacteria vaccines can help protect cattle against respiratory disease.
Lessening weaning stress with good nutrition and parasite control is also effective.
Macrolide antibiotics are a key component in reducing sickness and death from respiratory disease in large feedlots or when cattle are gathered, commingled and transported.
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The macrolide family is often used metaphylactically, which means as a preventive method when there is a good chance a high percentage of cattle are at risk of getting respiratory disease or have already been diagnosed with it.
All products in this family of antibiotics have a similar chemical structure.
Withdrawal times are longer, as long as 49 days before slaughter. It makes sense because they accumulate in the lungs and other tissues.
The products include Micotil, Zactran, Draxxin and Zuprevo, which came out on the market last year. All of them require a prescription and must be bought from a veterinarian. Producers need to have a working relationship with their veterinarian so that they can advise where and when to give macrolides and help develop treatment protocols.
This approach costs money, but death loss in medium sized feedlots in Canada can be reduced to about one percent, which is a huge improvement.
Macrolides generally have an affinity for respiratory tissue. Half-lives can sometimes be long, which means they stick around in the lungs and lung fluids before being excreted.
This can take as long as two to four weeks, depending on which product is used.
Cattle are assessed a risk level either at home or on entry to the feedlot as low, moderate, high or ultrahigh. An appropriate antibiotic is then prescribed.
Veterinarians will have their favourites based on effectiveness, price, dosage, route of administration, bottle size and syringeability, which is important in cold Canadian winters.
These softer features may not be critical if you have a small herd, but dosing 20,000 cattle could make a huge difference on labour costs. All the macrolide antibiotics are quite syringeable.
The risk level of the cattle being treated will be a major factor when selecting product.
Cattle are considered at high risk if they are commingled, come from an auction market or are transported long distances.
This applies to most cattle that are weaned and shipped through the auction system in Canada.
Even weaning in inclement weather may tip the scales from low-risk to high-risk calves.
Animal health companies have manufactured a dosing syringe in which the calf’s specific weight is dialed into the syringe.
The setting can be changed on the fly to match the dose to individual calves.
The use of macrolides can provide a window of time and allows cattle to settle in and get on feed before much observation is necessary. This also reduces the labour needed to pull sick cattle from the pens.
Effectiveness against bacteria varies, but effectiveness of almost a month has been demonstrated in some products.
Micotil had issues early on with safety and self-injection, but producers can avoid self-injection by practising good beef quality assurance, properly restraining the animal and watching how they inject.
Many studies have compared morbidity and mortality, and most veterinarians take these into account before deciding which macrolide to prescribe.
Having these choices is good for the industry because it creates competition.
It is also good if supply problems arise or we see resistance developing, although resistance has not been an issue with macrolides.
Something occasionally goes wrong in manufacturing, and products are recalled. That is why producers and their veterinarians need to develop a good protocol and know what alternative macrolide can be used to treat a specific respiratory disease.
Veterinarians and producers should also strive to implement management practices that further reduce respiratory disease such as preconditioning programs. This could decrease the necessity for antibiotics over time.
