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PEG Supplementation Trials Show no Effect

Tuesday, March 20, 2012

Can Poly-Ethylene Glycol (PEG) supplementation improve the performance of cattle grazing mulga (Acacia aneura) during severe dry periods? Research by Meat and Livestock Australia suggests that PEG supplementation had no effect on performance.

Description/Abstract:

Beef producers of central Australia requested research into Poly-Ethylene Glycol (PEG) supplementation to determine if it could improve the performance of cattle grazing mulga (Acacia aneura) during severe dry periods.

Previous research has found that PEG binds with the condensed tannins (found in the leaves of some plants including mulga) allowing more protein to be digested by ruminants.

An eight week long pen trial was conducted with Droughtmaster heifers (n=10, average liveweight 289kg ±6kg) individually penned with half receiving PEG-4000 supplement (14g – 105g PEG/head/day for weeks 1-6 and 200g PEG/head/day in weeks 7 & 8) and the other half no supplement.

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 CP%) and 21% poor quality hay (8.4 ME MJ/kgDM, 4.9%CP). The study found no significant difference (P>0.05) in live weight gain between the PEG and control heifers (mean 0.188 vs 0.314 kg/day), nor in DM intake (mean 4.3 vs 4.8 kgDM/day) or in vivo dry matter digestibility (mean 48% vs 50%).

There was significantly less nitrogen excreted in the faeces of the PEG heifers (p<0.001) (1.04% PEG v 1.36% control faecal DM) and significantly more nitrogen absorbed (N absorbed gDM/N intake kgDM) by the PEG heifers (802.8 N absorbed gDM/N intake KgDM PEG vs. 762.8 N absorbed gDM/N intake KgDM Control).

It was concluded that in this trial PEG supplementation had not been shown to have any effect on beef cattle performance and therefore could not be recommended to Central Australian pastoralists as a viable strategy for cattle management in dry conditions. It is hypothesised that other nutrients are required in addition to PEG to produce a benefit.

Final report summary:

The pastoral industry in central Australia, as represented by the Alice Springs Pastoral Industry Advisory Committee (ASPIAC), 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 (Jones and Mangan 1977, Perez-Maldonado 1994 and Miller et al. 1997). These condensed tannins are found in mulga (Plumb et al. 1999 and Pritchard et al. 1988), commonly browsed by cattle in central Australia (Chippendale 1964).

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 (p<0.001) during the period of high PEG supplement (1.04% PEG v 1.36% control animals faecal DM). As such more nitrogen was significantly (P<0.001) absorbed (measured as N absorbed gDM/N intake KgDM) by the PEG heifers (802.8 N absorbed gDM/N intake KgDM PEG vs. 762.8 N absorbed gDM/N intake KgDM Control).

The cost of the PEG delivered to Alice Springs was $7.20/kg. At the higher recommended level of supplementation for PEG this resulted in a cost of $1.44/head/day. This is very expensive in comparison to other forms of supplementation, eg. urea lick blocks delivered to Alice Springs that cost $1.65/kg or approximately $0.24/head/day.

Given the high cost of PEG supplementation and the lack of response found in this study it is concluded that there is little potential for use of PEG supplementation of cattle grazing mulga in central Australia. It is hypothesised that other nutrients are required in addition to PEG to give a benefit.

This project has been useful for the central Australian pastoral industry by raising awareness and understanding of the potential for the use of PEG as a supplement for cattle grazing mulga. This report will provide information for not only beef producers in central Australia but those throughout the rangelands of Australia where mulga is dominant in the landscape, i.e. approximately 1.5 million km2 (Plumb et al. 1999).

March 2012

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