AbstractA total of 179 wild rabbits were cage-trapped or shot from sites throughout N. Ireland. Each rabbit was dissected and the following parameters recorded; age of rabbit (defined by rabbit weight), sex of rabbit, reproductive state, infection with myxomatosis and liver weight. The liver, stomach, small intestine and large intestine were removed and examined for the presence of cestode, protozoan and nematode parasites. Parasites were identified and their burdens estimated.
The nematode parasites found were Graphidium strigoswn, Trichostrongylus retortaeformis and Passalurus ambiguus. The overall prevalence of G. strigosum was 92%, with a mean intensity of 362 ± 39, for T. retortaeformis it was 91% and 1439 ± 148 and for P. ambiguus it was 44% and 1077 ± 333. The frequency distributions of all three nematodes fitted the negative binomial probability distribution and were found to be aggregated. Both T. retortaeformis and P. ambiguus populations peaked in Quarter 3, but G. strigosum peaked in Quarter 4.
An analysis of variance was carried out relating nematode parasite burden to the age and sex of the rabbit, whether it was infected with myxomatosis and the Quarter of the year in which it was caught. Female rabbits were found to have significantly larger G. strigosum burdens than males (P<0.05). No significant relationship was found between the other two nematodes and host sex. There was a very highly significant relationship between rabbit age (P< 0.001) and G. strigosum burdens, with nematode numbers increasing from kittens to juveniles to adult rabbits. There was also a highly significant relationship between rabbit age and T. retortaeformis burdens (P< 0.01), with burdens decreasing from kittens to juveniles to adult rabbits. No significant relationship was found between rabbit age and P. ambiguus burdens. No significant relationship was found between infection with myxomatosis and nematode burden, but T. retortaeformis and P. ambiguus burdens tended to be higher in myxomatosis rabbits, lower in non-myxomatosis rabbits and lowest in recovered rabbits. The opposite trend occurred for G. strigosum.
Only 4% of rabbits were infected with cestodes, all of which were the species Mosgovoyia pectinata. No trematode parasites were found in the liver but 9.5% of the livers of rabbits were infected with the protozoan parasite, Eimeria stiedai. There was a very highly significant (P<0.001) increase in liver weight in rabbits infected with this parasite.
An external grass enclosure experiment was devised to test the effect of internal parasite burden on the growth rate of young wild rabbits. Due to the many problems encountered in this experiment, no rabbit growth data were obtained. However, five rabbit deaths in this experiment were positively identified as being due to severe E. stiedai infections, and 10 other fatalities occurred in which E. stiedai was the suspected cause of death. An internal experiment was also devised to test the effect of internal parasite burdens on the growth rates of young wild rabbits in a more controlled environment. In all, 40 rabbits were tested, 20 dosed with 0.2ml/kg of the anthelminthic Panacur, and 20 dosed with 0.2ml/kg water acted as controls. Rabbits were housed in rooms in groups of five and efforts were made to enrich their environment with the provision of an artificial “nest” and “tunnels”. No significant difference was found between the growth rates of rabbits treated with the anthelminthic and those treated with water.
|Date of Award||Dec 1997|
|Supervisor||Alan Bell (Supervisor)|