Roundworms (nematodes) are important endoparasites, causing clinical disease and lost production in young sheep.
Most roundworms follow a similar life cycle.
Parasitic gastroenteritis (PGE)
Roundworm control is inevitably complex. Exposure of naïve animals to infective L3 larvae on pasture can be minimised:
by finishing lambs quickly, before the challenge becomes production limiting;
by grazing susceptible sheep only on ‘safe’ pasture, thereby evading an infective L3 challenge;
or by using anthelmintic drugs to suppress pasture larval contamination.
Effective pharmaceutical drugs are, and will always be, essential for the treatment of clinical cases of PGE. The major gastrointestinal nematode parasites (worms) of UK sheep are the trichostrongyle worms:
Teladorsagia (formerly Ostertagia) circumcincta the ‘brown stomach worm’, found in the abomasum
Trichostrongylus vitrinus (or Trichostrongylus colubriformis in southern Britain) the ‘black scour worm’ found in the proximal small intestine
Haemonchus contortus (the ‘barber’s pole worm’)