As the days get shorter and nights colder, the important job of housing is arriving. Taking animals off pasture is the ideal time to rid the animal of parasitic infestations . Ruminants can pick up internal parasites only while grazing at pasture, because the encysted infective stages are located on the pastures and cannot survive on conserved forage. Thus when stock are housed, they can no longer pick up new infections until they are turned out onto grass the following spring. This means that effective anthelmentic l treatments at or during housing should clear parisitic problems until they return to pasture the next year. The year has been wet overall in many places providing ideal comditions for development of a number of parasites including stomach worms (Trichostrongylosis), lungworm or husk and liver fluke (Fascioliasis).
Trichostrongylosis (Ostertagiosis) is caused by a family of roundworm parasites. One of the most notable parasites in this group is Trichostrongylus ostertagii. These parasites cause Parasitic Gastroenteritis (PGE), of which there are two types. Type 1 PGE is caused directly by the presence of large numbers of roundworms within the intestine, each feeding on the intestinal lining, thereby depriving the bovine host of nutrients. Type 2 is caused by immature worms burrowing into the lining of the intestine and re-emerging in large numbers mid-winter. Type 1 PGE is the type most commonly encountered during the summer grazing season. These parasites typically develop from egg to adult within 21-28 days, in warm weather 21 days is more common.
Lungworm or Husk (Dictyocauliasis) is caused by a roundworm which effectively lodges itself within the windpipes of the bovine host. This leads to obstruction of the airways, along with collapse of the air sacs (known as alveoli) within the lung. It is not uncommon for bacterial or viral pneumonia to develop secondary to lungworm infestation. Lungworm is most commonly seen in young grazing stock which, cough when excited or roused. The duration of the life cycle of these worms is similar to that of the roundworms. However, part of the development is spent on pasture within a cyst-like structure, where the immature worm can quite easily overwinter. This allows the infestation to persist from one grazing season to the next.
Liver fluke (Fascioliasis) is caused by a specific flatworm, known as Fasciola hepatica. This parasite has a complicated life cycle that typically takes from 9-20 weeks to progress from beginning to end. Immature stages of the liver fluke are also able to survive in a cyst-like structure, similar to Dictyocaulus. The encysted fluke can survive in this state for up to 2 years. This has knock on effects for control measures as it means that once fluke is established, control programmes must be followed year-in, year-out.
All three of these classes of parasite can have a devastating economic effect on the cattle herd. A suitable treatment should be adapted for their control. It is advised to do this in conjunction with your local vet.
Padraig Hyland Is a large animal veterinary practionner and Technical advisory Vet with Bimeda, a Leading Veterinary Pharmaceutical Company.