USING dolomite fertiliser on perennial pastures or supplementing cattle with magnesium rich pellets could be a potential fix for dark cutting beef in pasture-fed cattle.
At the inaugural SA Cattle Producer Forum at Hahndorf, WA-based researcher David Pethick presented the latest results from Murdoch University and the University of Adelaide, which showed the costly problem may be impacted by the mineral content of pastures.
Access to good quality pastures has long been advocated as key to increasing glycogen levels pre-slaughter and minimising dark cutting. The recommendation is for cattle to grow at 0.8 to 1 kilogram a day.
But two extensive Meat & Livestock Australia-funded trials on King Island, Tas, and in South East SA conducted last year have both shown a highly-significant relationship between dark cutting incidence and the pasture magnesium levels.
As the magnesium levels increase the incidence reduces, even where there is no clinical deficiency.
Professor Pethick said there was considerable research showing the importance of magnesium for nerve and muscle cell function and reducing the stress hormone response across a range of livestock species.
But the results of more than 2000 head on King Island processed at a JBS abattoir and 5800 cattle in the SE processed at Teys’ Naracoorte abattoir had been “extraordinary”.
“This is two different parts of southern Australia involving different cattle, different feed types, different researchers and different abattoirs giving the same answer, so this magnesium story must have something in it,” he said.
The SA results showed as pasture magnesium increased from 0.2 per cent to 0.3pc, which are both in the normal range for magnesium, dark cutting reduced by more than 6pc. This indicates finisher cattle are experiencing low magnesium or sub-clinical grass tetany.
Low magnesium is caused by either inadequate ingestion of magnesium or additional dietary factors which block magnesium absorption in the rumen.
Lush, short, grass dominant pastures are typically high in potassium and crude protein but low in dry matter and effective fibre which disrupt magnesium absorption in the rumen.
Prof Pethick said addressing magnesium levels was a “tough fix”, with palatability and delivery an issue.
“Dolomite fertiliser is probably your simplest answer, but whether it will work across a long time, we don't know and you probably need to be near a dolomite source for it to be economical,” he said. “Magnesium boluses are expensive at about $20 each and don’t pay out enough magnesium per day.
“So the other way is magnesium oxide or causmag, which is quite cheap in a pellet or in a mineral lick for long-term application.”
Murdoch University is conducting a short-term supplementation trial feeding cattle half a kilogram of a magnesium rich, canola meal pellet for 10 days prior to slaughter. Sixty cattle have been fed the pellet containing 46 grams of magnesium sulphate and 9.5g of magnesium oxide per 500g.
