The spring-rise phenomenon: The relationship between the time of lambing and the commencement of the rise in faecal worm-egg counts

Abstract

Abstract Extract The greatest weight of evidence to date supports the view that the spring-rise in faecal worm-egg counts of sheep is due to the simultaneous maturation of latent over-wintering larvae, initiated by the depression of the immune status of the host (Spedding and Brown, 1956; Field et al., 1960; Soulsby, 1962; Gibbs, 1964). The phenomenon may be enhanced by stress factors such as parturition (Crofton, 1954) and severe climate and malnutrition (Paver et al., (1955). Crofton (1954) concluded that the rise in egg counts occurring in ewe flocks in spring was related to the time of lambing. He found that the rise in individuals occurred about six to eight weeks after parturition and was normally of short duration. While the mean time of the increased egg count of each individual was about two weeks, the increased egg count in the flock was spread over a period equivalent to the length of the lambing period. In a later paper, Crofton (1958) described a similar post-parturient rise in autumn-lambing...