Determining the effectiveness of Poly Ethylene Glycol (PEG) in the utilisation of topfeed by cattle in central Australia.

Summary

The pastoral industry in central Australia, as represented by the Alice Springs Pastoral Industry Advisory Committee, requested that further research be conducted into the use of Poly-Ethylene Glycol (PEG) as a supplement to cattle grazing or browsing mulga (Acacia aneura). Previous research has found that PEG binds with the condensed tannins, found in mulga and similar plants, allowing more protein to be digested by ruminants. These condensed tannins are found in mulga, commonly browsed by cattle in central Australia.
The objectives of this project were to determine the cost effectiveness of PEG supplementation at various levels and if there was a positive response from the pen feeding trial, provide economic and grazing recommendations for supplementing breeder cattle. The first objective was achieved as a result of the pen trial. The second objective was not completed due to there being no improvement in the heifer performance from the PEG supplementation and seasonal conditions were not conducive to a paddock trial being conducted. An eight week pen trial was designed with ten Droughtmaster heifers individually penned; half supplemented with PEG-4000 and half as a control without PEG. During the first six weeks the PEG heifers were supplemented with PEG in their drinking water at a variable low rate (due to variation in water intake) with a median amount of 60g/head/day (range 14 - 105 g/head/day). During the final two weeks the PEG heifers were drenched daily at a higher level of PEG supplementation (200g/head/day).
To replicate the diet of cattle during severe dry periods, the diet was comprised of on average 79% mulga (7.6 ME MJ/kgDM, 18.2% Crude Protein(CP)) and 21% poor quality hay (8.4 ME MJ/kgDM, 4.9%CP). Animals were weighed weekly for eight weeks and during the final two weeks daily dry matter intake and weekly dry matter digestibility and nitrogen excretion were recorded. There was no difference (P>0.05) in liveweight gain between the PEG and control heifers for the entirety of the pen trial (mean 0.188 vs 0.314 kg/day), in Dry Matter (DM) intake (mean 4.7 vs 4.2 kg/day) and DM digestibility (mean 50% vs 48%). There was significantly less nitrogen excreted in the faeces of the PEG heifers.