The signs shown below can also be associated with diseases other than worm infections. If animals showing any of the signs below do not improve within 5-7 days after treatment with a known effective drench, you should seek veterinary advice, as they may be due to another cause. Animals with a very severe worm infection may not recover despite treatment with an effective drench, if the infection is too far advanced.
Dairy calves, and beef calves in the several months after weaning, are most at risk of worm infection. While cattle older than 18 months of age have some resistance to worm (but not liver fluke infections), they may be vulnerable, especially if close to parturition, or nutritionally stressed. Bulls are generally more susceptible to internal parasite infection than cows. For more detail see the section on which animals are susceptible to worms.
Death due to worm infections is uncommon in cattle, and rarely occurs rapidly. For small brown stomach worm (Ostertagia ostertagi) and small intestinal worm (Cooperia species) infections, death is usually preceded by scouring (diarrhoea) and weight loss in many of the affected herd. With barber's pole worm (Haemonchus placei) infections, animals show no signs until heavy worm burdens develop and deaths eventually occur, although examination of affected animals in the preceding days would have shown severe anaemia.
Infections of small brown stomach worm (Ostertagia ostertagi) and small intestinal worm (Cooperia species) are often mixed and result in a decrease in appetite, damage to the gut lining and reduced metabolic efficiency. As a result, affected animals lose weight and body condition or growth rates are reduced, and with severe infections some may become emaciated and even die. Smaller worm burdens result in less muscle (meat) growth, and lower milk production.
Liver fluke infection in cattle is usually chronic and can cause a loss of appetite.
Weight loss due to barber's pole worm (Haemonchus placei) infections may result in animals failing to meet target weights.
Swelling under the jaw results from both severe barber's pole worm (Haemonchus placei) and liver fluke infections. The loss of blood results in anaemia and less protein in the blood. This imbalance in the normal body fluids results in fluid accumulating under the jaw in some, but not all, affected animals. However, it is not a reliable sign as it does not always occur during outbreaks of barber’s pole worm disease and can be caused by other factors (e.g. a severe lack of protein in under-nourished calves).
Although not common, abdominal swelling due to fluid can occur as a result of liver damage associated with liver fluke. Like bottle-jaw, it is the result of low protein in the blood causing body fluids to be out of balance and fluid builds up in the abdominal cavity.
Animals experiencing abdominal pain may stand with the back humped up. This can occur with acute liver fluke infection but is not common. It is associated with young fluke migrating through and damaging the liver and is also frequently seen with nodule worm (Oesophagostomum radiatum). The same behaviour may also be observed in conjunction with foul-smelling scours and weight loss as a result of coccidiosis.
Lungworms (Dictyocaulus viviparus) infect the airways of cattle, preventing airflow and causing the production of frothy mucus that may cause the animal to cough and there may also be nasal discharge. In heavy infections, pneumonia (inflammation and infection in the lung tissue) may be evident, accompanied by rapid breathing.
Barber’s pole worm (Haemonchus placei) is the only roundworm to cause anaemia (blood loss) as it sucks blood from the lining of the fourth stomach (abomasum). Feeding by fourth stage larvae and adults may remove 0.05 ml of blood per worm. A burden of 1000 worms (seen as a worm egg count of about 500 epg) may remove 50 ml of blood per day from the host.
Liver fluke also cause anaemia. The adult flukes localise in the bile ducts and damage blood vessels so they can feed on the blood.
Severe acute or ongoing (chronic) blood loss from either barber’s pole worm or liver fluke feeding leads to obvious signs of anaemia, seen as pale gums, conjunctiva (inside the eyelids) and vulva. The resulting reduction in oxygen availability causes a lack of stamina, seen as lagging or collapse on exertion, and ultimately death.
Lethargy or weakness can result from a severe infection of many worms. With small brown stomach worm (Ostertagia ostertagi) and small intestinal worm (Cooperia species) infections it is (rarely) associated with lack of energy and exhaustion, secondary to weight loss and decreased appetite. With barber's pole worm (Haemonchus placei) infections it is due to anaemia and the lack of red blood cells to carry the oxygen required for muscle function. In either case, lethargy is most apparent when individuals or a number of individuals or groups fall behind the others when mustered. Although fairly rare in cattle, they may collapse and there is a risk of death if they continue to be pushed along or are otherwise stressed.
The presence of small brown stomach worm (Ostertagia ostertagi) and small intestinal worm (Cooperia species) can initiate a strong immune response from the host animal that causes inflammation of the lining of the gut resulting in diarrhoea (scouring). Scouring results in a loss of protein from the gut and lowered absorption of nutrients, exacerbating weight loss and reducing growth rates. With severe infections young animals can become emaciated and die.
Inflammation due to severe small brown stomach worm (Ostertagia ostertagi) infections causes the lining of the abomasum to become thickened, with small white crater-like nodules replacing damaged acid-producing glands. This leads to an increased permeability of the gut and consequent diarrhoea.
Severe cases of stomach hair worm (Trichostrongylus axei) in the abomasum may produce a gastritis (inflammation) with congestion and ringworm-like lesions. Small intestinal worms (Cooperia species) in the small intestine cause inflammation, patchy death of tissue and bleeding.
Nodule worm (Oesophagostomum radiatum): The larvae of nodule worms migrate through the walls of both the small and large intestines as they develop to the fourth and then adult stages. Small gritty lesions form around larvae in the wall of the small intestine, and larger lesions with soft centres form in the wall of the large intestine. Larvae can sometimes migrate to other tissues, including the lung, liver and lymph nodes, causing nodules in these.
Small brown stomach worm (Ostertagia ostertagi): Swellings are also evident in the fourth stomach (abomasum) of cattle severely affected by small brown stomach worm. Larvae entering the gastric glands produce small white crater-like nodules which merge together to give the mucosa a ‘morocco leather’ appearance.
This is a yellow colour of the mucous membranes (gums, vulva and conjunctiva) and the skin resulting from damage to the liver. Higher than normal levels of bilirubin (a waste product from the liver) accumulate in the blood stream. The colouring results from the yellow pigment found in bilirubin.
Jaundice occurs with liver fluke, due to increased red blood cell breakdown and damage to the bile ducts by the fluke.