The effect of wattle tannin drench or an acacia meal supplement on faecal egg counts and total worm burdens of tropical sheep with an experimental nematode infection

Following on from our studies on the potential use of tannins to control intestinal parasites in small ruminants we recently conducted two further trials to investigate the effect of a wattle tannin oral drench (WT), or supplementation of the diet with acacia (AMS), on faecal egg counts (FEC) and worm burdens of growing tropical Black Head Persian (BHP) sheep with an experimental intestinal nematode infection. In trial 1, 28 rams infected with a single dose of 1,500 mixed nematode larvae per 20 kg body weight were used. Faecal egg counts (FEC) were monitored regularly throughout the study. On day 30 post-infection, the infected sheep were blocked on the basis of their egg numbers and randomly assigned into two equal groups. For three consecutive days one group received a tannin drench at 1.5 g WT/kg body weight, and the remaining group received a placebo. All sheep were humanely slaughtered on day 42 post-infection and their worm burdens were assessed. Worm burdens and FEC were reduced (P<0.001) by the drench administration. Faecal mucus and water contents were increased. Trial 2 used another 28 infected growing BHP rams and had an identical design to trial 1, except that from day 30 post-infection animals in one group of 14 rams were offered 150–170 g of AMS daily, whereas in the other group they were offered Pannicum meal as control. On day 60 all animals were slaughtered for worm burden estimation. There was only a slight reduction in FEC (19 per cent) but none in the worm burdens. The first trial demonstrated that the WT drench had significant activity against important nematodes of tropical sheep, as opposed to its small effects in infected tropical goats reported previously, suggesting that there are species differences between the two hosts. Feeding the acacia meal (trial 2), which is high in tannins, appeared to have little effect.