Dark-coloured beef attracts a penalty for producers and retailers alike, and is not favoured by consumers, so Kate Loudon has investigated solutions to reduce its affect.
As part of her research at Murdoch University, Dr Loudon found that high pH values produce darker cut meat.
“The higher pH dark meat is rejected by consumers because it doesn’t eat well, but also the high pH makes the meat more prone to bacterial overgrowth so it has a reduced shelf life,” she said.
Dark cutting costs producers $150 a carcass, which equates to a penalty of about $17 million a year.
Dr Loudon said dark cutting was a direct response to low muscle energy and the store of glycogen at slaughter.
The optimum pH level for beef is about 5.5.
Glycogen levels in beef are affected by the nutrition stored in the muscle on farm, minus what is broken down in the pre-slaughter period.
The best way to ensure grass-fed stock is getting the right nutrition is via basic live weight gain.
“For finishing carcasses, if they gain above 0.8 kilograms per head per day, with a minimum energy of around 10.5 megajoules and pasture length of at least 10 centimetres, then hopefully they should be safe,” Dr Loudon said.
Glycogen in stock fluctuates after the pasture growing season, with different factors affecting levels at different times of the year.
“We run into things such as mycotoxins at the end of summer (rye grass staggers), and then push into mineral deficiencies, such as low magnesium,” she said.
A recent MLA survey showed 60 per cent of Tasmanian beef producers reported rye grass staggers, Dr Loudon said.
“The toxins are impacting on production, but we can’t see it.”
“We’ve reduced the risk of infectious disease and metabolic diseases and now we’re seeing the greater effects of the mycotoxins,” she said.
Mycotoxins can cause gastrointestinal disorders, heat stress and lameness, but from a dark cutting perspective they cause muscle convulsions, reduced feed intake and efficiency, which affects glycogen storage.
Dr Loudon and her colleagues ran an experiment on King Island in 2015 to survey animal management environmental factors.
Blood and liver samples were taken on farm and at slaughter and pastures sampled for mineral quality and mycotoxin concentration.
“One of the major results of our experiment was that pasture magnesium concentration was an important risk factor for dark cutting,” Dr Loudon said.
“More pasture magnesium and we can reduce the dark cutting percentage.”