Parasites impact every aspect and segment of cattle production – feed conversion, immune response, milk production, reproductive performance and overall health. Recent data demonstrate the economic and environmental impact of a strategic deworming program.
On average, there are 46 added pounds at weaning per calf for cow-calf operators practicing strategic-timed deworming. There is another 10% improvement in breeding efficiency, plus significant improvement in body condition scores in cows (additional 40 to 60 pounds).
A lot of producers deworm and think their cattle are clean, but we know they are not. The bottom line is: You should see a 90%+ reduction in fecal egg count after deworming. If not, the following can happen due to subclinical worm infection:
- Decrease in feed intake, average daily gain and milk production
- Poor immune response from viral vaccines and diseases
- Resistance to dewormers may keep increasing
- Reduction in pregnancy rate
Merck Animal Health has maintained the world’s largest database of fecal egg count reduction test (FECRT) results. The database has more than 24,000 fecal samples – about half conducted pre-treatment and half post-treatment – from 24 states and more than 250 veterinary clinics.
The database results indicate the endectocide formulations – both pour-on and injectable – are losing efficacy. The 10-year summary shows they performed in the 51% to 58% efficacy range, which is well below the desired 90% efficacy threshold.
The various fenbendazole formulations had an efficacy of 98.7%. Using two classes of dewormer (endectocide plus fenbendazole) to concurrently treat cattle resulted in an efficacy of 99.1%.
It is important to note that even slight improvements in using two classes of dewormers simultaneously can have a major impact on drug efficacy long term.
Getting the best deworming results
The good news is: You can manage resistance by using existing technology and strategic parasite management protocols. Recommendations include:
- Work with your veterinarian to do FECRT testing. It is important that 20 samples are taken both at treatment and 14 days post-treatment. If there is less than a 90% reduction in fecal egg count, a polymerase chain reaction (PCR) test – which is a DNA-based test – should be conducted to determine which parasites remain. These tests are not expensive.
- Use two or more classes of dewormer at the same time. There are three classes of dewormer approved for use in U.S. cattle – benzimidazoles, endectocides or macrocylic lactones, and imidazothiazoles, with the first two being most commonly used. Using both a dewormer with an active ingredient that ends in “-ectin” and another with an active ingredient that ends in “-zole” will produce the highest efficacy.
- Give the full-labeled dose. If you are dosing based on the average weight of the group, you’re actually underdosing some of animals, which can contribute to reduced efficacy.
- For cattle on pastures, timing is especially critical. Cattle should be relatively parasite-free at the start of spring grazing season. This deworming can take place any time from the end of the previous grazing season until the time just prior to the start of the new grazing season. A second deworming is necessary in order to develop and maintain parasite-safe pastures through the grazing season. For cow-calf, this deworming should take place approximately four to six weeks after the start of the spring grazing season or when calves are approximately 200 to 250 pounds. Using feed and mineral forms of deworming, such as range cubes, dewormer blocks or mineral, require relatively little labor. In fall-calving herds, cows should be dewormed prior to calving followed by a second deworming given to both the cows and calves once a majority of the calves have reached at least 200 pounds.
- Refugia, the practice of leaving some parasites unexposed to a dewormer, can slow resistance. The goal of refugia is to create a system that allows you to dilute out some of the resistant parasites with susceptible parasites.
Work with your veterinarian
Now is a good time to start the conversation with your veterinarian and discuss diagnostic testing and on-farm management practices that should be used to create a strategic parasite program that is most effective for your operation.
References omitted but are available upon request by sending an email to the editor.
A Minnesota veterinarian’s perspective
Using diagnostics to ensure effective deworming
Erin deKoning, DVM, of the Rock Veterinary Clinic in Luverne, Minnesota, serves both cow-calf and feedlot clients in the southwestern part of the state as well as into nearby South Dakota and Iowa. Working in conjunction with parasitologist Dr. Donald Bliss, her clinic has offered parasite evaluation clinics (PEC) sponsored by Merck Animal Health in addition to their in-clinic diagnostic services.
“Dr. Bliss evaluates results from each producer’s herd and gives a clear picture of what the operation is facing from a parasite load standpoint,” says Dr. deKoning.
Dr. Bliss also has helped determine strategic deworming strategies based on the diagnostic results. “Several of our feedlot customers receive cattle from different areas of the country, often carrying different species of parasites than we typically might find in this area,” she explains.
No matter what type of operation, Dr. deKoning recommends concurrent deworming. “If we use a pour-on ivermectin alone, we only get about 50% efficacy. Our standard protocol is to use two classes of dewormer – endectocide and fenbendazole – at the same time.”
She adds: “We show our clients the math. If you spend that additional $3 per head on concurrent deworming, you only need 2 pounds of added weight to justify the cost. The actual weight gain advantage far exceeds that. Concurrent deworming will more than pay for itself.”
Dr. deKoning says they work with their clients on the timing of their deworming program, including summer deworming protocols. “We incorporate non-handling forms of deworming when cattle are out on summer pastures to minimize labor,” she says.
The PECs illustrate what exactly is going on in an operation. “In a tough market situation, it’s easy to look for what you can cut,” Dr. deKoning explains. “With the PECs or our in-house diagnostics, I can reference the work and help the producers recall what we saw from a worm standpoint in their operation and why a strategic deworming program is essential.”
