Gastrointestinal parasites in sheep and cattle: effect of the production system and seasonality in the Southwestern Iberian Peninsula

Spain is one of the main organic meats producing countries (sheep and beef), but these productions can be negatively affected by parasitic diseases which are influenced by environmental factors. This study aimed to evaluate the impact of the production system (conventional vs. organic) and the seasonality of sampling (cold vs. warm months) on the prevalence and parasitic burden of gastrointestinal parasites in sheep (n = 741) and cattle (n = 173). For this purpose, 10 farms in the southwest of the Iberian Peninsula (Spain and Portugal) with extensive production systems were analysed using McMaster technique in two climatic periods. The results indicate a higher prevalence and parasite burden in sheep compared to cattle (p < 0.05), with a special incidence of Eimeria spp. (73.1% vs 26%; 284.6 vs 138.6 OPG) and parasites of the order Strongylida (48.6% vs 25.4%; 95.1 vs 16.2 EPG). Organic systems showed a higher presence of Moniezia spp. (3.5% vs 1.4%), Trichuris spp. (3.9% vs 0.8%), and Dicrocoelium dendriticum (3.3% vs 0%) than conventional systems (p < 0.05). Furthermore, samples from warm months revealed a higher prevalence and parasite burden (p < 0.05), especially in the order Strongylida (60.6% vs 27.4%; 126.7 vs 32.5 EPG) and Nematodirus spp (5.6% vs 0.9%; 1.89 vs 0.22 EPG). These findings show that the type of production system and seasonality significantly influence parasite dynamics, with a more pronounced impact in organic systems during warm months.