CONICET | Buscador de Institutos y Recursos Humanos

Nematode strongyles are usually present in grazing horses. A control parasite program was carried out in a horse reproductive center in Argentina (Doña Pilar Embriones, Lincoln, Buenos Aires). The objective of the present work was to evaluate the effect of nematode infection on reproductive performance of mares (donor and recipient) and stallions. Individual EPG were performed to 616 mares (73 donors and 543 recipients) and 38 stallions at least 2 times during the breeding season. Data from 471 flushings and 426 embryo transferences were analyzed. In fecal samples, small strongyle eggs were mostly prevalent, with sporadic appearance of big strongyles and tapeworms. Mares were classified in two groups accordingly to EPG counts: group with low parasite burden (L): EPG < 100 in all samples and group with high parasite burden (H) EPG >= 300 in at least one sample. Donor L mares had higher rate of positive flushings (P = 0.013) and more embryos per flushing (P = 0.032) than donor H mares. Transferred embryo from L donor mares resulted in similar pregnancy rates than embryo from H donor mares. Pregnancy rate was unaffected by parasite egg presence in recipient mares. Stallions were classified in three groups accordingly to EPG levels: low (L) EPG < 100, medium (M) 100 >= EPG <500 and high EPG>= 500. Positive flushing rates were negatively affected by increasing stallion EPG level (P = 0.016); whereas number of embryos and pregnancy rates remained unaffected. In conclusion small strongyle infection impaired reproductive performance in horses under embryo transfer program in early stages (until embryo recovery), whereas subsequent phases of transference and pregnancy rates were not modified by parasite burden.