Seasonal variation in the effects of Mediterranean plant extracts on the exsheathment kinetics of goat gastrointestinal nematode larvae

• Seasonal pattern for inhibition of larval exsheathment by the ethanolic extracts was observed.
• P. lentiscus and I. viscosa with peaks of inhibition during fall and spring, but not in P. latifolia.
• Peaks of exsheathment inhibition were associated with seasonal peaks of phenolics contents.
• Not all the seasonal variation could be related to the content of phenolics in plants.
• Seasonal variation in anthelmintic activity should be taken into account.

The use of chemical drugs for the control of Gastrointestinal nematodes (GINs) causes rapid development of resistance to anthelmintics in worm populations. The possible use of bioactive ingredients from plants has been identified as a valuable solution to modulate the biology of parasitic nematodes and consequently to counteract the negative effects in the hosts. However, the concentration of these bio-actives in anthelmintic plants can be seasonal and we hypothesized that this may cause different anthelmintic bio-activity. Using a two-species but steady population of parasitic nematodes (ca. 20% Teladorsagia circumcinta and 80% Trichostrongylus colubriformis), we tested this hypothesis by using the larval exsheathment inhibition assay (LEIA). We examined effect on L3 larval exsheathment kinetics and the polyphenol content of ethanol 70% extracts of Pistacia lentiscus, Phillyrea latifolia, and Inula viscosa clipped on December (winter), May (spring), June (summer), and September (fall). Extract concentrations in assays were 600, 900, 1200, and 2400 ppm. Extracts obtained from P. latifolia showed similar inhibition of larval exsheathment throughout the year; in contrast, the inhibition by both extracts of P. lentiscus and I. viscosa was affected by season, ranking fall > summer > spring = winter and spring > summer = fall > winter, respectively. The total polyphenol content in foliage of the three plant species was highest in the fall for P. lentiscus and in spring for I. viscosa, but did not vary significantly for P. latifolia. Differences in larval exsheathment inhibition did not completely fit differences in phenolics contents. Seasonal variation in anthelmintic activity should be taken into account where plants are integrated into anthelmintic strategies.