OTTAWA — It can be a considerable economic loss when a beef carcass is discounted because the muscle is a dark red or purple colour.
Known as dark cutters, these carcasses are automatically graded as B4 and end up as ground beef because the meat is too dark and tough.
The accepted cause of dark cutting is insufficient muscle glycogen to reduce post mortem muscle pH.
Shahid Mahmood, a PhD candidate at the University of Alberta, is among a group of researchers who have found distinct correlations between dark cutting and weight gain, gender, temperature fluctuation, implant programs and rough handling.
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The incidence of dark cutting has increased in Canada from .8 to 1.3 percent.
Mahmood’s research is following thousands of cattle from Alberta feedlots to the slaughter plants.
Heifers appear to be more susceptible, he said in an interview at the Canadian Meat Council’s annual meeting, which was held in Ottawa Sept. 27-29. The meat council presented him with a scholarship to continue his work on meat quality.
Some producers feed MGA to heifers to suppress estrus and encourage growth. This product has a withdrawal period of two days before slaughter. The effects of the hormone wear off if there is a delay between shipping and slaughter. If this happens, females start to cycle and their behaviour and physiology changes.
“Once they start to change the cyclicity, they will be very aggressive, they won’t eat, they won’t drink,” he said.
Other risks include cattle that gain less weight than their pen mates, nervous animals, stress from wild temperature fluctuations and poor handling. Heifers frequently experience the most stress.
“One study has shown heifers are more susceptible to heat stress compared to steers, so it means you need to take extra precaution for heifers when you are handling them in those summer months,” he said.
Cattle that have low average daily gain are also at risk.
“The problem is not carcass weight. The problem is their growth rate,” he said.
Feeding regimes also contribute to carcass quality.
“In this study, the cattle that were grass fed before finishing at the feedlot were less likely to cut dark compared to those cattle that were backgrounded,” he said.
He and other scientists have also looked at the use of hormone implants and beta-agonists such as Optaflexx, which did not appear to contribute to dark cutting.
“It will reduce the likelihood of Prime and AAA if you use Optaflexx,” he said.
“It reduces the marbling in the muscles, but we did not find it increased the incidence of dark cutting.”
- mixing of unfamiliar cattle (especially bulls or stags) several hours before slaughter
- heifers that are in heat and riding other cattle
- cattle that have been switched from a high energy to a low energy diet shortly before slaughter
- cattle that have been off feed or water for too long before slaughter
- cattle that are held at packing plants over the weekend before slaughter
- aggressive implant regimes
- temperature stress
- some breeds or bloodlines may have a higher incidence of dark cutting, but the role of genetics is generally believed to be minor compared to environmental and management factors
- absence of electrolyte therapy at slaughter plants
