Parasites in Livestock: What Producers Should Know

Parasites are one of the most common health challenges affecting livestock operations. From cattle and sheep to goats and swine, internal and external parasites can reduce performance, impact animal welfare, and cause significant economic losses if left unmanaged. Understanding how parasites affect livestock—and how to control them—is essential for maintaining a healthy herd or flock.

What Are Parasites?

Parasites are organisms that live on or inside a host animal and obtain nutrients at the host’s expense. In livestock, parasites are typically divided into two main categories:

Internal parasites (endoparasites) – These live inside the animal, commonly in the digestive tract, lungs, or blood. Examples include gastrointestinal worms, lungworms, and protozoa such as coccidia.

External parasites (ectoparasites) – These live on the surface of the animal and include pests such as lice, mites, flies, and ticks.

Both types of parasites can negatively affect livestock health and productivity. Heavy infestations may lead to poor growth, reduced feed efficiency, decreased reproductive performance, and increased susceptibility to disease.
(University of Kentucky Extension, 2023)

Common Internal Parasites in Livestock

Gastrointestinal worms are among the most significant internal parasites affecting grazing livestock. Animals become infected when they consume parasite larvae while grazing contaminated pasture.

Common internal parasites include:

• Roundworms (nematodes) such as Haemonchus contortus in sheep and goats

• Lungworms, which affect the respiratory system

• Tapeworms, which inhabit the digestive tract

• Coccidia, microscopic parasites that cause intestinal disease

Young animals are particularly vulnerable because their immune systems are still developing. Signs of heavy parasite burdens may include weight loss, diarrhea, poor hair or wool coat, anemia, and reduced growth rates. (Merck Veterinary Manual, 2023)

External Parasites and Their Impact

External parasites can also cause significant problems for livestock. Flies, lice, mites, and ticks can irritate animals and lead to decreased performance.

For example, flies can spread disease, disrupt feeding behavior, and cause stress in cattle and other livestock species. Lice and mites may cause itching, hair loss, and skin irritation, which can lead to secondary infections.

In addition to direct health effects, external parasites may reduce weight gain and milk production due to the stress they place on animals.
(Kansas State University Extension, 2022)

How Parasites Spread

Parasites spread through a variety of environmental and management factors. Pastures contaminated with parasite eggs or larvae are a primary source of infection for grazing animals.

Other contributing factors include:

• Overgrazed pastures

• Poor sanitation in housing areas

• High stocking density

• Warm and moist environmental conditions

• Introduction of new animals without proper quarantine

Because many parasite eggs and larvae can survive in the environment, proper pasture management and herd monitoring are important components of control.

Strategies for Parasite Control

Successful parasite management requires a comprehensive approach rather than relying on a single treatment method. Some of the most effective strategies include:

Strategic deworming
Working with a veterinarian to develop a targeted deworming program can help control parasite loads while reducing the risk of drug resistance.

Pasture management
Rotational grazing can help break parasite life cycles by allowing pastures time to rest and reduce contamination.

Good sanitation practices
Keeping housing areas clean and dry can help limit parasite survival and transmission.

Monitoring animal health
Regularly observing animals for signs of parasite infection allows producers to respond quickly before infestations become severe.

Integrated parasite management is increasingly recommended because overuse of deworming medications has led to growing resistance in some parasite populations.
(USDA Agricultural Research Service, 2023)

Protecting Livestock Health

Parasites are a natural part of livestock production, but effective management can minimize their impact. By combining good nutrition, strong biosecurity, proper pasture management, and strategic treatment programs, livestock producers can maintain healthier animals and improve overall productivity.

Sources

• Merck Veterinary Manual. Parasitic Diseases of Livestock.

• University of Kentucky Cooperative Extension. Internal Parasites of Livestock.

• Kansas State University Extension. External Parasites in Livestock.

• USDA Agricultural Research Service. Parasite Control in Livestock Systems.

• Penn State Extension. Managing Parasites in Grazing Livestock.