Comparative epidemiology of gastrointestinal parasites in cattle and buffalo under smallholder systems in Thailand.

Gastrointestinal parasite (GIP) infections significantly limit livestock productivity in tropical smallholder systems, yet comparative epidemiological data between cattle and buffalo remain scarce. This study examined co-infection dynamics, parasite patterns, and risk factors in cattle and buffalo in Thailand. A cross-sectional study of 302 animals (30 farms) used fecal examinations to detect nematodes, rumen flukes, and Fasciola spp. Risk factors were assessed using univariable and multivariable logistic regression. Animal-level GIP prevalence was 69.54% (buffalo 78.07%; cattle 64.36%), with 100% herd-level positivity. The GIP infection in cattle was nematode-dominant (32.98%), while buffalo showed high rumen fluke (59.65%) and Fasciola spp. (22.81%) prevalence. Multivariable analysis for cattle identified grazing (aOR = 3.72, p = 0.020) and presence of other animals (aOR = 2.72, p = 0.011) as primary risks. In buffalo, young age (aOR = 0.23, p = 0.016) and male (aOR = 0.19, p = 0.005) were protective against rumen flukes, while shared grazing increased risk (aOR = 2.84, p = 0.039). Buffaloes frequently exhibited rumen fluke and Fasciola spp. co-infections, reflecting distinct host-specific dynamics. GIP epidemiology in cattle and buffalo within smallholder systems is shaped by interactions between environmental exposure, host characteristics, and parasite-specific transmission pathways. While nematode infections in cattle are primarily driven by pasture-based exposure, trematode infections in buffalo are closely linked to water-associated environments. These findings underscore the importance of adopting parasite-specific and species-adapted control strategies rather than uniform approaches.