Why do Chickens Lay Different Coloured Eggs? November 05 2015
It is strange but true that people think that eggs with brown shells are healthier than eggs with white shells. Indeed some people even believe that free range chickens produce brown shelled eggs and battery chickens lay white shelled eggs.
However eggs from chickens can come in a variety of colours – they could be white, cream, brown, blue or green. Egg colour is determined by the genetics of the hens. A Maran will lay a really dark brown egg; a Leghorn will lay a white shelled egg; an Ameraucana chicken lays blue eggs. An interesting coloured egg is produced by crossing two different breeds of chicken - one breed which produces a dark brown coloured shelled egg and another which produces a blue coloured one. The result of this is the Olive Egger - the shells of this chicken are olive, sometimes dark olive and sometimes a lighter olive, depending on the egg cycle of the chicken. Interestingly if you look at the chicken’s ear lobes and spot that they are white, that chicken will lay white eggs.
All eggs begin as white. The ones that are a different colour become shaded as they travel through the hen’s oviduct. Pigments are deposited on the eggs as they go through the oviduct and it takes about 26 hours to complete that journey. The shell itself takes about 20 hours to complete. The chickens that lay brown tinted eggs have the pigment protoporphyrin deposited on the eggs but the pigment is deposited late in the shell forming process. This is the reason that the pigment does not penetrate the interior of the egg and just colours the exterior, the surface of the egg. So brown tinted shells are brown on the outside and white on the inside. The Ameraucana hens have the pigment oocyanin deposited early on in the shell producing process – this is why the blue is on the exterior and interior of the shell. With regards the Olive Egger, the brown pigment goes on the top of the blue pigment, making an olive green coloured egg shell. The darker that the brown pigment is, the more olive coloured is the shell.