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Supplementation to reduce the impact of mycotoxins and insufficient magnesium

Project start date: 21 March 2017
Project end date: 31 August 2020
Publication date: 18 September 2020
Livestock species: Grassfed cattle
Relevant regions: Victoria, South Australia, Northern Territory, Tasmania
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In southern Australian grassfed beef systems, dark cutting is a major cause of carcase non-compliance (within MSA), caused by low muscle glycogen levels at slaughter. These muscle glycogen levels have been shown to be negatively effected by a lack of magnesium absorption, and also by ingestion of mycotoxins produced by endophytes in pastures. 

This project studied the impacts of varying potassium (K) and crude protein levels (both of which impact magnesium absorption) on muscle glycogen, as well as the effect of magnesium and mycotoxin binder supplementation (in separate experiments) on the prevalence of dark cutting. 

While there were no significant impacts of K or crude protein on magnesium absorption observed, magnesium supplementation was recommended in circumstances where pasture magnesium (Mg) levels are low, rumen flow rates are high, or total dry matter intake levels are insufficient.  Supplementation with a mycotoxin binder did not have a significant effect in this experiment.


The main aims of this project were to determine:

  • impact of varying protein on glycogen
  • impact of varying K on glycogen
  • impact of Mg supplementation on dark cutting incidence
  • impact of mycotoxin binder supplementation on dark cutting incidence
  • the best way to develop young scientists.

Key findings

  • Varying levels of K and crude protein did not appear to impact muscle glycogen stores in the grassfed cattle.
  • Mg supplementation was only effective in increasing muscle glycogen when Mg absorption was limiting.
  • Mycotoxin binder supplementation did not appear to affect dark cutting incidence, but mycotoxin presence was not detected.

Benefits to industry

The results of this project highlights the importance of maximising pasture intake (grazed at 3 leaf stage where possible) or replacing pasture with hay to provide the best change of ensuring adequate magnesium intake through the growing season (not just for dark cutting but also for a whole range of other benefits that Mg provides). 

Pasture tissue testing might highlight mineral deficiencies that could be overcome with adequate supplementation with commercially available sources.  If grazing old pastures that contain endophytes, there might be times of year when feeding a mycotoxin binder would be beneficial in reducing the rates of dark cutting.

MLA action

The outcomes are being used to prepare Tips n Tools for distribution and promotion through print and electronic media. Edge and Profitable Grazing Systems (PGS) programs will be reviewed to include some of the key findings.

More information

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Primary researcher: University of New England