Studies on Sapindus rarak DC as a defaunating agent and its effects on rumen fermentation
The aim of the work described here was to examine the antiprotozoal activity of the pericarp from Sapindus rarak DC (Sapindaceae) for its potential to defaunate the rumen, either partially or completely, without having a detrimental effect on the bacterial population and on rumen fermentation, and hence enhancing rumen productivity. An approach to improving microbial efficiency in the rumen is to eliminate protozoa (defaunation). Elimination of protozoa by chemical means is potentially the most convenient method. However, it is likely that some chemicals are not toxic specifically to the protozoa and probably kill other microorganisms and host cells in the rumen, therefore novel natural antiprotozoal agents are being sought. A possible role for saponins has been of interest to many researchers as saponins induce marked reductions in rumen protozoa numbers, particularly when the animal is fed on high-concentrate diets. The susceptibility of rumen protozoa and lack of susceptibility of rumen bacteria to saponins is explained by the reaction of saponins with membrane sterols, which are present only in eukaryotic membranes and not in prokaryotic bacterial cells. Recent in vitro results suggest that S. rarak exhibited higher immobilising activity and produce higher activity to lyse the cells compared to other saponin-containing plants. A preliminary study on the antiprotozoal activity of the active agent present in the pericarp of fruits of S. rarak, well known for the high saponin content of its fruits, was carried out. An antiprotozoal assay was developed. The results were consistent within experiments, but not between experiments, possibly due to the number of protozoa fluctuating widely with time. A study on the effect of Sapindus rarak on rumen bacteria, using a quantitative plating method, showed that there was no effect on rumen bacteria. Raw material and extract of pericarp of S. rarak were screened for their effects on rumen protozoa and bacteria (with a view to predicting its safety as a feed supplement and for its potential to defaunate the rumen, either partially or completely). The pericarp of S. rarak was extracted using selective extraction of saponins with CIS support. The fractions were collected and monitored by Thin Layer Chromatography (TLC). The active compounds were tested in vitro for toxicity to rumen protozoa by visual assessment of protozoal viability (Nottingham studies) and by measuring the degradation of labelled bacterial protein by rumen protozoa (Aberdeen studies). The influence of methanol extract of S. rarak on growth of pure cultures of rumen bacteria was also examined (Aberdeen studies). The results showed that the saponin fractions of S. rarak exhibit antiprotozoal activity as confirmed by visual assessment as well as by measurement of the breakdown of 14C-Ieucine-Iabelled Prevotella bryantti in rumen fluid incubated in vitro. No evidence was found of protozoal resistance to S. rarak. Inclusion of methanol extract of S. rarak in the growth medium of pure cultures of rumen bacteria had no effect, except that cellulolytic bacteria showed susceptibility. Extracts appeared in this study to prolong the lag phase following inoculation of Streptococcus bovis or inhibit the growth of Butyrifibrio fibrisolvens, Ruminococcos albus, and Ruminococcos flavefaciens. It seems that antibacterial properties were more pronounced against gram-positive bacteria, similar to the action ofionophores (McGuffey et al., 2001). A study on the effects of S. rarak on ruminal digestion, fermentation and ammonia concentration, using ruminally and duodenally cannulated dairy cows, showed that direct administration of S. rarak into the rumen did not decrease protozoal numbers in vivo. However, there were some indicators of selective activity against holotrichs. Changes in propionate concentration in the rumen and lack of change in microbial flow parameters suggest no adverse effects on other fermentation measures. Increased production of propionate is beneficial to the animal by affecting the capture of fermentation energy in the rumen. S. rarak caused a decrease in ammonia concentration. The observed ammonia levels represent a balance between the processes of degradation of feed protein and uptake of ammonia for synthesis of microbial protein. The lower ammonia levels could be due to higher incorporation of ammonia, peptide, or amino acids into microbial protein. In conclusion, S. rarak tested in this study has a great potential for suppressing rumen ciliate populations, but exerted negligible general effects on ruminal fermentation. Therefore, controlling rumen ciliate protozoa would be expected to lessen the dependence on protein supplementation under high-production conditions and would also be beneficial under conditions where the quantity of protein absorbed from the post-ruminal gut limits animal productivity, which occurs frequently in animals receiving low-quality tropical forages.