Deworming: When is it Profitable to Deworm?

Knowing when to deworm your cattle can be quite profitable.
By: Michelle Arnold, Large Ruminant Extension Veterinarian, University of Kentucky

A majority of beef producers are very concerned about the cost of production. Losses due to preventable diseases such as parasitism are very important to address, especially in times of high feed costs. The question is often raised whether or not it makes economic sense to deworm adult beef cattle. Most adult animals have subclinical or undetectable symptoms from parasites yet there are still economic effects from parasitism due to multiple factors. Losses include the direct effects of reduced feed intake, reduced feed efficiency, and reduced milk production along with the indirect effects of immune system depression, decreased reproductive efficiency and poor calf growth. The most important effect on a production basis is appetite suppression followed by diarrhea and decreased immune response. These losses can affect all age groups of cattle but are more pronounced in the young, growing animals. In addition, the more efficient an animal is, the greater impact parasites can have on maintaining this efficiency. Parasitism is a condition of virtually all pastured cattle in Kentucky yet the level of harm can vary tremendously by farm, pasture, season of the year, stocking density, and the individual animal. The parasites themselves differ in their life cycles, their preferred host, the environmental conditions they enjoy, and damage they cause within the gut. The important nematodes or "roundworms" in the U.S. cattle population are Cooperia, Ostertagia, Haemonchus, Oesophagostomum, Nematodirus, and Trichostrongylus. Of these listed, Cooperia, Ostertagia, Haemonchus, and the fluke Fasciola hepatica are of the most concern because of the damage they cause in the digestive tract. Although many of today’s dewormers will effectively kill all of these worms, these parasites are not all actively transmitted at the same time. Therefore, treatment at a certain time of the year may completely kill one parasite and completely miss another one. For these reasons, it is important to understand what to use and when to use it.

The results of effective deworming are difficult to see and quantify in terms of dollars because we seldom leave a portion of the herd untreated with which to compare. University research, however, has documented improved animal performance from effective deworming in cow/calf operations including increased weaning weights and increased weaning rates (that includes both pregnancy rate and calf survival rate) in calves from treated cattle. A study performed at Iowa State University and published in 2006 examined 170 research trials evaluating pharmaceutical technologies in the cow-calf, stocker, and feedlot segments of beef production. These results were used to estimate the economic value of parasite control, growth promotant implants, antibiotics, ionophores, and beta agonists at the farm level in 2005.

Results for cow-calf are presented in the table:

In a nutshell, the larger the effect a technology has on production efficiency, the larger the effect it has on cost of production. If dewormers were removed, it would cost an average of $165.47 more per head to break even due to decreased weaning weight and rate and fewer calves sold to cover the costs of production. This was 2005 data and the cost is undoubtedly much higher in 2013. The message is clear that the more worms you have, the less cattle (in terms of weight and number) you have to sell. The best way to lessen the number of worms is to wisely use the most effective products available. Unfortunately, when it comes to choosing a dewormer, price and method of delivery (injectable, pour-on, or drench) are usually the driving factors rather than the product’s effectiveness.

There are basically two fundamental goals of effective parasite control in cattle. The first is protection of the host from disease and concurrent enhancement of performance. The second goal is to reduce contamination of the pasture by eliminating worm-egg shedding. These goals are accomplished by killing all stages of the roundworms including adults and larvae (L4, inhibited L4, and infective L3 stages) found inside the cattle. The timing of the deworming is very important; considerations include the season of the year, type of grazing programs practiced, and the overall management goals of the operation. Always work with your veterinarian to determine what will work best for your unique situation. Treat cattle at the recommended rate-this includes accurate animal weight, correct drug volume, and careful delivery of the product.

Basic recommendations for when to treat beef cattle for nematode or roundworm infections in Kentucky are as follows:

1. Spring treatment of cows – Deworming in the spring, especially cows that calve in the spring, significantly reduces pasture contamination and risk for parasitic problems in calves throughout the summer. Use of a macrocyclic lactone (Ivomec, Eprinex [including LongRange], Dectomax, or Cydectin) is encouraged because of the residual activity and the ability to kill both internal and external parasites. Use of generic ivermectin is not recommended due to widespread resistance to these formulations.
2. Summer treatment of the herd – Deworming in late June/early July is very effective because most of the worms are inside the cattle instead of on the pasture. Larvae do not survive hot, dry weather so many infective parasites in the environment die in the midsummer heat in Kentucky. Treating cows in the summer will effectively remove the larvae that hibernate in the stomach and damage the abomasal glands. Calves need deworming as they transition from an all milk diet to grazing grass and will typically benefit from deworming after they reach 6-8 weeks of age. Use of a macrocyclic lactone is encouraged for the same reasons stated above.
3. Fall deworming is not exceptionally important in adult cattle but is a necessity for young animals. Fall calving cows should be dewormed and/or cattle on heavily infected pastures due to overcrowded conditions or extended periods of moist, cool weather that encourages parasite survival. Deworming of young stock (weaned calves, replacement females, and yearling bulls) is important in the fall as animals less than 2 years old are much more susceptible to the deleterious effects of parasitism. In the fall, use of a benzamida zole or "white wormer" drench (Valbazen, Synanthic, or Safeguard) in conjunction with a pour-on for insect control is encouraged. The white wormers are exceptionally effective against Cooperia, the small intestinal worm that is very resistant to generic forms of ivermectin.

In summary, internal parasites can cause significant production losses in cattle, resulting in substantial economic losses. Although parasite damage is often subclinical or unnoticed, severe infestations can result in disease and death. Production losses from internal parasites include reduced milk production, reduced weaning weights, delayed puberty, decreased fertility and pregnancy rates, reduced feed intake, reduced feed efficiency and immune suppression in all classes of cattle. These losses are preventable with timely administration of effective dewormers.