Acacia saligna as a supplementary feed for grazing desert sheep and goats

Acacia saligna, a leguminous tree, has a high crude protein content, remains green all year and can be grown in deserts using only runoff water. However, dry matter intake (DMI) by sheep and goats of A. saligna is low, presumably due to its high tannin content. It has been suggested that DMI could be increased by such methods as wilting of the forage and by neutralizing the negative effects of tannins by tannin-complexing agents. The purpose of this study was to determine DMI of supplementary A. saligna (phyllodes and small stems) by grazing sheep (∼ 50 kg) and goats (∼ 37 kg) when the animals were (1) offered wilted or fresh material (Expt 1); and (2) administered with polyethylene glycol (PEG), a tannin-binding agent (Expt 2). In this second experiment, there were three 14-day periods in which one group each of sheep and goats was on a regime of: No PEG–PEG–No PEG, whereas another group was on a regime of: No PEG–No PEG–PEG. In Expt 1, the DMI of A. saligna was statistically higher in goats than in sheep, but there was no difference in intake between fresh and wilted material. Average DMI of A. saligna, both fresh and wilted, was 124·1 g/day or 8·41 g/kg0·75 per day for goats and 94·1 g/day or 5·05 g/kg0·75 per day for sheep. Goats and sheep consuming fresh A. saligna gained more body mass than their respective controls; the difference was significantly greater in goats but not in sheep. In Expt 2, DMI of fresh A. saligna in the first period (before PEG) was 104·1 g/day or 7·16 g/kg0·75 per day for goats and 84·8 g/day or 4·51 g/kg0·75 per day for sheep. Administration of PEG during the second period resulted in an increase in DMI of 62% in goats and 83% in sheep. These animals maintained a high A. saligna intake in the third period when PEG was withdrawn. Goats and sheep that did not receive PEG in the second period had similar A. saligna intake as in the first period, but increased intake by 62% and 47%, respectively, with PEG in the third period. Overall, the two goat groups and two sheep groups consuming A. saligna lost less body mass than their respective controls; the difference was significantly less in sheep but not in goats. It was concluded that wilting A. saligna did not increase DMI. Administration of PEG increased A. saligna intake and the intake remained high after PEG was withdrawn. Offering A. saligna as a supplement had a positive effect on body mass change.