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What causes blood spots in eggs?
Blood spots are also called meat spots. Occasionally found on an egg yolk. Contrary to popular opinion, these tiny spots do not indicate a fertilized egg. Rather, they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg or by a similar accident in the wall of the oviduct. Less than 1% of all eggs produced have blood spots.
Mass candling methods reveal most eggs with blood spots and those eggs are removed but, even with electronic spotters, it is impossible to catch all of them. As an egg ages, the yolk takes up water from the albumen to dilute the blood spot so, in actuality, a blood spot indicates that the egg is fresh. Both chemically and nutritionally, these eggs are fit to eat. The spot can be removed with the tip of a knife, if you wish.
Blood spots are more commonly found in brown eggs. The reason is two-fold. Firstly, the genetics of brown birds predisposes them to lay more eggs with blood spots in them. Secondly, during the candling procedure, the brown shell of the egg appears to have a red tint to it, which makes the task of looking for a red spot behind it extremely difficult.