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 with the largest impact being the decrease in voluntary feed intake, followed by decreased absorption and digestion of critical nutrients. Immune function can also be compromised by the constant stimulation of parasitic infections.
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. In Kansas, most nematodes will go dormant during the winter months and 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 and will lay eggs that are passed through the digestive track and into the external environment via manure. It is important to note that not all cattle are affected by internal parasites the same. In general, calves are much more susceptible than mature cattle, and bulls are often more susceptible than cows. Even within each class of animal, infections are not evenly distributed. Maturity does play a key role in herd infection rates. Cows will develop decent immunity to internal parasites by about 4 years of age.
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. There are options when it comes to application including injectable, oral drench, feed additive, and pour-on 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.