Large Animal Care

Almonte Veterinary Services is a full-service mixed animal veterinary clinic with scheduled, emergency, and after hours care. Our multiple mobile units serve dairy, beef, small ruminant, swine, and poultry clients in the Ottawa Valley.

Parasite Control for Dairy Cattle

Protocol 1: Herd Treatment
Dairy cattle should be dewormed as a complete herd in late fall after the first hard frost (see table 1). Use Eprinex Pour-On in lactating and dry cows and close-up heifers (60 days or less to calving), and Ivomec Pour-On in the heifers and calves. The Pour-On dewormers are for internal AND external parasites and are well suited to use in the fall. Herds with moderate to high level of exposure to worms should be dewormed again approximately six-weeks after spring green-up (July 1) with Safeguard Crumbles for this
treatment. It’s for internal parasites and using it in combination with pour-on dewormers in the fall helps control resistance to dewormers in your herd.

Protocol 2: Individual Treatment
Individual cow treatments are the least cost and most effective deworming strategy for lactating dairy cows to maintain each cow as free of parasites as possible during the first 100 days after calving:
a) low levels of parasites: give a single treatment just after calving.
b) moderate to high levels of parasites: give one treatment after calving, and a second two months later. Deworm the entire lactating herd approximately six-weeks after spring greenup (around July 1) with Safeguard Crumbles as well.

Combined Protocol:
The best overall deworming strategy for dairy cows may be a combination of both herd and individual treatments. Producers that haven’t maintained adequate parasite control in their herds in the past, for example, should begin with a whole herd treatment followed by individual treatments as their cows begin to calve. Alternatively, a whole herd treatment in
late fall with an effective dewormer will render the herd parasite-free until the following spring. Beginning in the spring, producers can individually treat their cows as they calve, and then continue this program until late fall or early winter when the whole herd treatment is given again. The individual treatments stop during the winter until the following spring.

The Details:
The right dewormer needs to be given at the correct time to ensure the greatest economic benefit while achieving maximum long-term parasite control. Deworming strategies are designed to control parasites by correctly timing the use of dewormers to interrupt the parasites’ life cycle and prevent reinfection before measurable economic loss has occurred.

Cows at Risk
The economic importance of parasitism in young animals, such as dairy replacement heifers, has long been demonstrated by many researchers, as symptoms of parasitism that develop in young cattle are easier to see and measure. Adult cattle can develop a strong natural resistance to parasites. However, during each lactation, in the period just following
calving, the cow goes through a period of “relaxation in resistance,” and considerable economic loss can occur if parasites are present during this period.

The period of greatest risk for cows to become infected by intestinal worms is during the first 100 days of lactation. Currently, high-producing cows are most susceptible to negative external stimulus, including parasite infections, as she is under considerable nutritional stress beginning at calving and continuing for several months, depending upon level of milk production.

Reduced Milk Production

A relationship exists among the time of exposure, length and degree of exposure, and the stage of lactation as far as economic loss is concerned. Three separate phenomena appear to be involved:
• Adverse effects of parasites to cows in early lactation may be manifested simply as added stress to an already stressed animal.
• Research demonstrates that lactation causes temporary depression of immunity against gastro-intestinal parasites.
• The presence of parasites has been shown to reduce appetite, reducing the cow’s ability to meet her nutritional needs during the period of peak production.

The effect of gastrointestinal parasites on production of lactating cows was first identified at the University of Wisconsin. In one study, dairy cows in various stages of lactation were experimentally exposed to infective larvae and responded with marked reductions in milk production. Cows that were less than 90-days fresh at the time of parasite exposure produced significantly less milk following the induced infection (-6.4 lb./day). No production loss was found in cows exposed to the experimental infections when the cows were more than 90-days fresh at the time of parasite exposure. The reduced milk flow in cows less than 90 days fresh was a result of the induced parasitic infections, adding further stress to an already stressed animal. It appears, therefore, that the key issue to establishing treatment for maximum economic benefit in controlling parasites in lactating dairy cows is simply to maintain cows parasite-free during the first 90 days of lactation.

Deworming dairy cows in late lactation or during the dry period is usually wasted because cows often become re-infected during the dry period. If they’re not retreated at calving, they can carry this infection through the early lactation period. Also, since the average dairy cow is under less physiological stress during late lactation, a deworming treatment at this time (as shown from the Wisconsin study) has little or no effect on improving milk production.

Strategic Deworming Program

The amount dairy cows are exposed to parasite contamination will determine the deworming program that should be used. The first step in designing a deworming program for lactating dairy cows is to determine the approximate exposure level to parasites throughout the year. Table 1 provides general guidelines for determining parasite exposure under different types of herd management.

If questions occur about parasite contamination levels, diagnosis of a herd’s parasite exposure can easily be accomplished using a lab test at the clinic called a fecal worm egg flotation technique. “Sugar Flotation Technique.”

Deworming cows that are harboring parasites at the time of calving will remove the parasites when the cows are just beginning their greatest period of lactation stress. If a moderate to high level of parasite reinfection occurs, the choice for the second strategictimed deworming is six weeks into lactation.

Treatment at calving and again six weeks following calving (0-6 program) is
recommended for several reasons. The length of the life cycle of gastro-intestinal parasites in the adult cow is approximately six to seven weeks. The six-week treatment is timely since one of the goals of strategic treatment is to remove any new infections acquired during
early lactation when high-producing dairy cows are milking near maximum production
and to prevent further worm egg shedding.

Table 2 outlines the recommended strategic deworming program based upon parasite exposure level. Once the approximate parasite exposure level is assessed, the recommended treatment program can then be determined.

Adapted by RG from: Donald H. Bliss, Ph.D., Veterinary Parasitologist, Verona, Wisconsin