Heather (Calluna vulgaris) supplementation does not reduce trapping ability of Duddingtonia flagrans in faeces of Haemonchus contortus infected lambs

Infection with gastro-intestinal nematodes (GIN) seriously impairs productivity and health of grazing animals. Due to the considerable rise in anthelmintic resistance and the increasing popularity of organic farming, alternative control strategies will replace or complement traditional anthelmintics. The efficacy of two potential alternatives (i) feeding the tanniferous forage heather (Cantina vulgaris) and (ii) the nematophagous fungus Duddingtonia flagrans (isolate FiBL-DF-P14), was tested in a feeding experiment with lambs artificially infected with Haemonchus contortus. Animals received hay supplemented with heather or with a late cut hay (ecohay) as a control feed ad libitum for three weeks. Two doses (1 x 10(5) and 5 x 10(4) chlsp/kg LW) of D. flagrans chlamydospores (chlsp) were administered to animals of each roughage treatment and H. contortus larval recovery from faecal cultures was compared with an untreated control (6 animals per D. flagrans-heather combination). Protein, crude fiber and energy contents of ecohay and heather were similar but heather contained approximately twice more fat, four times more lignin and ten times more of all condensed tannin fractions. Heather contained 17.3 mg Proanthocyanidin per g dry matter (DM) while contents of ecohay were 1.7 mg/g DM. Daily average feed intake across both treatments was 1.5 kg DM/animal/day, of which heather/ecohay intake accounted for 0.17/0.19 kg. Overall, there was no significant effect of heather on faecal egg counts (FEC). There was a tendency for a significant interaction between feed supplement and time and a significantly (p = 0.030) lower FEC of nominally 1799 EPG in the heather treatment at the end of the heather feeding period compared with the ecohay treatment. Lambs in this study consumed less heather than grazing sheep in other studies, even though condensed tannin contents were comparably low. Heather supplementation did not affect larval recovery in faecal cultures and trapping ability of D. flagrans. As compared with the untreated control, both doses of D. flagrans reduced larval recovery by 96.2 % and 95.5 %, respectively (p < 0.001), with no significant difference between the doses. The isolate FiBL-DF-P14 was at least as effective as isolates tested in other studies and achieved over 95 % reduction at a low dosage of 5 x 10(4) chlsp/kg LW. In conclusion, our results confirm the potential of and indicate no negative interactions between both alternative GIN control methods.