The potential of controlling gastrointestinal parasitic infections in tropical small ruminants using plants high in tannins or extracts from them

A series of previous studies with quebracho tannin (QT) had shown that the tannin was effective at reducing the worm burden of temperate sheep infected with Haemonchus and Trichostrongylus. The potential of using tanniniferous browse plants available in the tropics as a means to reduce or control nematode infections of small ruminants was, therefore, investigated. Leaves of different browse trees and shrubs were assayed for condensed tannin (CT) concentration using a colorimetric method. Five species with the highest levels were sampled monthly and analysed in order to map their seasonal variation in CT. The level of CT in the leaves ranged between 58 – 283g kg DM. Purified quebracho tannin was used as the standard. Seasonal changes in CT levels were affected by the stage of leaf maturity with peak levels occurring after the end of main rain season in June. Anthelmintic activity of crude extracts from leaves of two of the plants shown to have a high tannin content (Acacia polyacantha and Tamarindus indica) and that of commercial tannin preparation from wattle tree (WT) was then tested in vitro against freshly isolated goat nematodes. Time of death of the parasites was recorded. Survival of the nematodes was significantly (P<0.001) reduced by both leaf extracts and by the WT. Acacia sp. leaves were then feed to goats to investigate their effect on faecal egg output and worm burdens of animals with a mixed nematode infection. Twenty-four bucks were infected with a single dose of nematode larvae and faecal egg counts (FEC) were monitored regularly. On day 38 post-infection (p.i.), half of the goats were offered a supplement of dried acacia leaves at 130g per animal for 20 days while the remaining half (control) received a grass supplement with comparable nutritional value but without condensed tannins. All goats were humanely slaughtered at the end of the trial for worm burden estimation. Mean FEC of the acacia-fed group was 27 per cent lower with a slight reduction (13 per cent) in the population of the large intestine worm, Oesophagostomum columbianum, compared to the control group. In a second trial, 36 bucks were infected as before and then randomized on the basis of their FEC into three equal groups 30 days after infection. For three consecutive days one group received 1.2g WT/kg body weight, one 2.4g WT/kg and the third group received a placebo drench. All goats were humanely slaughtered on day 42 p.i. Neither FEC nor worm burdens were significantly reduced by the drench administration. This is in contrast to studies with quebracho tannin and temperate sheep conducted earlier. Studies are also required using sheep reared in the tropics to determine whether the apparent species differences are real rather than due to adaptation of the animals to tannins prior to the experimental study. It is not possible yet to come to a definitive conclusion on the value of tannins in controlling parasitic infections in tropical small ruminants. The potential of controlling gastrointestinal parasitic infections in tropical small ruminants using plants high in tannins or extracts from them