A comparison of the spring-rise phenomenon in the faecal nematode-egg counts of housed sheep with that of sheep grazing infective pasture.

Abstract Extract Among the various aspects of the seasonal fluctuations of worm egg counts of sheep investigated by research workers, the “spring-rise” phenomenon has aroused considerable interest and has focused attention on the role played by the ewe in trichostrongyle population dynamics. Studies on this phenomenon have been summarized by several workers (Crofton, 1954, 1958, 1963; Field et al., 1960; Soulsby, 1962; Spedding, 1962). The occurrence of a spring-rise in breeding ewes in New Zealand was recorded by Brunsdon (1964) who has also demon- strated the importance of the contamination deposited by the ewe at the time of the spring-rise, in affecting the speed and degree of build-up of trichostrongyle infestation in lambs (Brunsdon, 1966).