Abstract Infections with gastrointestinal (GI) nematodes severely affect small ruminant health and compromise their productivity and reproductive performances and can be a major cause of economic losses in small ruminant production. High burden of infections with nematodes may lead to death; and under field conditions, most infections are usually mixed consisting of different species of nematodes. Sheep and goats are infected with gastrointestinal nematodes while grazing and the biology of the infective larvae on the pastures is important in planning effective control programs. In general, the development of the free-living stages of gastrointestinal nematodes is largely dependent on temperature, with development rate increasing at warmer temperatures, while moisture is also required for the development cycle to proceed. Temperature also influences grass growth and hence exposure independently of larval development and survival. East Azerbaijan province in terms of livestock animal population in particular sheep breeding is one of the most important provinces of Iran and due to the amount of rainfall is susceptible to worm’s contamination in livestock animal. In this survey, fecal samples of 5934 sheep in 19 cities in East Azerbaijan, from 2002-2009 were examined by the Clayton-Lane method. Briefly, a sample of feces, 1-5 g, was well mixed with water (about 30-50 ml) and strained through a sieve (1 mm mesh) to remove coarse fecal material. The mixture was sedimented for 10-15 minutes on the bench, or by light centrifugation for two or three occasions, until the supernatant was clear. The sediment was then mixed with a saturated solution of sugar in a centrifuge tube (15 ml volume) and centrifuged for one or two minutes at 500 g. The egg floated and coverslips were placed on the tubes in centrifuge and after 5 min the samples were examined for the presence of eggs at 100x and 400x magnifications under the light microscope and the number eggs of Nematodirus, Marshallagia, Trichuris, unknown nematodes parasite eggs and the whole of the nematode eggs were determined in these cities by their shape and size. These data were analyzed by the SAS software. The results showed that the Kaleibar was the most infested city and the Malekan had the lowest contamination to gastrointestinal nematode parasites. Marshallagia and Trichuris had the maximum and minimum quantities of means with 11.12±32.02 and 2.23±13.78, respectively. A study on the correlation between humidity in the second month and humidity average and fecal egg count showed that there is a positive and significant (p < 0.01) correlation between them. Base on the results of this survey high humidity in regions and seasons are risk factors for propagating worm infestations and distinct handlings are necessary for preventing the mentioned phenomenon. This study survey on geographical situation in 19 cities of East-Azerbaijan indicated that the infestation rate to gastrointestinal nematodes in south of province (Malkan city) is at the minimum rate and in north province (Kaleibar city) is in maximum rate. Because the north region of East-Azerbaijan province is warmer and moister from the other regions, the high rate of infestation to GI nematodes was expected. Furthermore, differences in the population of livestock animals in the two regions are important in the rate of infestation to nematodes. In conclusion, the results of the study denoted that even approve the anthelminthic drugs in the livestock animals, the rate of infestation to GI nematodes is high. Also, the results of this survey are showed that a positive correlation is between EPG and the mean of humidity and this is important that treatment and prophylaxis are needed to decrease the risk of the disease. This research serves as a baseline for future studies on prognosis and prophylaxis of GI nematodes. These regional differences appeared to be systematic and can be ascribed to differences in applied pasture management and climatic conditions, and cause a need for regionally adapted monitoring and control systems. Keywords: Sheep, Nematode, EPG, Correlation, Humidity. Infections with gastrointestinal (GI) nematodes severely affect small ruminant health and compromise their productivity and reproductive performances and can be a major cause of economic losses in small ruminant production. High burden of infections with nematodes may lead to death; and under field conditions, most infections are usually mixed consisting of different species of nematodes. Sheep and goats are infected with gastrointestinal nematodes while grazing and the biology of the infective larvae on the pastures is important in planning effective control programs. In general, the development of the free-living stages of gastrointestinal nematodes is largely dependent on temperature, with development rate increasing at warmer temperatures, while moisture is also required for the development cycle to proceed. Temperature also influences grass growth and hence exposure independently of larval development and survival. East Azerbaijan province in terms of livestock animal population in particular sheep breeding is one of the most important provinces of Iran and due to the amount of rainfall is susceptible to worm’s contamination in livestock animal. In this survey, fecal samples of 5934 sheep in 19 cities in East Azerbaijan, from 2002-2009 were examined by the Clayton-Lane method. Briefly, a sample of feces, 1-5 g, was well mixed with water (about 30-50 ml) and strained through a sieve (1 mm mesh) to remove coarse fecal material. The mixture was sedimented for 10-15 minutes on the bench, or by light centrifugation for two or three occasions, until the supernatant was clear. The sediment was then mixed with a saturated solution of sugar in a centrifuge tube (15 ml volume) and centrifuged for one or two minutes at 500 g. The egg floated and coverslips were placed on the tubes in centrifuge and after 5 min the samples were examined for the presence of eggs at 100x and 400x magnifications under the light microscope and the number eggs of Nematodirus, Marshallagia, Trichuris, unknown nematodes parasite eggs and the whole of the nematode eggs were determined in these cities by their shape and size. These data were analyzed by the SAS software. The results showed that the Kaleibar was the most infested city and the Malekan had the
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