Livestock dietary improvements for healthier meat
Natural supplements for cattle could lead to healthier meat with a longer shelf life.
Red meat's reputation has taken something of a battering in recent years. Dieticians have warned of the dangers of eating too much red meat, such as beef and lamb, which has been linked to increased risk of cancer and cardiovascular disease.
However, other studies have shown that red meat can be good for you (or that it's not so bad (ref 1)), It is a better source of iron than plant foods because the iron is in a more bioavailable form. Iron deficiency anaemia affects up to 1 in 20 men and 1 in 20 post-menopausal women (ref 2) in the UK but rates are much higher in developing countries.
Advice on healthier eating commonly suggests decreasing intake of saturated fats, such as those found in red meat, and increasing the intake of polyunsaturated fats, such as those found in plants, fish oils and seeds such as flax.
Polyunsaturated fats (PUFAs, for polyunsaturated fatty acids) include the long chain omega-3 and omega-6 fatty acids found in fish oil supplements that have recently been studied as potentially beneficial for preventing cardiovascular disease, inflammation and perhaps other conditions such as diabetes (ref 3) (see 'Complicated chemistry').
These PUFAs are found in red meat but at low levels. Researchers at the Institute of Biological, Environmental and Rural Sciences (IBERS), an institute of BBSRC based at Aberystwyth University, have been adding PUFAs derived from the plant extract supplement Echium oil to the cattles' winter feed to see if the amount of beneficial fish oil-like omega 3s can be increased. The oil contains a fatty acid called stearidonic acid, which can be converted (chain elongated) in the cow's liver to the beneficial fish oil-like omega-3s and then deposited in the meat and milk.
Where's the beef?
During the summer, most UK cows are fed pasture grass that is rich in precursor fatty acids; in the winter they are fed on silage. This is in contrast with the American system of rearing cattle on a concentrated feed of barley, wheat and maize all year round which results in meat that is lower in the fish oil-like fatty acids. "The pastoral system in this country gives us a better fatty acid profile than the US feed lot system — roughly double the amount of fish oils," says project leader at IBERS Dr Michael Lee. "By adding stearidonic acid we hope to improve it further," he says.
In addition to the Echium oil study, the use of more natural grazing practices has been shown to improve the amount of PUFAs in meat. Previous BBSRC and Defra-funded studies at IBERS have found that cows on pasture rich in red clover accumulate more PUFAs compared to grass, even though the amount of PUFA in grass and red clover are comparable (ref 4). In this case, an enzyme called polyphenol oxidase in the red clover reduces the breakdown of fatty acids (lipolysis) in the cow's rumen.
However, red clover is digested a lot quicker than grass and can cause a dangerous accumulation of bloat gases in rumen. "It can kill the animal," says Lee. "It used to be a problem when animals were put on high density clover pastures after winter, but now it's well controlled through pharmaceutical products."
Taste the difference
In theory, there could be an unpalatable side-effect to increasing the quantity of PUFAs in meat. Fish oils smell quite rancid because as unsaturated fats they oxidise easily. Oxidation in meat is not a good thing. This discolours the meat and makes it unsellable before it goes off. But Dr Lee has found that meat raised on pasture actually has a longer shelf life than concentrate-fed meat by four days.
The reason, Dr Lee says, is that when animals graze pasture they intake antioxidants such as vitamin A and E from the grass. These compounds prevent oxidation of the fish oils so the meat lasts longer even though it has a higher concentration of PUFAs. With a healthier fatty acid profile and a longer shelf life, Lee says the pastoral system can be a win-win situation.
The use of natural grazing systems, particularly if they can incorporate red clover, can result in a higher quality product compared to feed-lot production systems, be it milk or meat both in terms of animal health, consumer health and also extended retail shelf life. In addition if the use of Echium oil can be shown to improve PUFA composition in meat and milk during winter feeding then a system for PUFA rich meat and milk production can be adopted all-year-round.
PUFAs (polyunsaturated fatty acids), including the omega-3 fatty acids, cannot be made by the human body and must be obtained from diets. There are three main sources of omega-3s in foods: alpha-linolenic acid, a precursor found in plants, and the 'long-chain' EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) which are found almost exclusively in fish or shellfish.
These long chain omega-3s appear to have the best health benefits because people do not convert alpha-linolenic acid from plants into EPA or DHA very well. Hence, researchers are keen to increase their concentration in food, including meat and eggs because many people do not enjoy strong-tasting oily fish.
- Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease
- Anaemia, iron deficiency (external link)
- Omega-3 polyunsaturated fatty acids (PUFA) for type 2 diabetes mellitus
- Effect of fish oil on ruminal lipid metabolism in steers fed grass or red clover silages (external link)
- Dr Michael Lee, Institute of Biological, Environmental and Rural Sciences, Aberystwyth University
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- Arran Frood
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