Source: Kansas State University
by A.J. Tarpoff, DVM, MS, beef extension veterinarian
Internal nematodes (or worms) have been and continue to be a major drain on beef cattle health and economic returns in the beef industry. Internal nematodes impact cattle performance in several different ways. The largest impact is the decrease in voluntary feed intake which is a physiological response due to changes in the abomasum, followed by decreased absorption and digestion of critical nutrients Immune function can also be compromised by the constant stimulation of parasitic infections. Economic losses of internal parasitism to the livestock industry have been estimated at over $3 billion annually. These losses are felt at the Cow/calf, stocker, and feedlot sectors of the industry.
Common cattle parasites are found naturally in pastures that cattle graze. The most important nematode species in cattle production are Ostertagia, Haemonchus, Trichostrongylus, and Cooperia. Cattle only become infected when they pick up infective L3 larvae as they graze. After eggs hatch in the environment, they molt or change forms twice to become the infective L3 state. Parasite eggs are very resilient and can survive in the environment for long periods of time. This includes surviving drought and winter conditions. This is also perpetuated by the adult nematodes going dormant inside the animal. This is known as hypobiosis. In Kansas, most nematodes will go dormant during the winter months, whereas in the southern United States they will go dormant in the hot dry summer months. This is a survival mechanism of the parasite. Once cattle graze infective L3 larvae, the larvae migrate to either the abomasum or intestinal track of cattle. This is where parasites continue their life cycle into adults. Adult parasites will lay eggs that are passed through the digestive track and into the external environment via manure. Worms can complete their life cycle in about 3 weeks. It is assumed that 90% of the total worm population is on the pasture.
It is important to note that not all cattle are affected by internal parasites the same. In general, calves are much more susceptible that mature cattle, and bulls are often more susceptible than cows. Even within each class of animal, infections are not evenly distributed. It is estimated that within a herd, 20% of cattle harbor 80% of internal parasite infections due to differences in immune status and other genetic factors. Maturity does play a key role in herd infection rates. Cows will develop decent immunity to internal parasites by about 4 years of age. These older animals will still harbor nematodes and shed eggs, but at a vastly decreased rate.
Treatment of internal parasites has numerous benefits to beef cattle production. Improved health, increased weaning weights, and increased fertility are all seen with proper parasite control. There are a multitude of de-worming (anthelmintic) products on the market. Most of today’s products fall within the Benzimidazole and the Macrocyclic Lactones classes. There are also options when it comes to application including injectable, oral drench, feed additive, and pour-on formulations. Many of the benzimidazoles would be referred to as “white wormers” or drenches, while Macrocyclic Lactones commonly are pour-on or injectable formulations. Some of these products are very short acting in the animal, while other formulations have longer acting residual effects. Regardless of product, anthelmintic resistant parasites are a real and increasing concern in the industry today. This means in some situations the products are no longer as effective as they once were. Prudent use of these therapies is critical to ensure their usefulness for years to come.
Discussing deworming programs with your veterinarian is a critically important conversation. Since every beef cattle operation is different, there are not cookie cutter parasite control programs that can be implemented. Working together with your local veterinarian under a Veterinary Client Patient Relationship will make sure the program fits the needs of the operation. The decisions on product selection and timing can vary depending on history, diagnostics (Fecal Egg Counts), grazing situation, stocking rate, time of year, class of animals, and regionality. For example, cattle entering a feedlot will typically only be dewormed on arrival because they will not be exposed to any more parasites since they are not grazing grass. While stocker calves on permanent pasture will be exposed continuously to parasites while they are grazing, so a different strategy would be implemented. Your veterinarian will also be able to give guidance on product purchasing decisions. Not all formulations are created equal. There are many generic products on the market today that may not have the same efficacy as others or the name-brand formulation. This is due to anthelmintics not having to prove what is called Bioequivalence, which most other generic pharmaceutical products such as antibiotics must prove.
There are some critical control points that every operation can do to limit the impact of internal parasites. One of the most important management pieces to implement is proper dosing of anthelmintic products. These products are dosed by weight. Underdosing can greatly increase the likelihood of resistant nematodes in the environment. Weigh scales on chutes can help with this. Grazing management is another critical component to parasite control. Nematode larvae typically do not migrate further than 5 cm up grass, and 20 cm horizontally from the manure pack. Over grazing grass too low to the ground will increase the opportunity for our animals to be exposed to nematodes. Lastly, ensuring adequate nutrition of our cattle, specifically protein, will enhance cattle’s immune response to internal parasites. While this does not clear parasite infections, it does lessen the impact of nematodes in many situations.
Internal nematodes negatively impact cattle operations each year. Understanding and combating the subclinical threat is very important. While overall management of internal parasites may look quite different between operations and regions, the planning all begins with a visit to your local veterinarian.
