Prevalence of O. columbianum (92%) was the highest but that of M. benedeni (2.66%) was the lowest (Table
1). Same type of experiment was carried out by Hassan (1964) who reported that 92.7% goats were positive to
Oesophagostomum spp. and 10.9% to Moniezia spp.infection. Qadir (1967) and Haq and Shaikh (1968) also
recorded the high prevalence of O. columbianum in goats in Mymensingh district throughout the year. The cause
of higher prevalence of O. columbianum can not be explained exactly but it can be assumed that bionomics of
this parasite may be associated with this matter. O. columbianum maintain direct life cycle in which third stage
larva (L 3 ) is infective stage. Goats become infected by the ingestion of these infective larvae with the
contaminated foodstuff during grazing. But these larvae are capable of free movements and can climb up on the
grass blades. They are positively hydrotropic and negatively phototropic. So, they are abundant on the grass
blades especially during the morning and in the evening (Soulsby, 1982). On the other hand, goats are habituated
in the eating of grass from the top level (Devendra, 1970). Therefore, chance of gaining infection with O.
columbianum in Black Bengal goat remains very high. Besides, in this study, viscera were collected from the
slaughterhouse. So, obviously almost all goats were adult. But infection with Moniezia spp. usually occurs in
young goats (Soulsby, 1982). This sampling error might have an effect on the prevalence of Moniezia spp.
during the present study. However, utmost attempts were made to minimize this sampling error during sample
collection.