Sheep trial 2 involved 36 castrate male lambs fed a combination of low and high protein diets with and without 50g/kg feed quebracho tannin. Both increased dietary protein concentration and tannin inclusion reduced nematode burden (as expressed as daily faecal egg output) but the effects were not additive. Indeed, in sheep fed the high protein diet with quebracho tannin, daily faecal egg output was similar to control animals fed the low protein diet without quebracho tannin.
Mechanisms of action of quebracho tannin.
Haematological parameters analysed from sheep trial 2 indicate dietary quebracho tannin does not appear to enhance the immune response of the parasitised host. Rat trials involving Nippostrongylus brasiliensis infection (lumen dwelling worm, similar to Trichostrongylus colubriformis ) and Trichinella spiralis infection (mucosal dwelling worm, not exposed to gut contents once established in the host) resulted with tannin-fed rats having reduced Nippostrongylus burdens but no reduction was seen in tannin-fed rats infected with Trichinella. A subsequent rat trial involving immune-suppressed rats infected with Nippostrongylus brasiliensis indicated that both immune-suppressed tannin-fed and non-suppressed tannin-fed rats had reduced worm burdens compared to control-fed rats (no tannin). The rat trials suggest that quebracho tannin could be acting directly against the worm by being toxic or through its action on the intestinal epithelium increasing mucus secretion and cell sloughing, which are associated with worm rejection. In vitro studies incubating adult Nippostrongylus brasiliensis in increasing concentrations of quebracho tannin demonstrated that adult worms incubated in control media survived for longer periods of time than those in quebracho tannin media. This data suggests that quebracho tannin is toxic to the worm causing accelerated worm death.
In conclusion dietary quebracho tannin reduces nematode infection of the host. Results indicate that a feasible potential mechanism of action of quebracho tannin seems to be direct toxicity against the worm. Increased endogenous secretions from the intestinal epithelium are also possibly involved. Any direct enhancement of the immune system promoting worm expulsion is unlikely. The studies above involved a commercially available chemically extracted condensed tannin and any beneficial results could be attributed to compounds resulting from the extraction. A small quantity of chemically-untreated quebracho tannin was available for use. A small rodent trial indicated that reduced worm burdens were also seen in rats fed chemically-untreated tannin and in vitro assays of worm motility suggest that adult worm survival rate is compromised by the presence of chemically-untreated tannin to a greater extent than chemically-treated tannin. It should be remembered that the results gained from these studies may only be applicable to quebracho tannin and/or the nematode and host investigated.
The results obtained indicate that natural dietary tannins may be a method of controlling intestinal parasites in domesticated ruminants found in target regions.
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