The evaluation of Acacia and other tree pods for goats: influence of rumen fluid source and polyethylene glycol addition on in vitro gas production

After prolonged exposure to tanniniferous diets, it has been reported that some rumen microorganisms acquire defensive mechanisms against tannins (Brooker et al., 2000) or produce tannin-degrading enzymes. Such rumen microorganisms are said to be “tannin resistant” as their fermentation activity is less inhibited by the presence of tannins in the host’s diet. As acacia pods contain tannins their use as protein supplements for goats in the dry season may require that they be first detannified e.g. by using polyethylene glycol (PEG). However, goats with prior exposure to tanniniferous diets may have developed adaptive mechanisms to deal with tannins. This study, therefore, investigated the need for tannin inactivation in feeds given to ‘adapted’ animals by comparing the effect on the in vitro fermentation of tree pods incubated with and without PEG using rumen fluid from adapted and unadapted goats.

The fate of mature African Acacia pods and seeds during their passage from the tree to the soil

ABSTRACTThe fate of mature Acacia tortilis pods on the tree and ground and A. nilotica pods on the ground were investigated at a site in South Africa. Pods on Acacia trees were browsed only by giraffe whereas pods on the ground were browsed by kudu, impala, steenbok and duiker. In the absence of giraffe most A. tortilis pods fell from the tree to the ground. When giraffe were present they consumed most A. tortilis pods at tree level. Bruchids infested 21.6–54.0% of seeds within pods on the tree. Once fallen, in the absence of browsing ungulates, A. tortilis and A. nilotica pod and seed disappearance could be attributed to burial by termites and ants, seed consumption by rodents and to decomposition; when browsing ungulates were present they consumed most pods on the ground. Between 20.0–47.6% of A. tortilis and 31.0–58.0% of A. nilotica seeds on the ground were infested by bruchids. Ungulate browsing had no effect on bruchid infestation of seeds. This study exemplifies the importance of browsing ungulates as consumers of Acacia pods. Although survival of A. tortilis and A. nilotica seeds was greatest in the absence of browsing ungulates the survival of seeds following pod consumption by ungulates is unknown.