Here is a couple of articles by the research group of Cesare Castellini, Alessandro Dal Bosco and Cecilia Mugnai. They've been working a lot on organic and free range poultry systems, maybe you can ask them directly for mor information.

Hope this helps.

There could be a minor difference in the internal quality of standard and organic/free range eggs depending on the breed and feed consumed by the hens. Eggs from free range usually have a darker yolk color because of access to green forage, containing relatively higher Carotene, precursor for vitamin A in them making these eggs more acceptable by consumers. Regarding external quality, the egg shell from free range hens is often stronger than eggs from caged layers because of free access to limestone while foraging. making such eggs lees prone to damage upon processing and transport.

In addition to the A. Beker answer above, free range eggs tend to have higher vitamin D3 due to greater exposure to sunlight.  They, also, have 2-3 times more natural omega 3 from their foraging diet.  Omega 3 in caged layer eggs can be boosted by adding fish meal or flax seed meal to their feed.

Eggs produced from free range system vary a little from those produced form cage system since under free range the bird consumes variety of proteins including turmoids and expected to have better yolk colour intensity, higher vita content and stronger shells thus less prone to breakage. thus naturally fetches premium price

Thank you for your various answers, i was curious because I have noticed that free range eggs cost a lot more than conventional eggs. So I wanted to find out if the logic of these high prices lied on their exceptional quality or just exceptional marketing strategies? To me, it appears that the only benefit that free range eggs have is the darker egg yolk which subsequently leads to higher vitamin E and egg shell quality. I just find it senseless for consumers to pay more for a darker yolk that could also be achieved by conventional egg producers through the addition of xanthophylls. Leonardo I will give those papers a look and maybe they could provide more insight.

Mr. Mabusela, the higher price for eggs from free range layers is related to some of the following factors: Free range birds are frequently exposed to disease causing organisms, wild birds and therefore management cost to raise them is higher, so does their product. Secondly, the number of eggs laid by hens in free range per production year is lower than hens under the conventional system (some consumers preferre free range eggs than caged/jailed hens eggs) costing more to the producer that results to higher price.   

thank you Ali Beker, i think more research needs to be focused on the perception of consumers with regards to free range eggs and conventional eggs. some consumers seem to willing to pay more money for free range eggs, i am not sure if they think free range eggs have better quality than conventional eggs or because they believe in chicken liberation :).

Mr. Mabusela, I think in places where food availability is scarce, there is not that much emphasis given to food quality. Food availability and price are the most important factors. However, in some developed countries where there is plenty of food available, some consumers give emphasis to food quality and animal welfare.

That's very true Ali, food insecurity is a monumental problem, particularly in undeveloped countries and it becomes hard if not close to impossible to be thinking about animal welfare when people are starving. Some people want to adhere to good welfare standards but they just cannot because it becomes too expensive to run free range.