Factors affecting the prevalence of endoparasites in pre-weaning calves in a warm humid climate of Mexico

Parasitic diseases are a major challenge for livestock in warm climates, causing significant economic losses, particularly in young animals. Gastrointestinal nematodes (GIN) are highly prevalent, prompting us to investigate factors affecting the prevalence of endoparasites in pre-weaning calves in a warm, humid climate in Mexico. Fecal samples were analyzed to assess fecal egg count (FEC) dynamics and endoparasite prevalence. The prevalence of trematodes (<i>Fasciola hepatica</i> and paramphistomids) was determined on 12 beef cattle farms in the rainy season from May to September 2022 and July to November 2023. Nematode prevalence was monitored on four farms during 2022 and 2023. In addition, on one farm, the FEC was compared between dewormed and untreated groups. Coprocultures were conducted to obtain third-stage larvae for species identification based on morphology. The prevalence of <i>F. hepatica</i> was 12 % (77/640), while paramphistomids had a prevalence of 20.5 % (131/640). Trichostrongylids showed a prevalence exceeding 30 %, with maximum values reaching 93 %. The predominant species identified from coprocultures were <i>Cooperia</i> spp., <i>Oesophagostomum</i> spp., and <i>Haemonchu</i>s spp. Dewormed calves exhibited similar nematode eggs per gram of feces (EPG) to the untreated group, and nematode EPG in calves tended to decrease with age. In conclusion, age, sex, and farm management practices influence the prevalence of nematodes and trematodes. Nematode prevalence exceeded 30 % for most of the year, while trematode prevalence ranged from 12 % to 20 %.