Senegalia brevispica leaves, flowers and young pods are browsed to a considerable extent by goats and sheep, but seldom eaten by cattle because of the thorny branches (Skerman, 1982). The leaves are among the preferred leaves by camels in Ethiopia (Bekele et al., 2013).
Digestibility and nutritive value
Leaves
Numerous browse species reported to be part of Ethiopian and Kenyan rangeland, among which Acacia abyssinica, Senegalia brevispica, Acacia mellifera, Acacia nilotica, Senegalia senegal, Acacia seyal, Acacia tortilis, Balanites aegyptiaca, Grewia bicolor, Grewia tembensis, Rhus natalensis, Vernonia cinerascens, Ziziphus mucronata, Albizia coriaria, Albizia amara and Maerua angolensis were assessed for their chemical composition and in vitro DM digestibility (IVDMD). During both dry and rainy seasons, Senegalia brevispica was found to rank high for protein content, and to have lower NDF and lower total condensed tannins than others browse species. However, Senegalia brevispica IVDMD was among the lowest (Abebe et al., 2012; Ondiek et al., 2010). Senegalia brevispica also belonged to the group of higher potential degradability within 48h (Ondiek et al., 2010). The same experiment reported that in vitro OM digestibility was only medium (Ondiek et al., 2010). This result is in accordance with a former conclusion on the medium nutritive value of Senegalia brevispica among other acacia species in the Rift Valley of Kenya (Abdulrazak et al., 2000a). The authors of those experiments all concluded that the assessed browse species had potential value for ruminant feeding. In addition, it was reported that the use of Japanese yeast could enhance ruminal fermentation of those browses (Wambui et al., 2012; Wambui et al., 2010).
Pods
The in vitro OMD of Senegalia brevispica pods after 48h was 559 g/kg DM.
Sheep and goats
In Kenya, foliage of Senegalia brevispica was offered as a protein supplement to goats fed on a Rhodes grass hay-based diet, during the dry season. It had high protein content, low tannins and provided the highest amount of lipids among other foliages of legume trees assessed in the experiment. The relative high protein content of the browse (15-25% DM) advocated for the use of the browse leaves to supplement crop residues such as straw and/or low-quality pastures. The NDF content of the browse species was low to moderate, indicating a potential high digestibility. Browse fibre was shown to be more digestible than crop residue and mature grass hence could be easily utilized by animals (Kemboi et al., 2017a; Kemboi et al., 2017b).
In Ethiopia, sheep and goat wethers fed during 18 days ad libitum tef straw and vetch (Vicia dasycarpa) supplementation, or Senegalia brevispica leaves or sesban (Sesbania sesban) leaves in order to replace 33% or 67% of vetch, had lower N retention on acacia foliage than on sesban foliage. Tannins of Senegalia brevispica may have decreased protein digestibility by the formation of indigestible tannin-protein complexes (Woodward et al., 1997). In an earlier experiment, the level of tannins or lignin brought by Senegalia brevispica had been suspected to be the cause of a low palatability of the diet. This decrease in palatability was higher in sheep than in goat wethers (Woodward et al., 1995).
Senegalia brevispica leaves were fed as a protein supplement to sheep in the Borana region of Kenya. Three other protein supplements were assessed: babul (Acacia tortilis) pods, cowpea (Vigna unguiculata) hay and alfalfa (Medicago sativa) hay. The supplementation with acacia leaves resulted in lower DM intake than with other forage legume products, and it also resulted in lower DM and OM digestibilities than other products. Supplementation with forage legume products always resulted in lower grass intake but it increased N intake by 71% on average, compared to the control, and acacia diets were higher than cowpea and alfalfa diets. Growth rates and diet conversion efficiency for supplemented sheep were increased (P<0.01), compared to the controls by an average of 74 and 54%, respectively (Coppock et al., 1992).
In Kenya, the overall diet of goats fed Senegalia brevispica pods had higher protein digestibility and ammonia concentration. Goats had higher feed intake, but did not grow as fast as goats fed on other browse species pods such as those of umbrella thorn (Acacia tortilis) or babul (Acacia nilotica) (Sawe et al., 1998).
Calves
In Ethiopia, leaves of Senegalia brevispica, babul (Acacia tortilis) pods, cowpea (Vigna unguiculata) hay and alfalfa (Medicago sativa) hay were included in calf diets in the range of 300-380 g DM/d (as fed basis). These forage legumes were assessed for their use as protein supplements in the diet of calves receiving a native grass hay based diet (mixture of Hyparrhenia, Andropogon and Pennisetum spp.). Calves supplemented with forage legumes were allowed to graze dry season forage. The higher feed intake was for alfalfa hay and babul pods (86%), lower (71%) for Senegalia brevispica leaves and cowpea hay. N intake was the lowest for Senegalia brevispica leaves (8.1 g/d) and calf growth rate on acacia leaves could not compare with that on alfalfa. All supplemented diets increased N intake, growth rate, and liveweight gain of calves compared with the control. Supplementation decreased the overall DM intake of the calves. The use of Senegalia brevispica leaves, in spite of their low DM yield and the difficulties in harvesting them by hand due to their prickly stem, was encouraged since it could help controlling this species in the higher elevations of the Borana region of Ethiopia (Coppock et al., 1992).
