The epidemiology of parasites is linked to environmental conditions in the region, influencing the development of eggs and infective larval stages, increasing the number of larvae in the period of higher humidity. Nematodiasis cattle in Ilam are major animal health problems, affecting an acute or chronic, damaging primarily to young animals, causing serious economic losses in livestock systems. In the Ilam province, 336 faecal samples of nursing calves were collected in the rainy period during 2004. This study aimed to determine the prevalence of Gastrointestinal Nematodes (GIN), the parasitic genus and the average load of eggs per gram of feces (Xepgf). The prevalence GIN was analyzed by the chisquared test and the average of larvaes per culture was analyzed with the analysis of variance using the Tukey’s test [11]. The prevalence of GIN in nursing calves was 78.27% that represented 263 positives animals. The Xepgf was 786.9 + 1195.58. There were no sex differences in the prevalence of GIN in nursing calves (P>0.05) 75.3% for males and 75.7% for females animals, both percents represented 116 and 146 positive animals respectively. Prevalence of larvae genus increased (P<0.05) for Haemonchus spp. and Cooperia spp. both with 85.71 and 71.42% respectively and decreased 52.38% for Oesophagostomum spp. and 38.09% for Trichostrogylus spp. It is concluded that the prevalence of GIN in the tropical region of Ilam during the rainy period is high, as well as the load of Xepgf and that the parasitics genus in the nursing calves are Haemonchus spp., Cooperia spp., Oesophagostomum spp. And Trichostrongylus spp.
