Deworming can significantly improve the average level of production in a cow-calf operation. Whether using chemical dewormer or pasture management strategies, the best way to control parasites will be unique to your operation.
Products to control parasite populations in cattle can be administered in a number of ways. Common methods include topical pour-on (with or without systemic absorption), injectable, and oral drenches. Treating internal parasites is best achieved via injectable products and oral drenches to ensure delivery of the desired drug dose. Pour-on products can be effectively absorbed systemically and provide a good dose. However, more variability exists with this method of administration if the weather is not cooperative.
Bottom line is to ensure each animal receives an adequate dose based on its body weight regardless of the route of administration. Basing the dosage off of body weight helps attain the best efficacy as under dosing will not eliminate all the parasites while promoting resistance and overdosing can be harmful to the animals and add an unnecessary expense.
Parasite resistance develops over time from repeated use of the same deworming products. The more frequently a dewormer is used, the quicker that resistance will develop. Monitoring effectiveness of treatment can help you determine if and when switching products is necessary.
Cattle build up resistance to parasite infestations slowly and younger animals are more at risk of clinical disease. The most important populations to manage for parasites are weaned calves, heifers and second calf cows. Older cows have had the opportunity to develop resistance and should not require annual or semi-annual treatment in the absence of clinical signs.
Pasture management through rotation, alternate species grazing, haying and rotational tillage can significantly reduce the number of infective larvae on a pasture. Focused deworming of individuals showing clinical signs of parasitism rather than mass treatment of groups can be very effective in promoting overall herd performance, reducing the development of resistant parasites, all while reducing the level of contamination of pasture.
Maintaining appropriate stocking densities to prevent overgrazing can also help limit parasite exposure.
Work with your veterinarian to determine a parasite control strategy that fits your situation.