Relationship between Sex and Age of Rabbits, Oryctolagus cuniculus (L.) and Infection with Nematodes Trichostrongylus retortaeformis and Graphidium strigosum

Abstract

Data on certain aspects of host-parasite relationships obtained from examination of the alimentary canals of 100 wild rabbits Oryctolagus cuniculus (L.) of known age, which were born and lived free in an experimental enclosure, have been analyzed statistically. The rabbits were infected with Trichostrongylus retortaeformis and Graphidium strigosum. There was a significant relation between the age of the host, and length and egg production of T. retortaeformis, worms recovered from young rabbits being longer and containing more eggs. However, the length of the worms was not related to the level of infestation for a constant age of host, neither was the level of infestation related to the age or sex of the host. In contrast to T. retortaeformis the length of G. strigosum was not related to the age of the host. Neither was there any relation between the length of worms and the level of infection. The level of infection with G. strigosum was found to be dependent on both age and sex of the rabbits. Younger and male rabbits were parasitized to a lesser extent. Counts of the thirdand fourth-stage larvae of G. strigosum in the lumen and wall of the stomach showed lower numbers in younger age groups. The epidemiology of nematode infections within free-living populations of the wild rabbit Oryctolagus cuniculus (L.) has been studied intensively by Bull (1953, 1956, and 1959) in New Zealand. In the course of his study he found that the age and sex of the host have an important influence on the incidence of nematodes Trichostrongylus retortaeformis, Graphidium strigosum, and protozoa Eimeria stiedae. However, due to the fact that there is no reliable method for the age estimation of rabbits it has not always been possible to analyze satisfactorily field data in relation to the age of the host. At Canberra, Australia, an opportunity to study the relationship between parasite infestation and age and sex of the rabbit was presented when at the termination of another study 100 rabbits of known age became available. Of the 100 rabbits, 99 were infected with T. retortaeformis and 79 with G. strigosum. The data collected from examination of their alimentary canals allowed a statistical analysis to be carried out on the relationship between size and egg production of parasites and the age of the host, and the level of infection in relation to the sex and age of the host. The results of this analysis are presented in this report. The stunting of worms and inhibition of egg production are generally regarded as manifestations of resistance of the host. A study of this phenomenon is also of some interest in evaluation of the accuracy of egg-counting as a technique for determination of level of infection with nematodes. MATERIALS AND METHODS