The higher rate of infection with F. gigantica was observed in older animals which was similar to the reports of Rahman and Mondal (1983) in Bangladesh. It might be due to reduction of body resistance in older animals from debility as stated by Chowdhury (1993). The significant difference in the rate of infection between male and female animals as observed in this study apparently indicated that the female sheep were more susceptible to F. gigantica than male sheep. In this investigation S. indicum was found in 15.30% of the sheep whereas Islam (1969) recorded 10% S. indicum infection in sheep. During this investigations the highest occurrence (24.00%) was recorded during rainy season (July-October) while the lowest (8.57%) during summer season (March to June) but there was no available data to compare with it. The aged sheep from two years or above showed highest (45.56%) occurrence while the young animals aged less than two years showed lowest (2.17%) occurrence. This observation is closely related to the findings of Islam (1969) who reported that intestinal schistosomiasis was found 11.4% in 2 years aged sheep and 100% in 5 years aged sheep. The female sheep showed highest (36.89%) occurrence and the male showed the lowest (7.14%) occurrence.
The percentage of infection with amphistomes in sheep in Mymensingh was 61.14%. These findings is similar to that of Haq and Shaikh (1968) who reported that about 50-60% sheep and goats were infected with amphistomes as a mixed infection with other gastro-intestinal helminth parasites. Faecal examinations of cattle and buffaloes from some limited areas of Bangladesh have also suggested that the occurrence of amphistomes is much common in Bangladesh (Rahman and Mondal, 1983). Here also the female animals are relatively more susceptible to amphistome fluke infections than the males which are closely related to the report of Uddin (1999). The higher percentage of infection in the females may be due to the alteration in the physiological condition of the animals during pregnancy and lactation (production state) and also the lack of feed supplement in females for production, which may lead to the lowering of body resistance of the females. Amphistomes in sheep was higher in the monsoon and lower in the winter and summer season which is closely related to the reports of Uddin (1999).
M. expansa and M. benedeni occurred in 28.69% and 9.90% of the digestive system of sheep respectively examined during this survey experiment. The rate of infection by M. expansa as observed in this study is similar to the earlier reports of Haq (1967) in Bangladesh who recorded 31% in sheep and goats. Findings also conforms to the records by Vurusaner (1999) in Turkey who recorded 25% M. expansa infection in sheep. Higher rate of