POLYETHYLENE-GLYCOL IS MORE EFFECTIVE THAN SURFACTANTS TO ENHANCE DIGESTION AND PRODUCTION IN SHEEP FED MULGA (ACACIA-ANEURA) UNDER PEN ANDPADDOCK CONDITIONS

Chemicals that interfere with the formation of tannin-protein complexe s were evaluated as dietary additives for mulga-fed sheep in pens and under paddock conditions. Condensed tannins (CT) in mulga inhibit prot ein digestion, and the use of chemicals to precipitate CT or dissociat e CT-protein complexes may improve production from sheep consuming a m ulga diet. In a digestion study with mulga-fed sheep in pens, provisio n of polyethylene glycol (PEG) at a rate of 6 g/day significantly (P < 0.05) improved nitrogen (N), phosphorus (P), and sulfur (S) balance, and apparent N, P, dry matter (DM), and organic matter digestibility, and the rate of liveweight gain. Addition of the surfactants SDS or al kanate 3SL3 to the diet of mulga-fed sheep did not improve N balance o r digestion; however, apparent digestibility of P, and P and S balance , were significantly improved by SDS. Teric PE64, a compound structura lly similar to PEG, significantly improved S balance, but not DM intak e or N balance. For sheep consuming a predominantly mulga diet under p addock conditions, provision of PEG at a rate of 12 g/day significantl y improved clean wool growth and liveweight gain compared with unsuppl emented sheep, by 9% and 100%, respectively (0.809 v. 0.745 mg/cm(2).d ay, and 44 v. 22 g/day). The studies demonstrated that although surfac tants can affect mulga digestion, using PEG to precipitate CT is more effective to improve mulga digestion and animal production than the us e of surfactants. However, the wool and liveweight production response s achieved with PEG were not sufficient to justify its wide-scale use for mulga-fed sheep. Consequently, alternative methods should be sough t to reduce the negative effects of mulga CT on sheep production.