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Survey reveals improvement needed in parasite management

Animal Health with Roy Lewis: Internal and external pests need different treatments

Over the last few years there has been a lot written about internal worm control, timing of chemical treatment and parasite resistance. A group of researchers from the Western College of Veterinary Medicine in Saskatoon asked producers in 2015 about how they were using internal parasite treatments. The researchers drew some good conclusions from this survey that may guide how internal and external parasite treatment should be undertaken.

The researchers included Doctors Wills, Parker, Waldner, Uehlinger and fellow columnist John Campbell. They sent questionnaires to more than 100 producers across Western Canada, receiving replies from almost everyone. They were able to draw several important conclusions.

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You may wonder why it took five years to get this information out, but it’s a process. First, the information is gathered, collated, and then has to be thoroughly checked before it is accepted in a journal. It usually takes about 18 or so months from the time an article is submitted until it is printed due to the backlog. These refereed journals make sure of the scientific accuracy of the article and don’t want writers pre-releasing anything until the work has been concluded. No information is a lot better than false information.

The 2015 survey showed most producers treat with a pour-on insecticide product in the fall, mainly to control lice. About half the producers treated calves in the fall and the other half in the spring. Most producers opting for a later fall treatment for internal worms and lice did not generally need to apply a product in the spring.

With the average grazing period of about five months, it was found that most producers supplied water to livestock from surface water sources, so adding deworming or other medications through the water supplies definitely did not work in these situations.

In most situations, producers used a parasite-control product only once a year but in some cases several times a year. If multiple treatments were applied to improve efficacy, it appeared producers should consider changing to a more effective product to reduce cost and improve control measures. Multiple treatments might also lead to resistance. More is not necessarily better.

One concern with spring application of a product such as a macrocyclic lactones (ivermectin-type product) is potential harm to the beneficial insects such as dung beetle.

Testing for parasite load

Most still used the pour-on Ivermectin products but the other class of dewormer such as the benzimadazoles (brand names such as Safeguard and Valbazen) were fairly common too.

Only about five to 10 per cent of producers used an oral drench product or administer products through feed or minerals. However, the use of feed-supplied products appeared to be increasing as producers aim to improve efficacy, particularly in the fall when lice populations are rising.

A couple of different products may be needed as some pour-on products, for example, are specific for lice, flies or ticks but may do nothing to control internal worms. Topical products like Saber, Boss, Cylence and Ectiban for cattle oilers come to mind.

More producers, but still less than one-third, are getting their clinics to determine parasite loads with periodic fecal exams. There is lots of room for improvement here. The fecal count will determine the severity of a parasite load, but in some cases, fecals may show just a low level with no treatment required. They may also monitor how effective a product is and whether there’s a need for retreatment.

Once a pasture is contaminated the cattle need to be dewormed regularly. Preferably, that would involve a follow-up treatment in midsummer, about six to eight weeks or so after turnout.

It was found that parasite loads were higher in herds that used good rotational grazing as cattle are grazing closer to manure packs where the larvae are. Rotational grazing is good for a number of other reasons but it can concentrate parasites somewhat. These higher parasite loads are even found in B.C. where cattle generally run on huge tracts of land, however, most grazing is happening in the very fertile lush meadows and around watering areas where pasture productivity is greatest.

While pour-on products applied in the fall have been effective, there also appears to be a real resurgence in problems with lice in the winter. The common practices that have stood the test of time need to be altered with proper timing, proper product selection and proper administration of products to control internal and external parasites. Both are very resilient and we need to figure out ways to outsmart them!

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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