ACACIA SALIGNA AS A FODDER TREE FOR DESERT LIVESTOCK AND THE INTERACTION OF ITS TANNINS WITH FIBER FRACTIONS

Acacia saligna was examined as potential fodder for sheep (27.4 kg) an d goats (14.8 kg) raised in arid and semi-arid areas. This leguminous tree remains green all year and can be grown in deserts using only run off water. Phyllodes collected in March had a crude protein content of 12.5% dry matter (DM) and high tannin content (tannins as tannic acid equivalent to 11.3% and condensed tannins as leucocyanidin equivalent to 8.3% DM). DM intake was low, amounting to 0.80% and 1.05% body mas s daily for sheep and goats, respectively. Sheep lost 227 g day(-1) an d goats 196 g day(-1) while on this diet. Dry matter, organic matter a nd energy digestibilities were low in both species but were higher for goats than for sheep, and negative digestibilities were measured for acid detergent fibre (ADF) and acid detergent lignin (ADL). Metabolisa ble energy intake for goats was 121.9 kJ kg(-0.75) day(-1) and for she ep was 78.6 kJ kg(-0.75) day(-1). Apparent N digestibility was 17.5% a nd 0.9% for goats and sheep, respectively, and both species were in ne gative N balance of 0.25-0.30 g kg(-0.75) day(-1). Total water intake and output were higher in sheep than in goats. Extractable tannins wer e virtually absent in faeces in both species, however, output of conde nsed tannins and protein in the ADF and ADL fractions were substantial ly higher. This showed the presence of tannin-protein complexes in the se fractions which explained the negative digestibilities of ADF and A DL. It was concluded that Acacia saligna could not be used as a sole d ietary source for small ruminants because of low intake and negative n itrogen balance. This was due mainly to the high tannin content. Howev er, the tree might have a potential as a supplementary fodder due to i ts high crude protein content.