By Marianne Curtis
FEEDING cows to produce milk enriched with human health-promoting fatty acids, known as conjugated linoleic acids (CLAs) is the objective of a project beginning at Reading University this autumn.
The three-year project, conducted in collaboration with Southampton University will examine what levels of CLAs are required to boost human immunity, explains Reading University researcher Chris Reynolds.
"In the first 18-month phase of the project, dairy cows will be fed different oils and other factors with varying forage/concentrate ratios and different forages.
"It is already known that grazing cows produce twice the level of CLAs in their milk compared with cows on a winter diet, so we will examine how milk CLA levels can be boosted using rations fed to housed cows."
Although feeding fish oil increases milk CLA levels, this route is problematic, says Dr Reynolds. "Fish oil depresses milk fat and there are environmental concerns over the use of fish products. Taint of milk and milk products is also a worry."
The objective of this part of the study is to enhance CLA levels economically without compromising cow health or milk quality, he adds.
CLAs occur in different forms, which have various health benefits (see panel). The good news, as far as the ruminant livestock industry is concerned, is they only occur at significant levels in ruminant meat and milk (see table). "But finding ways of producing consistent levels of these compounds in milk is important before any marketing claims are made," says Dr Reynolds.
However, in the future it may be possible to market enriched milks and dairy products along similar lines to products such as Benecol, a sterol enriched margarine which is said to reduce cholesterol levels, he explains.
"Although we cannot predict how much producers would gain from this, there is great interest from the industry and I have producers queuing to feed diets which will enhance milk CLA levels."
The project aims to find out by how much milk CLA levels can be increased and what levels are required to give human health benefits, says Dr Reynolds. "Initially, people taking part in the project will be given different forms and quantities of CLAs in capsule form at Southampton University.
"Evidence from animal experiments indicates that they allow the body to respond to infection while minimising negative effects associated with fighting disease, such as fever and weight loss."
Once the Reading University team has worked out how to successfully boost milk CLA levels, people taking part in the experiment will be given CLA-enhanced milk rather than capsules and researchers will again measure their immune response. *
Chris Reynolds hopes to see some beneficial effects of CLAs in milk on the human immune system.
BENEFITS OF CLAs
• Enhance immune system.
• Reduce artery hardening.
• Reduce fat deposition.
• Enhance bone mineralisation.
CLAs in animal products
Food CLA (mg/g fat)
Beef mince 4.3