The nutritive value of Acacia saligna and Acacia salicina for goats and sheep

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Abstract
Acacia saligna and A. salicina phyllodes, harvested in autumn from young and mature trees, were fed as sole diets to goats (20·3 (s.d. 4·8) kg; no. = 16) and sheep (32·6 (s.d. 4·9) kg; no. = 16). Crude protein of phyllodes from mature trees was 111 g/kg dry matter (DM) and from young trees ranged between 121 and 132 g/kg DM. Condensed tannins and ash content were about twice as high in young trees as in old ones and gross energy was higher in old trees than in young ones. DM intakes by goats from both tree species were low: 24·8 and 13·7 g/kg M0·75 per day for mature and young trees, respectively. Corresponding intakes by sheep were 20·4 and 11·5 g/kg M0·75 per day. Metabolizable energy intakes were up to 125 and 99 kj/kg M0·75 per day for goats and sheep, respectively and were higher for phyllodes from mature trees than for young trees. Goats lost up to 219 glday and sheep up to 346 g/day and both species were in negative nitrogen balance. DM, organic matter and energy apparent digestibilities were low for all diets but were generally higher for goats than sheep. It is concluded that neither A. saligna nor A. salicina could be used as a sole food for small ruminants because of low intakes and negative nitrogen balances. This appears to be due to high tannin content.