Abstract: Condensed tannins (CT) extracted from sulla (Hedysarum coronarium) were incubated with total soluble leaf protein extracted from white clover (Trifolium repens) and rumen fluid in order to determine the effects on the degradation of the large subunit (LSU) and small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). In the absence of CT, incubation with rumen fluid resulted in a rapid degradation of the LSU and SSU, although degradation of the LSU tended to be faster than that of the SSU and the degradation rate was significantly (P<0.001) higher than that in the incubations without rumen fluid. Addition of 150, 300 and 600 ?g per ml of CT from sulla to the incubations decreased (P<0.05-0.001) the rate of degradation of both LSU and SSU of Rubisco. At all concentrations of CT, addition of polyethylene glycol (PEG) eliminated the inhibition attributable to CT. The effect of CT extracted from sulla on the viability of the infective third-stage (L3) larvae of three gastrointestinal nematodes (Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus colubriformis) was tested by a larval migration inhibition (LMI) assay in vitro. The LMI assay measures the ability of the test material to immobilise the larvae and inhibit their passage through 20 ?m nylon mesh sieves. Extracts of CT from sulla were added to rumen and abomasal fluids (collected from sheep fed lucerne chaff) to provide concentrations similar to these observed in the abomasal digesta of sheep when CT-containing forages were fed (50-1000 ?g/ml). Incubation of L3 larvae in these fluids containing sulla CT reduced the viability, relative to the larvae in the control incubations (no CT added). This study showed that the larvae of T. colubriformis were more resistant (P < 0.001) to the inhibitory effect of CT from sulla than were the larvae of the other nematodes. When the larvae of these nematodes were incubated in rumen fluid containing 1000 ?g CT/ml, fewer larvae of T. colubriformis (37%) failed (P < 0.001) to pass through the sieves than those of O. circumcincta (59%) and H. contortus (72%). Addition of 2 ?g PEG/ ?g CT to the incubations eliminated the inhibitory effect of CT on larval viability through inactivation of CT, particularly in the rumen fluid.
Abdul L. Molan, Rebecca Alexander , Ian M. Bbookes and Warren C. McNabb , 2004. Effects of Sulla Condensed Tannins on the Degradation of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (Rubisco) And On The Viability of Three Sheep Gastrointestinal Nematodes In vitro. Journal of Animal and Veterinary Advances, 3: 165-174.