Establishment and fecundity of Ostertagia circumcincta and Trichostrongylus colubriformis in lambs fed lotus (Lotus pedunculatus) or perennial ryegrass.

Forty four 12-14 week old Polled Dorset ram lambs, raised helminth free from birth, were used to investigate the effects of condensed tannins (CT) in lotus (Lotus pedunculatus) on lamb growth and gastrointestinal nematode establishment and fecundity. Condensed tannins bind to proteins in the rumen and increase the flow of protein to the intestines. Lambs were allocated to either a ryegrass (Lolium perenne) or lotus diet fed ad libitum, with or without twice daily drenching of polyethylene glycol (PEG) which binds with and deactivates the CT. One week after allocation to the diets, each lamb was infected per os with 10,000 Ostertagia circumcincta and 10,000 Trichostrongylus colubriformis larvae and slaughtered 28 or 29 days later. Lambs fed lotus had lower faecal egg counts (P < 0.0001) and lower O. circumcincta burdens (P < 0.001), fewer female O. circumcincta (P < 0.0001) and higher faecal dry matter (P < 0.001) than lambs fed ryegrass, but numbers of T. colubriformis nematodes were not affected. This trial did not ascribe beneficial effects of L. pedunculatus to CT per se and the use of PEG does not seem appropriate to studies of parasitology.