BACKGROUND: In Nepal, cows and buffaloes are common livestock used in subsistence farming and are often afflicted by helminth and protozoan parasites. OBJECTIVES: This study aimed to evaluate the prevalence of intestinal parasitic infections (IPIs) and contributing (i.e., previously suggested to be associated with IPIs) factors affecting bovine calves in the Birgunj region, Nepal. METHODS: From June to December 2023, 200 faecal samples (100 from commercial farms and 100 from subsistence farms) were collected and analysed using flotation and sedimentation techniques. Contributing factors were systematically obtained using structured questionnaires and direct field observations. RESULTS: Overall, 62% of the samples contained oocysts or eggs of intestinal parasites. The identified species included one protozoan (Eimeria spp., 7.5%), five nematodes (Strongyloides spp., 15.5%
Ostertagia spp., 6.5%
Haemonchus spp., 4.5%
Toxocara spp. and 11.5%
Ascaris spp., 4%) and two trematodes (Fasciola spp., 20%
Paramphistomum spp., 13%). The Fasciola spp. prevalence was notably higher in calves from subsistence farms compared to commercial farms (p = 0.015). Buffalo calves presented higher rates of Fasciola spp. and dual infections (p = 0.001), whereas cow calves presented a greater prevalence of Toxocara spp. (p = 0.046). Calves grazing near riverbanks presented significantly higher odds (adjusted odds ratio [aOR]: 2.76, 95% confidence interval (CI) [1.07-7.14]) of any IPIs, even after adjusting for other significant factors in a bivariate model. Factors, such as free-range rearing, subsistence farming and grazing on riverbank grasses, were linked to higher odds of Fasciola spp. infection in the bivariate model, but only the presence of buffalo calves ([aOR]: 2.64, 95% CI [1.03-6.76]) remained significant after mutual adjustment (i.e., in the multivariate model). CONCLUSIONS: These findings underscore the significant burden of intestinal parasites in young calves, highlighting the need for regular inspections and preventive measures.