Real parasite control involves more than the administration of dewormers. Even with the advances in product efficacy, a thoughtful, rational strategy of their use is required to minimize the adverse affects of internal parasites.

The problem
Even moderate worm burdens can affect the general health and growth of youngstock and the production of lactating cows. Immunosuppression, anemia, and physical damage to the GI tract are three of the primary results and can lead to clinical problems.

In youngstock, poor growth and condition can delay puberty and lower early-conception rates, therefore delaying the age to first calving. In lactating cows, milk-production losses seem to occur in the first 100 days of lactation, since milk yield post-calving is related to energy balance and body condition (fat reserves).

Trials I have conducted show that proper deworming at freshening (versus dry-off), with follow-up treatments if needed, yields an increase of up to 250 pounds of milk during that lactation. In treated cows, peak milk increased by 1 to 2 pounds per cow.

Design a plan
Parasite-control programs must be designed for an individual farm because no two operations are alike. Facility design — dry lot, free-stall, tie-stall or grazing — will all impact parasite-control programs. But that is just the starting point.

Determining the level of infestation of the different animal groups and of their environments is required. Fecal examinations — where parasite burdens are quantified by the number of eggs per gram of feces — are an effective tool to assess individual animal burdens, as well as the contamination level in the animals’ environment. This test also can be used to evaluate drug efficacy and the overall success of your program. 

Management decisions on cow movement and grouping also will help determine when a product may be needed to help break the worms’ lifecycle.

Proper implementation
Multiple products are available for use in dairy cattle. However, under-dosing is the most common cause of product failure. (Proper dosing is critical.)

Dosage is based on animal weight, so you need to do more than guess. Use a scale or weigh tape. While weigh tapes are not 100 percent accurate, they will provide a close estimate of the animal’s weight. 

Products should be chosen based on your findings from the fecal exam, the class of animal (lactating or non-lactating), and the availability of facilities and labor. Individual dosing and administration yields the best results. However, mass medication of groups with feed-additive dewormers can be used successfully if bunk space is adequate for all animals to consume the appropriate dose. As always, read the label and follow the withdrawal times for meat or milk.

As with most products used on the farm, timing of the treatment is vital. Administrations are generally designated for stages of life or production, changes in grazing patterns and pasture rotation, or the turnout onto new lots.

Re-infestation post-treatment has been another cause of program failure. The dewormer may have been effective in clearing the initial worm load. But if the animal or group is returned to infested pastures or pens, the parasite levels can return to pre-treated numbers in less than two months. A second dose four to six weeks later is required in these situations to break the parasites’ life cycle.

Parasites cost the dairy industry millions of dollars in production loss and mortality every year. Work with your veterinarian to develop a strategic plan that fits your operation.

Jim Brett is a practicing veterinarian in Montezuma, Ga.