Health & Husbandry
Green grass and parasite control go hand in hand.
February 24, 2025
Grass never looks quite so green and beautiful as those first blades popping up in the spring. Maybe it is the contrast of bright green surrounded by brown, dormant forage. Maybe it is the knowledge that new grass is on the way, signaling winter is nearing an end. Regardless, green in the grazing pasture can certainly raise your spirits.
The coming of spring means cows are gearing up to do what they do best: transform sunlight into beef using grass as fuel. Internal parasites can put a kink in this process by decreasing feed efficiency, but a good parasite control program can help manage this challenge. Designing a strategic parasite control program includes understanding the parasite’s life cycle, knowing which animals are most susceptible and matching parasite burden with appropriate control.
Parasite life cycle
Several internal parasites can be a concern to cattle, and this discussion focuses on roundworms. These worms belong to a class of parasites that infest the gastrointestinal tract of cattle. There are several common types of roundworms (sometimes called strongyles) that infect cattle, including Ostertagia ostertagi, Haemonchus placei, Trichostrongylus species and Cooperia species.
Although several different species are present, many share similar life cycles. Adult roundworms live in the gastrointestinal tract of infested cattle and shed eggs in cattle feces. These eggs hatch into larvae, which develop and migrate to areas of forage to be consumed by cattle. Once cattle ingest larvae, the process starts again as larval stages develop into adult parasites and begin shedding eggs.
Forage and grazing are important components of the parasite life cycle as consumption of larvae is necessary for new infestations or reinfestations to occur.
One parasite (Ostertagia ostertagi) has an important variation in its life cycle. This parasite can go through the same life cycle as other parasites, or it can go into a dormant state (called hypobiosis) where the larvae encyst in the abomasum waiting for a more opportune time to reproduce.
Environmental conditions can influence when this occurs. For example, in the winter in northern climates and the summer in southern climates the environment is inhospitable for egg survival, leading to potential hypobiosis by Ostertagia. There are a few challenges with this process, including parasite control, as not all dewormers will kill encysted (hypobiotic) Ostertagia and when the new season comes, a reemergence can cause clinical symptoms in cattle. Understanding the life cycle of common internal parasites can help identify strategies to effectively control infestations.
Internal parasites can limit feed efficiency in cattle, and a strategic parasite control program should be designed for each operation.
Susceptible animals
Not all cattle are equally susceptible to parasite infestations. While there are some genetic differences, there are also differences in ages of cattle, with calves being more susceptible to issues with parasites than adult cattle. Some of this difference may be related to previous exposure and a level of immunity, but part of the difference may also be related to the fact young growing cattle require a higher plane of nutrition, and reductions in feed efficiency may be more apparent in this type of cattle.
In addition to cattle type, environment and climate also influence the likelihood of parasite infestations. As noted in the parasite life cycle, the method of infestation is grazing forage infested with parasitic larvae: Cattle need to be grazing and the larvae need to be able to survive. While these larvae can be fairly hardy, they tend to thrive in areas with relatively warm weather and high moisture. All areas of the country can be affected by parasitism but not to the same degree.
Cattle affected by parasitism may show signs of thin body condition, long and rough hair coat, and — in extreme cases — bottle jaw. Bottle jaw is swelling or fluid buildup below the lower jaw and a symptom caused by severe loss of protein to parasites (the protein level in the blood is so low that fluid is leaking from the vessels and pooling, with the most noticeable area being below the jaw).
Symptoms do not need to be this dramatic to warrant treatment, and assessing the level of parasitism in the herd may be an appropriate step to determine the strategic parasite control program.
Assessing parasite burden, control needs
Talk to your veterinarian to determine the best strategic internal parasite control program for your operation. Local knowledge is important in selecting not only the appropriate product to utilize for your class of cattle, but also the timing and frequency of administration.
Your veterinarian may recommend some testing to more accurately determine the level of parasite burden. These tests often involve fecal examinations on a subset of cattle and may include a quantitative evaluation to determine both the number of fecal eggs and the type of roundworms present. This information can be valuable in designing a strategic parasite control program.
Conclusions
Internal parasites can limit feed efficiency in cattle, and a strategic parasite control program should be designed for each operation. The life cycle of the internal gastrointestinal parasites relies on grazing for reinfection; therefore grazing seasons are a good time to discuss appropriate control techniques.
Calves are more susceptible to parasitism than cows, and the level of effect on the herd often depends on region of the country.
Discuss a parasite assessment plan and a strategic control program with your veterinarian to come up with the best solutions for your herd.
Editor’s note: Author Brad White is on faculty at Kansas State University College of Veterinary Medicine and serves as director of the Beef Cattle Institute. To learn more on this and other beef herd health topics, tune in to the weekly Beef Cattle Institute Cattle Chat and Bovine Science with BCI podcasts available on iTunes, GooglePlay or directly from www.ksubci.org.
Related Content
Current Angus Beef Bulletin
The April issue has a “Focus On Females,” including a special advertising section devoted to herds intent on providing the female foundation.
