STAFF |BRANDON, MAN.
Beef researchers hoping to emulate omega-3-enriched pork, poultry and eggs by adding flax to cattle diets are finding it’s easier said than done.
In order for beef marketers to slap a Health Canada approved label on beef touting it as a source of the “good” fat that helps prevent heart disease and stroke, the meat must contain 300 milligrams or more of omega-3 fatty acids per 100-g serving.
“Previous research on flax-fed beef found that if you supplement cattle with flax, you get really significant increases in omega-3 fatty acids,” said Hushton Block, a beef researcher at AAFC Brandon.
“But we had problems getting the levels high enough to meet the standard, and doing it consistently so that you don’t have to test every animal as you send it for slaughter.”
That’s because unlike monogastrids, ruminants don’t do well on high-fat diets. That means there is a limit – about six to eight per cent – to how much oily flax meal can be added to the ration without disrupting rumen fermentation.
Other trials under feedlot conditions, where flax meal was added to a high-grain diet for 60 to 100 days, have been successful in boosting omega-3 levels, but the results were either inconsistent or the amounts fell short of label requirements.
“If we want to increase this, we know we can’t feed more per day, but we could feed it for a lot longer,” said Block.
To extend the feeding period, Block’s research team opted instead for a high-forage diet with six per cent added fat over 250 days.
The control group was fed hay and barley, while the test animals got hay and a flax-barley
blend made in a hammer mill, as well as Linpro, a commercial blend of extruded flax and
pulses such as field peas and lentils. Estrus-suppression drugs were added to control the five heifers in each group.
Feed intake was a problem with some animals. Early on, one heifer refused the ration and was taken out. A second animal reduced her intake, but was so close to the end of the trial that she was kept in until slaughter. The stress left her a dark cutter, Block noted.
That could present a problem, he added, because under feedlot conditions, such animals would be very difficult to spot.
“You could have erratic results under a large-pen feeding scenario.”
But overall, there was no effect on feed intake, which averaged 10 kg per day. Average daily gain was 1.1 kg per day, with a feed conversion ratio of 9:1, which was “not bad” for a forage-based diet, compared to 6:1 for feedlots. Slaughter age
was 18 months.
University of Manitoba researchers conducted sensory testing and found that there was no effect on beef aroma, flavour, tenderness, or connective tissue.
“I was terribly concerned that if we fed these animals lots of flax and actually managed to change the fatty acid profile that we would end up with a steak that tasted like flax oil,” said Block, who added that the ration seemed to only to have a minor effect in terms of reduced juiciness.
Off flavours were present at “trace” amounts, but no fishy smell was found.
CLA levels rose as expected due to the forage, and omega-6 fatty acids were unchanged.
Omega-3 levels in backfat saw a “favourable” two-fold and three-fold rise, but generally fell short of the target.
On the other hand , Block said the “exciting part” was the spike in vaccenic acid levels, another beneficial fatty acid. Further study of this is planned.
In lab rat studies at the University of Alberta, supplementation with vaccenic acid for three to 16 weeks at a dietary rate of one to 1.5 per cent was found to reduce plasma triglycerides, lower total cholesterol and other harmful compounds.
Conventional feedlot beef is typically very low in vaccenic acid, and amounts in the control group in the Brandon study were low even on a forage- based diet.
“When you go to our flax-finished groups, we’re getting somewhere in the range of eight to nine times of what was present in the control,” said Block. “That’s a huge increase that has beneficial health implications for the consumers of beef fat.”