Know your worms
Internal parasites in cattle can be divided into three broad groups: roundworms, flukes and tapeworms.
Parasitic adult roundworms live in various parts of the gastrointestinal tract of cattle. The most common roundworm in south-east Queensland is the Cooperia worm species (predominantly Cooperia punctata with smaller numbers of C. oncophora). These worms live in the small intestine and are often found together with Barber’s pole (Haemonchus placei) in the fourth stomach (abomasum) and the nodule worm (Oesophagostomum radiatum) in the large intestine. Barber’s pole and nodule worm are more pathogenic than the Cooperia spp. worms, and small numbers can produce heavy productivity losses.
Intestinal scour worms such as the Cooperia spp. worms and the nodule worms produce digestive disturbances, poor feed conversion, and scouring. Barber’s pole is a blood sucking worm that lacerates the abomasal wall as it feeds causing leakage of blood into the intestine, resulting in anaemia, protein loss, and failure to gain weight. Immunity to worms starts to develop at about 5 months of age and is fully expressed by about 18 months. This immunity can be compromised during periods of very wet weather and poor nutrition.
All these worms are prolific egg producers. Eggs passed out with the dung continue their development within the pat. If weather conditions are warm and moist, the resultant infective larvae move out of the pat and onto the pasture in a film of moisture. If weather conditions are drying, infective larvae can ‘wait’ protected in the pat for up to 18 months until the next rains provide enough moisture for the larvae to migrate onto pasture. The time from development of eggs to infective larvae can take from 4 to 21 days depending on the temperature and moisture conditions around the pat. Infective larvae can survive on pasture for about 3 months in summer and up to 6 months over winter. Very dry, windy conditions quickly kill infective larvae but many survive in the moist areas in grass around watering points. These surviving larvae are the source of re-infection.
During periods of warm wet weather, intake of large numbers of infective larvae during grazing results in explosive build-up in worm burdens often within a few weeks.
Conduct a worm test of young stock about four weeks after grazing commences and again at weaning. During very wet weather, another test at 10–18 months of age may be necessary.
Liver fluke (Fasciola hepatica) is often found in the Stanthorpe region and in the Mary River valley. Cattle grazing on irrigated pasture or green pick near water in summer are at risk of infection.
Adult flukes suck blood and in heavy infections can cause profound anaemia and reduced weight gains. Livers of infected cattle show varying degrees of fibrosis and grossly thickened bile ducts which may be calcified. Under normal conditions, clinical disease is only likely in young cattle; older cattle develop some immunity to infection.
Adult liver flukes inhabit the bile ducts of the liver and are prolific egg producers (up to 20,000 eggs per fluke per day). Eggs move with the bile through the small intestine and continue development in the dung pat. The resultant young, non-parasitic flukes continue their development in aquatic snails (Lymnaea spp) and when released from the snail encyst on partially submerged vegetation. Typically, flukey country is considered to be wet and low lying. Cysts ingested with the vegetation release young flukes in the small intestine. They migrate through the intestinal wall and through the liver and into the bile ducts where they mature into egg laying adults.
Occasionally, yearling cattle grazing in coastal areas can become infected with very large numbers of young fluke when grazing on partially submerged contaminated vegetation. The immature flukes damage the small intestine. Adult stomach flukes live in the first and second stomach and cause little damage.
Tapeworms live in the small intestine of calves and shed segments containing eggs into the dung. Immature tapeworms develop in a mite host and infect cattle when the mite is eaten with the graze. They cause no known pathogenic effects and calves rapidly become resistant to them.
Read more at Worm infestations: don’t guess.
Maxine Lyndal-Murphy, formerly Queensland Government.