Digestibility of Duddingtonia flagrans chlamydospores in ruminants: in vitro and in vivo studies

BACKGROUND: The use of Duddingtonia flagrans as a tool for the biological control of gastrointestinal nematodes (GIN) is a promising alternative to anthelmintics. The chlamydospores of D. flagrans are orally dosed and their thick cell wall gives them the capacity to resist digestion and pass through the gastrointestinal tract (GIT). Chlamydospores reaching the faeces are able to germinate and trap nematode larvae. The efficacy of this control method is based on reducing the numbers of infective larvae leaving the faeces. Techniques have recently been developed for quantifying the numbers of chlamydospores in faeces. As the number of non-digested spores could be relevant in the design and optimization of dosing programmes for the control of GIN infective larvae, the aim of the present study was to estimate the loss of D. flagrans chlamydospores during their passage through the ruminant gastrointestinal tract using in vitro and in vivo techniques. RESULTS: After in vitro rumen digestion, chlamydospore recovery was not different from the quantity originally incubated (undigested spores) (P > 0.05). In vitro rumen+abomasum digestion caused nearly 36% loss of the chlamydospores originally incubated (P < 0.05). Germination of chlamydospores classified as viable was 24.3%. Chlamydospores classified as non-viable did not germinate. Rumen digestion resulted in more spore germination (R1 = 35.7% and R2 = 53.3%) compared to no digestion (time 0 h = 8.7%). Subsequent abomasal digestion reduced germination (R1+A = 25%) or stopped it (R2+A = 0%). In vivo apparent chlamydospore digestibility in sheep showed a loss of 89.7% of the chlamydospores (P < 0.05). CONCLUSIONS: The loss of chlamydospores was evident under in vitro and in vivo conditions. Negligible amounts of spores were lost during the in vitro rumen digestion. However, in vitro rumen+abomasum digestion resulted in a chlamydospore loss of approximately 36%. In vivo passage through the sheep GIT resulted in a total loss of 89.7% of the orally administered spores.