Abstract
Background:
Gastrointestinal tract parasites (GIT) posed a significant economic constraints and public health challenges in the world including Pakistan.

Aim:
This study was carried out to assess the prevalence and associated risk factors effect on the prevalence of GIT parasites found in sheep of lower and higher altitudes of district Swat, Pakistan.

Methods:
Faecal samples from the rectum were collected randomly by means of gloved fingers and were then put in plastic bottles containing 70% ethanol. The collected faecal specimens were transported to parasitology laboratory of Malakand University in the Zoology Department, for the investigation of gastrointestinal parasites. The general laboratory techniques were applied to detect the parasitic infections.

Results:
Of the 300 faecal samples 90.4% (n=272/300) were found parasitized. The most prevalent species was Haemonchus spp 47.5% (n=191) followed by Trichuris spp 17.4%(n=70), Taenia spp 14.4% (n=58), Monezia spp 1.74%(n=7), Fasciola spp 1.49%(n=6), Eimeria spp 6.21%(n=25), Dicrocoelium spp 4.22%(n=17), Paramphistomum spp 4.67%(n=14), Nematodirus spp 2%(n=6), Filicollis spp 2.67% (n=8). Different risk factors such as gender, age, health status, grazing behavior, drinking water source, treatment, and nature of parasitism were investigated. Sex wise prevalence demonstrated that females were more parasitized than males. The association of helminth parasitic infection was noted statistically significant with mode of nutrition, body condition, age, altitudes and status of females (P<0.05). However, rate of prevalence of the infection was high in younger animals than older ones. The animals of higher altitudes were more infected than the animals of lower altitudes (P>0.05). In winter season the sheep were found more infected as 94.8% as compared to other seasons of the years (P>0.05). Number of eggs per gram for Haemonchus spp was 50-1600epg, Trichuris spp 50-300epg, Taenia spp 50-250epg, Fasciola spp 50-200epg, Monezia spp 50-150epg, Paramphistomum spp 100-150epg, Dicrocoelium 100-150epg, Filicollis spp 50-150epg, Eimeria spp (oocysts) 50-100epg, and Nematodirus spp 50-100epg, were detected.

Conclusions:
The current study evidenced higher helminth parasitic infection which can be prevented through ensuring antihelminthic treatments of the sheep population in different intervals.

Key words: Gastrointestinal parasites; Helminthiasis; Prevalence; Risk factors; sheep.