Nutritive value of Acacia tree foliages growing in the Limpopo Province of South Africa

Abstract

Acacia trees form the third largest woody plant family in southern Africa and are an important ecological component of the bushveld vegetation that is prevalent in the Limpopo Province of South Africa. The purpose of the study was to determine types and amounts of tannins and also to evaluate the nutritive value of tree foliages, Acacia karroo, Acacia nilotica, Acacia tortilis, Acacia galpinii, Acacia sieberiana, Acacia hebeclada and Acacia rhemniana, grown in the Limpopo Province and also to determine types and amounts of tannins occurring in them. Young leaves with petioles from seven tree foliages were collected from five different trees per species at the University of the North (now University of Limpopo) in April 2003, in a completely randomized design. Packed volume ranged from 1.50 mL/g for A. karroo to 3.00 mL/g for A. hebeclada whilst water retention ranged from 3.71 g/g for A. galpinii to 4.98 g/g for A. sieberiana. These results suggest that all the tree leaves have a high intake potential. All the Acacia species had crude protein levels above 100 g/kg dry matter (DM), ranging from 103 g/kg DM for A. rhemniana to 183 g/kg DM for A. sieberiana. Crude protein levels of this magnitude in a diet are adequate to support the maintenance requirements of cattle, sheep and goats at low to medium production levels. The Acacias contained medium to high levels of neutral and acid detergent fibres with ranges of 488 to 622 and 415 to 545 g/kg DM, respectively. In vitro DM and organic matter degradabilities varied from 345 to 534 and 254 to 474 g/kg DM, respectively. Acacia hebeclada, A. sieberiana and A. galpinii contained traces of total phenolics whilst A. tortilis contained approximately 90 g/kg DM of total phenolics and A. karroo, A. nilotica and A. rhemniana contained intermediate concentrations. Extract condensed tannin (CT) content ranged from 1.1 g/kg in A. hebeclada to 80.7 g/kg in A. karroo. At level above 50 g/kg, CT tends to negatively affect intake and digestibility in ruminants. Consequently, reduced intakes of A. galpinii, A. karroo and A. tortilis could be expected because they contained CT values above 50 g/kg. Only A. nilotica showed a sharp curve in the potassium iodate test, reflecting its considerable content of hydrolysable tannins (HT). All the other species had flat curves reflecting low levels of HT in them. The results showed that all the species except for A. galpinii, A. karroo and A. tortilis are of good nutritive value and have a potential for integration into livestock feeding systems in the Limpopo Province.

South African Journal of Animal Science Vol. 35(4) 2005: 221-228