Hens that range lay eggs with improved nutritional qualities, according to new research in America.
The findings reflect long-standing results in this country which have demonstrated marked differences between cage eggs and those from birds which range.
Researchers at the Pennsylvania State University found that pastured birds produced about three times more omega-3 fat in their eggs than did caged birds fed a commercial diet. The range eggs also had boosted levels of vitamins A and E, the team found.
The research was led by Heather Kirsten, Assistant Professor of Crop Production and Ecology in the University’s College of Agricultural Sciences and Paul Patterson, Associate Professor of Poultry Science.
The team housed 25 hens in a mobile coop and allowed them to feed for two weeks at a time on grass, red and white clover and alfalfa. During each rotation, eggs were analysed for levels of unsaturated fat and vitamins in their yolks. The findings were compared with eggs laid by birds in cages on what the research teams call “a typical grain diet”.
As well as the tripled amounts of omega-3 fat they also found about twice as much vitamin E and 40 percent more vitamin A in the yolks of pasture-fed birds than in the caged birds.
“The longer the birds were on pasture, the more vitamins they produced,” says Kirsten in a report published on the University’s website.
The team also found variation in pasture produced changes in nutrient content.
“On average the mixtures highly dominated by legumes—clover and alfalfa—produced 18 per cent more omega-3 fat than grass alone,” Kirsten says. Eggs from the alfalfa pasture had 25 per cent more omega-3 than grass-produced counterparts. “In absolute amounts, this was not a very big increase,” says Kirsten. "But with more research and some different feeding regimes, it might go higher.”
The team had previously established that some plants, like alfalfa, have higher levels of available omega 3 than others.
“From this study we confirmed three nutritional advantages of raising hens on pasture as compared to on an industry diet in cages: the increases in omega-3 fatty acids and in vitamins A and E. We also found that differences in omega-3 levels in plants have an effect on the eggs.”
In Britain a Ministry of Agriculture project in 1973 found that amounts of vitamin B12 in eggs from ranging hens were 70 per cent higher than cage eggs and amounts of folic acid were 56 per cent higher.
The eggs laid by birds on pasture scored higher in 17 of the 19 categories tested.
A second project in 1988, funded by the British Egg Industry Council, found levels of B12 were 41 per cent higher in eggs from ranging birds and folic acid content was 17 per cent higher. Four years ago a test of eggs bought from supermarkets found that the B12 content of free range was 25 per cent higher than cage eggs.
The 1973 scientists concluded that the B12 and folic acid differences were “significant” and “important”.
“Eggs are good sources of B12 and folic acid,” they said, “and it is of importance that these two vitamins showed the greatest variation between management systems.” They stressed that the difference “would be measurable” for those who depended on eggs as an important source of these nutrients.
B12 is the vitamin that many doctors say vegetarians have most difficulty in obtaining because it occurs only in foods of animal origin and eggs are one of the few sources for those who do not eat meat or fish.
These results have never been widely publicised. They first appeared when the interest in vegetarianism and food quality was minimal and when the importance of free range was at an all time low.
One expert commented: “There is a difference between free range and intensive eggs. In the past the stock response to this has always been that for those eating a properly balanced diet the difference is not significant.
“But of course the numbers eating that kind of balanced diet has changed dramatically. There are now not only large numbers of vegetarians but many others who have reduced the amounts of meat and animal products they eat.”
