The use of pregnant mares to investigate the pathophysiology of EAFL is expensive both in the acquisition and maintenance of the mares and progress is slow due to their length of gestation.Therefore, an animal model with a short gestation is required for cost efficiency and to increase the rate of research. In the studies described here the guinea pig (GP) is investigated as a potential animal model as its gastrointestinal tract is anatomically and physiologically similar to that of the horse. The disadvantage of the GP is that it has a different type of placentation to the horse. The objectives of the present studies are to confirm that the GP is a suitable model for EAFL and to investigate the microbiological and histopathological outcomes of pregnancies over time following exposure to PC.In the initial experiment, the objective was to determine if the oral administration of PC causes abortion in the guinea pig. Fifteen pregnant guinea pigs were allocated into a treatment group (n=9) and a control group (n=6). The treatment group received a capsule containing 0.2g/kg (n=6) daily for 3d from day 35 of gestation (GD35) or 1g/kg (n=3) macerated whole processionary caterpillar daily for 3d from GD26. The matching control guinea pigs were administered capsules containing commercial guinea pig pellets daily for 3d. All guinea pigs were monitored daily until 3d prior to term when they were moved into a separate pen for delivery. After delivery, the number of offspring and any gross abnormalities were recorded. One GP aborted. All other GPs delivered healthy offspring at term. The guinea pig that aborted had received the higher dose of PC (1g/kg) ii and was treated for 3d from GD26. No fetal tissues were retrieved. The mother was euthanased and samples for microbiological examination were taken from the peritoneal cavity, uterus and heart blood. Bacteria were isolated from the uterus and were similar enteric and environmental organisms to those isolated from the EAFL experiments. Histopathology was performed on lung, liver, heart, gastrointestinal tract and uterus. The results showed that PC setae and setal fragments were found throughout all tissues.Based on the findings of the first experiment, the objective of the second experiment was to confirm that abortion could be induced by administering PC to guinea pigs at GD25. Eight guinea pigs were used in the treatment group and four in the control group. The treatment group received PC exoskeleton and integument on 5 consecutive days from GD25. The control group did not receive any PC components. Pregnancies were monitored daily by trans-abdominal ultrasound. If fetal death was observed by ultrasound (n=2; GD31, 55) the guinea pigs were anaesthetised and sampled.If fetal death was not detected the guinea pig was anaesthetized and sampled at a set time point from the first day of treatment (n=6, GD26, 29, 40, 45, 50, 60). The control guinea pigs were also sampled (n=4, GD29, 40, 50, 60). Samples collected for microbiological examination were taken from the peritoneal ca...