Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 2011
Publication Date: March 9, 2011
Citation: Foster, J.G., Cassida, K.A., Turner, K.E. 2011. In vitro analysis of the anthelmintic activity of forage chicory (Cichorium intybus L.) sesquiterpene lactones against a predominatly Haemonchus contortus egg population. Veterinary Parasitology. 180(3-4):298-306. Interpretive Summary: Barber pole worm infections in sheep and goats are responsible for significant production losses and animal deaths annually. Over the past several decades, dewormers have been used extensively to control this gastrointestinal parasite. For many producers, these pharmaceutical drugs are no longer a viable option because the parasite has developed resistance to many or all of them. Supplemental approaches for parasite control are therefore critical to the survival of the small ruminant industry. Dual purpose forages that can provide both nutrients and anthelmintic natural products to grazing livestock are now considered essential components of parasite control strategies. Small ruminants with gastrointestinal parasite burdens have performed better when grazing chicory pastures, and anthelmintic activity of the herbage has been attributed to chemicals called sesquiterpene lactones. Forage chicory cultivars have different proportions of three specific compounds of this type, so we conducted laboratory studies with representative extracts of two chemically distinct cultivars to determine whether the compounds have different effects on barber pole worm eggs. One of the compounds was much less effective than another in inhibiting egg hatching. Results suggest that chicory plants with a high concentration of the more effective compound would be preferable in small ruminant pastures, and they provide a basis for selecting among available cultivars for grazing applications and for developing a new chicory cultivar with improved anthelmintic potential. These decision support tools will help ensure long-term economic viability for sheep and goat producers and availability of small ruminant meat products for consumers.
Technical Abstract: The anthelmintic activity of chicory (Cichorium intybus L.) herbage has been attributed to sesquiterpene lactones. Chicory leaves contain significant amounts of lactucin (LAC), 8-deoxylactucin (DOL), and lactucopicrin (LPIC), but the proportions of these three sesquiterpene lactones vary among forage chicory cultivars. To determine whether the individual compounds differ in anthelmintic activity, we prepared sesquiterpene lactone-enriched extracts from two cultivars, Grasslands Puna (Puna) and Forage Feast, and tested their effects on the hatching of eggs of Haemonchus contortus. The dominant constituents in the Puna and Forage Feast extracts were DOL and LAC, respectively; LPIC concentration was similar for the two cultivars. Extracts from both cultivars inhibited hatching of H. contortus eggs at all concentrations tested (P < 0.0001), but there were significant differences in egg responses to the two extracts (P < 0.0001). With Puna, egg hatching decreased sharply in a linear fashion when total sesquiterpene lactone concentrations (LAC + DOL + LPIC) were between 0 and 5.0 mg/mL. Approximately 90% inhibition was observed when the concentration was 5.0 mg/mL or higher. A biphasic effect on egg hatching occurred with the Forage Feast extract. The fraction of eggs that hatched decreased gradually to 65% as the sesquiterpene lactone concentration increased from 0 to 6.7 mg/mL. Treatment with higher concentrations resulted in a sharp decline in hatchability, and 88% inhibition was achieved when eggs were exposed to a concentration of 10 mg/mL. Probit dose-effect analysis for total sesquiterpene lactones in the extracts yielded LC50 values of 2.6 mg/mL for Puna and 6.4 mg/mL for Forage Feast. Results indicate that DOL is more effective than LAC against H. contortus eggs. Thus Puna may be a better choice than Forage Feast for bioactive pastures for H. contortus control in small ruminants.