Clinical practices are reporting a resurgence of older external parasite issues, such as lice mites or flies.
There are also more external parasite issues with ticks as tick species ranges move north.
In the past, it seemed when ivermectin came into use we treated yearly and all external parasite problems were eliminated, such as lice and most fly issues.
We then needed longer treatment for fly control, and insecticide ear tags came along that gave two-plus months of control but resistance seemed to develop.
Read Also
Alberta eases water access for riparian restoration
Alberta government removes requirement for temporary diversion licence to water plants up to 100 cubic metres per day for smaller riparian restoration projects
To minimize resistance developing, best practices are to switch between different groups of insecticides. The issue is all insecticides I am aware of are in Group 3 with few new products coming out.
This happened a few years ago when malathion was no longer available for use in cattle oilers. Producers gobbled up several years’ supply so they had time to determine the next effective management tool.
In managing parasites, your veterinarian needs to diagnose the parasite involved, such as biting or sucking lice, or the type of mange.
Once a specific parasite is determined, you must determine if there is a sufficient amount to warrant treatment and the most appropriate time to treat. If new symptoms are observed, or if symptoms return shortly after treatment, it may indicate parasite resistance to the drug or the diagnosis was wrong.
In the last year, I have talked to veterinarians who have diagnosed ticks (tick paralysis), mange mites and very aggressive flies that resemble horse flies.
This shows that we need to share the results with fellow producers so they are aware of the types of parasites in their areas.
Ticks in general are moving north, so we must be aware of this. In some cases, it may warrant spreading the word so others can be on the lookout.
Tick reporting already exists for small animals and is especially important because ticks can carry and spread other diseases.
When ticks are identified, the current treatments where ticks are indicated on the label are effective. The one problem I see developing is that often production animal species like goats or bison are not on the label so technically the product can’t be used on them.
Insecticides come with their own sets of rules so prescriptions can’t be written on them by veterinarians in this country.
The good news is down the road, products will be developed or adapted from the small animal sector that have broad spectrums to internal and external parasites. There could be another product coming out before long that is as effective as ivermectin was when it first came out. They are just getting approved in other countries so I hope regulatory agencies approve them quickly so producers in Canada will have access to these products.
We must all show responsibility by using parasiticides only when needed and according to label directions.
If there is a diagnosis of itchiness in cattle, we must explore the cause. It is often assumed to be lice or mange but that is not always the case. From allergic reactions to sunburn to nutrition issues, there are many causes and if the cause is parasites, you should be able to find them or do a skin biopsy to help with the diagnosis.
Also, be aware of products that may no longer be available even if temporarily. That happened this year with Sabre, a permethrin that was pulled until the label is changed. This cuts down our choices but other products are very similar such as Boss or Cylence, so if products become scarce, ask your veterinarian about the most appropriate replacement.
Also, lice seem to disappear in the summer so there is no need to treat past spring. As well, parasite resistance, internal and external, is genomically present in cattle so selecting and breeding cattle for this may help ease lice issues.
Certain insecticide products are available to buy in many locations so make sure you know the dosage, how the product is applied and what control is expected.
It is good to know if the treatments worked because if not, there may be a misdiagnosis or resistant parasites.
There was resistance to ivermectin but its efficacy may be improving because it is being used less around the globe. It was a fantastic product in its day and so for decades it was the main product we used for external and internal parasites until resistance developed.
Gone are the days of treating with the same product at the same time and expecting the same results.
Sometimes it might be possible to miss a treatment, so review both internal and external parasite control on a timely basis with your herd veterinarian.
Roy Lewis works as a veterinarian in Alberta.
