Stomach and intestinal worms

A broad range of stomach and intestinal parasites are described in this guide.

The life cycles of these parasites begin when cattle ingest infective-stage larvae with grass. Larvae penetrate the stomach or intestinal wall and mature to adulthood within the host. Adults produce eggs, which infect pastures through manure droppings. Eggs hatch into first-stage larvae and then develop to the third stage. Third-stage larvae migrate onto grass and are consumed by cattle. The duration of this life cycle is from five weeks to more than six months, depending on climate. Larvae survive winter temperatures in manure.

Brown stomach worms

The brown stomach worm, Ostertagia ostertagi, is the most common internal parasite of cattle. When grazing, cattle ingest third-stage larvae. Ingested larvae penetrate the gastric glands of the abomasal mucosa, producing nodules. Upon emerging from the gastrointestinal nodules, young adults severely damage the gastric glands and the digestive process. Affected animals suffer reduced appetite and weight loss.

In Type I infections, eggs begin appearing in the manure 18 to 60 days after larval ingestion. Calves from seven to 15 months of age are primarily affected. Effects are seen early in this period in temperate regions and late in the period in cool regions.

In Type II infections, unusual conditions, possibly climatic or nutritional, cause larvae to hibernate in the gastric glands up to six months. Severe damage can occur when these larvae are suddenly released. Type II infection occurs primarily in 12- to 20-month-old cattle. Effects are seen in late summer to autumn in warm-temperature regions and late winter to early spring in cold-weather regions.

Signs of brown stomach worm damage include diarrhea, poor appetite and weight loss. Edema (bottle jaw) may be seen in severe cases. Death may result from serious infections.


Several species of Cooperia parasites—primarily C. punctata, C. oncophora and C. pectincata—infect the small intestine of cattle. Cooperia is also called the small intestinal worm, and infections are found virtually everywhere cattle are raised. The life cycles of these species are similar to those of stomach worms. The period from ingestion of larvae to appearance of eggs in the feces is from 12 to 15 days.

Cooperia infections can impair weight gain. Heavy infections of C. punctata and C. Pectinata produce profuse diarrhea, loss of appetite and emaciation. The disease produced by C. oncophora is milder.


Hookworm infections, Bunostomum phlebotomum, occur primarily in Southern and Midwestern states but have been reported in many other areas. These worms are voracious tissue-eaters and bloodsuckers. Severe anemia can occur.

Hookworm larvae can enter the body by ingestion or through the skin. The larvae inhabit the small intestine. The period from ingestion to passage of eggs in the feces is 30 to 56 days.

Cattle infected by hookworms suffer appetite loss, weight loss and diarrhea.

Large stomach worms

The large stomach worm, Haemonchus placei, inhabits the abomasum, puncturing small blood vessels and feeding on blood. This worm is also called the barber-pole worm and wire worm. Relatively small numbers of these parasites in their fourth stage and adulthood can be damaging.

Signs of stomach worm infections are seen most frequently in young animals. However, older animals not previously exposed can be seriously affected. Affected animals suffer loss of appetite and severe anemia. Edema (bottle jaw) may be seen in highly severe cases.

Nodular worms

Larvae of nodular worms, or Oesophagostomum radiatum, penetrate primarily the wall of the lower small intestine. After five to 10 days, the larvae return to the lumen in their fourth stage of development. Pea-sized nodules are created by the damage of nodular worms. As with the brown stomach worm, the larva of nodular worms can be inhibited, delaying their return to the lumen. The period from ingestion to the appearance of eggs in feces is about six weeks.

Nodular worm infection in young cattle produces poor appetite; persistent dark, fetid and severe diarrhea; and weight loss. Severe infections may produce death. Older cattle suffer from reduced gut motility.


Tapeworm infections (Moniezia expansa, M. benedeni) affect young cattle. Eggs, which are shed by infected animals, are ingested by free-living oribatid mites. These mites live in soil and grass. After six weeks in the mites, eggs convert to an infective form, cysticercoids.

Cattle become infected by ingesting the mites. Eggs are again shed about five weeks after cattle ingest mites.

Thread-necked worms

Thread-necked worms, Nematodirus helvetianus, are found throughout the United States. They inhabit the upper one-third of the small intestine. Damage is created when the parasite tunnels into the intestinal mucosa, absorbing protein and blood.

Cattle suffering Nematodirus infection have rough hair coats. Other signs include poor appetite, diarrhea and weight loss. Economic effects are greatest in calves and yearling cattle.

Nematodirus eggs are highly resistant to environmental conditions. Eggs passed by cattle in one season may infect animals the following season.

The thread-necked worm may be missed when herds are surveyed for parasites. Females produce relatively few eggs. Authorities say that one egg per gram of fecal material indicates the need to deworm.


An intestinal parasite, the threadworm Strongyloides papillosus differs significantly in life cycle from the stomach worms described above. Males are not involved in the parasitic phase of the cycle. Females embed in the mucosa of the upper small intestine. Small, embryonated eggs are passed in the feces.

Calves are primarily affected by threadworm infection. Signs of infection, when apparent, include intermittent diarrhea and loss of appetite and weight. Sometimes threadworm infection produces blood and mucus in the feces.


Parasites causing trichostrongylus (Trichostrongylus axei, T. colubriformis) primarily inhabit the abomasum of cattle and the small intestine to a lesser degree. Damage is caused when larvae penetrate the gastro-intestinal mucosa, after which they emerge and mature within three weeks.

Young cattle are most susceptible to trichostrongylus, but infection also occurs in older cattle. Signs of trichostrongylus include poor appetite and watery diarrhea.


Infections caused by species of the Trichuris parasite (whip worms) affect primarily calves and yearlings. Trichuris eggs are very climate-tolerant and are likely to persist on problem premises.

The numbers of infective Trichuris worms are seldom large, and signs of disease are rarely seen. Thus, the effects of Trichuris infection are apt to be subclinical. In occasional heavy infections, dark feces, poor appetite and anemia may be seen.


Infections by lungworms, Dictyocalus viviparus, are seen most often in temperate climates. Larvae are ingested through grazing.

From the intestines, lungworm larvae migrate to the lungs via the lymphatic system and the arterial blood supply. Larvae emerge into the alveoli and migrate to the bronchioles and bronchi where they mature. The irritation caused by lungworms increases the secretion of fluids, which can lead to congestion or even emphysema and pneumonia.

Cattle of all ages can be affected. Older animals may acquire a degree of immunity from naturally occurring infections. Affected cattle show signs of lungworm disease ranging from moderate coughing to severe, persistent coughing. Some animals experience respiratory distress and even failure. Economic effects of this disease include weight loss and loss of milk production.

Liver flukes

Fluke disease in U.S. cattle is caused by the trematode Fasciola hepatica. F. hepatica eggs are passed in the feces of cattle. After hatching in water, the eggs infect lymnaeid snails, where development and multiplication occurs. After two months or longer, depending on temperature, an advanced stage of F. hepatica encyst on aquatic vegetation, from which they are ingested by cattle.

Following ingestion, young flukes are released in the duodenum, penetrate the intestinal wall and enter the peritoneal cavity. Then they penetrate the liver capsule and spend several weeks growing and destroying tissue before entering the bile ducts to mature and produce eggs. Two to three months usually elapse from ingestion to shedding of eggs in the feces. Most adult flukes are shed by cattle within five to six months.

When tissue damage occurs in the liver, adjacent clostridial spores may vegetate and release fatal toxins.

Control of liver flukes should include both repression of the snail population and treatment of susceptible animals.