The effect an extract of sulla (Hedysarum coronarium) containing condensed tannins (CT) had on the viability of the infective third-stage larvae (L3) of three gastrointestinal nematodes (Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus colubriformis) was tested by the larval migration inhibition (LMI) assay in vitro. The LMI assay measures the ability of test material to immobilize larvae and prevent their migration through 20 mm nylon mesh sieves. The extract from sulla was added to rumen (RF) and abomasal fluid (AF), collected from sheep fed lucerne (Medicago sativa) chaff, to provide concentrations of CT similar to those observed in the rumen and abomasal digesta of sheep fed CT-containing forages (50-1000 mg/ml). Incubation of L3 larvae in rumen and abomasal fluid containing the sulla extract reduced the migration of larvae compared to those in control incubations (no extract added). This study showed that the larvae of T. colubriformis were more resistant (PO. circumcincta (RF 59%; AF 79%) and H. contortus (RF 72%; AF 81%) were significantly (PT. colubriformis (RF 37%; AF 26%). Addition of 2 mg polyethylene glycol (PEG)/mg CT to the incubations partially reduced the effects of the sulla extract on larval migration, particularly in the rumen fluid, suggesting that CT was responsible for most but not all of the inhibitory effect of this extract.

AL, Molan, R Alexander, IM Brookes, and WC McNabb

Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 21-25, 2000
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