Picture: Spot the difference? Free range on the right
Free range eggs are not only better they’re rounder as well. This extraordinary finding comes from scientists in the Netherlands whose research has shown that while cage eggs tend to be longer and thinner free range birds produce eggs that are shorter and wider. And, they say, their findings confirm similar results first discovered more than 25 years ago.
The new broad revelations come from the Wageningen Institute of Animal Sciences in Holland where researchers mounted a project to examine differences between egg quality and size from different systems.
They reared two hundred ISA Warren chicks to 11 weeks and then split them into two groups, one in cages and one on free range. They took eggs for testing from each group, which were both fed the same diet, at regular intervals from 25 to 59 weeks. In all they analysed over a thousand eggs for yolk colour, shell thickness, albumen and yolk weight and total weight as well as width and length.
The team discovered that the eggs from the two systems differed in a number of ways and especially in shape. Free range eggs were notably wider and shorter. When they calculated a shape index (breadth/height x 100) they found the free range eggs scored 75.44 and the cage eggs 74.7. In an article in the magazine British Poultry Science they say that the shape difference was first identified by researchers in 1981.
“A reason for this phenomenon is hard to give,” they admit, “but one might speculate that relatively wider eggs have a lower ratio between surface and volume resulting in relatively less weight loss due to evaporation. In outdoor systems layers are living under more variable circumstances and for these layers it would be advantageous to produce eggs that are less sensitive to environmental factors.”
The researchers also found that the outdoor birds began laying later than caged birds so that egg weight was lower at an early age but increased more with age than eggs from caged birds. They say that while eggshell quality decreased with age in cage layers, in the outdoor birds it remained constant or even increased. They speculate that because free range birds can walk around they may produce more effective metabolism of calcium and phosphorous in the diet.
As expected they found a marked difference in yolk colour with the cage eggs scoring 8 on the Roche scale and the free range eggs reaching 11. They attribute this to the outdoor birds eating grass and herbs.
Internally they found much more variation in the free range eggs in measurements like albumen height.
They conclude that this must be due to environmental conditions. “It appears to be more difficult to maintain a constant external and internal egg quality in an outdoor system than in a cage system,” they say. “Whether this has consequences for reproduction results or product quality (such as foodstuffs) is not clear. Factors that determine the greater fluctuation in, especially internal, egg quality need to be investigated.”
