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Animal Health

Integrated Pest Management Helps Control Cattle Lice

Written by Scott Schell and Derek Scasta

The cattle biting louse, Damalinia (Bovicola) bovis, is unfortunately making a comeback in Wyoming.  With advances in veterinary parasite treatment products over the last 35 years, significant economic losses due to parasite infested cattle have become rare. However, if lice are not properly controlled, the speed at which cattle biting lice can proliferate on a cow that is already stressed by winter weather and pregnancy is rapid.

Cattle biting lice cause cows to rub off portions of her hair coat, worsening weather stress and negatively impacting her health and developing calf.  Reports from this past spring indicate that heavily pregnant cows trying to relieve the relentless itching caused by lice became trapped on their backs and slowly suffocated. The choice of parasite control product, the application method chosen, the timing of treatment and the length of residual control has played a role in the resurgence of cattle chewing lice problems.

The veterinary products containing macrocylic lactones (ML) class parasiticides, such as  ivermectin, avermectin, eprinomectin, abamectin, doramectin and moxidectin active ingredients, were first sold starting back in 1981. The ML class of active ingredients can control both internal parasites – like gastrointestinal worms, flukes and cattle grubs and external parasites – such as ticks, mites and lice.  Before the discovery of the ML molecules, good parasite control required at least two different products and separate applications to get broad spectrum control of all types of cattle parasites.

The MLs are typically applied to cattle with an injection or as a pour-on formulation when the cattle are gathered and being handled for other management practices, such as weaning or pregnancy checking. ML products are popular due to their ease of use, low cost and broad spectrum effectiveness. 

However, there is growing concern that cattle parasites are developing resistance to this class of valuable management products.  One of the ways parasites start to develop resistance to a control product is through under-dosing.  It is theorized that sub-lethal exposure to any pesticide can allow the survival of individual pests with genetic trait(s) that allow them to de-toxify the product.  Repeated sub-lethal exposures to the same active ingredient eventually leads to selection of pest populations with even greater resistance. 

Brown stomach worm, Ostertagia ostertagi, populations have been already been identified as having resistance to the ML products. To date, no cattle biting or sucking lice populations have been documented with resistance to the ML products.

To insure that each animal treated gets the correct dose, the injectable formulations of the ML are frequently recommended over the topical, or “pour on,” formulations.  Injectable ML products are effective for internal parasites and the external parasites that feed on blood such as winter ticks and the sucking lice species. 

However, cattle biting lice don’t feed on blood and are not controlled by the injectable parasite treatments. Topical ML treatments can control all susceptible internal and external parasites, if the correct dosage is absorbed through the animals’ skin.  Improper dosages of ML can happen if not adjusted for variation in cattle body weight, for example, if producers give a 1,400-pound cow the same dose as a 1,000-pound cow. Additionally, wet and muddy or dry and very dusty hair coats inhibit ML absorption, and cattle licking/grooming behavior can which can cause overdosing in the licker and under-dosing in the cow being licked.

Fall is the traditional time for applying treatment to manage parasites that impact cattle health.  In Wyoming, mid-October through November is considered to be ideal timing for the control of all cattle lice species.  Cattle biting lice populations start expanding as the cattle’s hair coat thickens and the microenvironment next to the skin becomes ideal for them to feed and reproduce in. If lice treatment is done too early, the surviving cattle biting lice can rapidly reproduce and cause problems for the cows later in the winter. If the treatment is done too late, the cattle will have started to expend energy scratching, start to damage their winter hair coat and be distracted from eating before the lice are killed.

The length of the residual control with any parasiticide product is important. For example, lice egg shells are difficult to chemically penetrate, and they are not feeding on the animal at this stage. If the length of residual control is shorter than the incubation period of the egg, the baby lice will hatch and suffer no mortality. A minimum two-week post treatment residual or retreatment after 14 days is necessary. 

Considering that cattle biting lice are predominantly female, with one study reporting a sex ratio 322 females to every one male, and they can reproduce asexually, any eggs that survive a treatment can rapidly re-infest a cow. Topical ML formulations can provide residual control against cattle biting lice much longer than 14 days. This provides protection from lice hatching from eggs or the physical transfer of adult lice from any infested animals the treated cow might contact.

If you have treated your cattle this fall with an injectable ML product, it is prudent to monitor your cattle for signs of cattle biting lice irritation through the fall and winter. Cattle intensely scratching their poll, neck and withers to the point of hair damage are a sure sign of cattle biting lice infestations. Lots of insecticide products formulated as spot-ons, dusts, sprays or ear tags are labeled for cattle biting lice and are suitable for a rescue treatment. 

Consulting with your herd health veterinarian and reading the information on cattle lice control products, found at the High Plains IPM website at wiki.bugwood.org/HPIPM:Cattle_Lice, can help you choose a product compatible with your herd.