The use of a gamma-type function to assess the relationship between the number of adult Teladorsagia circumcincta and total egg output

The relationship between faecal nematode egg count and the number of adult Telordasagia circumcincta was examined in 508 naturally infected lambs at 6 -7 months of age. The relationship was found to be convex and was empirical ly described by a gamma-type function of the form y = an(b) e(-cn), where n is the number of adult nematodes present and y is the number of nematode e ggs per gramme (epg) of faeces. This equation predicted that the peak expec ted egg count (277 epg) would occur at a worm burden of 2167 adult worms. T he absence of a linear relationship between egg counts and worm numbers is consistent with the existence of severe density-dependent constraints on th e fecundity of T. circumcincta.