Periparturient rise in faecal nematode egg counts in west African dwarf sheep in southern Ghana in the absence of arrested strongyle larvae

The nematode egg output of two groups of ewes, a pregnant test group (2-3 years of age) mated between March and April and a non-pregnant control group (5-6 years of age) was followed. The worm burdens acquired by worm-free 'tracer' lambs were also followed on the same pasture from March 1988 to February 1989. There was a significant difference (P less than 0.05) in the magnitude of the egg output in the test group compared with the control group. In the test ewes, an initial rise in egg production occurred 2 weeks after lambing and was maintained for five consecutive months. Necropsy worm counts from the 'tracer' lambs revealed that pasture larval levels were directly related to the levels of rainfall. Adult nematodes (Trichostrongylus colubriformis, Trichostrongylus axei, Haemonchus contortus, Oesophagostomum venulosum and Trichuris ovis), and some Moniezia expansa were present in almost all the lambs throughout the year, with the exception of January and February 1989. The absence of immature larvae in these lambs indicates that arrested development is not a feature of the life cycle of these species in Southern Ghana. The occurrence of a periparturient rise of nematode eggs in West African Dwarf ewes, a year-round breeder, means that susceptible lambs could be open to infection throughout the year. Control should, therefore, be conducted by treating ewes after lambing and restricting the breeding season to particular periods of the year.