Yeah, the blue marks on the egg are "feather fluff tracks".
Silly old Shadrach. He thinks the marks are from Blue-Kote inside the vent.Err no.
Silly old Shadrach is aware that the marks are likely to be from feather contact on the egg.
Allow me to explain.
Of course, you will know the the vaginal wall of a hen is mobile and the hen can push the vaginal wall out through her vent some considerable distance, over an inch would be my guesstimate from the last time I saw this. You will of course know this from watching your own hens abort the sperm from an unwanted mating.
No doubt you've watched a hen lay an egg by somehow squeezing your head into one of those dark little nest boxes in your coops. Perhaps not but you're bound to have watched a video on the Internet.
I won't bore you with the complete sequence but the two pictures below should be adequate to make my point; which was, for those of you with short memories and itchy keyboard fingers, that I prefer to use water only for cleaning around a hens vent because of the risk of chemicals that may be suitable for external use being introduced into the oviduct.
So, when a hen lays an egg the vaginal wall gets pushed outwards as well as sideways as the egg progresses the length of her vagina. The egg is pushed out in a pulse motion, each pulse extending the vaginal wall. At a point just past the first picture there is a considerable amount of the vaginal wall now exposed to the outside environment and as you can see may come into contact with the eggs that she has organized beneath her, often by shuffling her rear end maneuver them into position. In this shuffling the eggs any chemicals around the vent area and the local feathering may get transfered to the eggs below.
Once the egg has left the hens vent, the vent doesn't snap shut like a spring as the next picture illustrates. It can take up to 20 seconds (usually less from my observations) for the hens vent to retract her vagina and the vent shape return to normal. Some hens I've observed tend to squat on the eggs below while the vagina retracts. Once again anything that is on the surface of the eggs may come into contact with the retracting vagina wall and end up inside the vent when retraction is complete.
You will have noticed that when a hen goes to lay an egg, one of the things she does while arranging any eggs below is to make sure the upper surfaces of the eggs are clean by either removing stuff like straw with her beak, but more often by polishing the tops of the eggs with what I describe as a belly, or bum shuffle.
There are chemicals, particularly astringents, some steroidal creams, Hydrogen peroxide, Betadine and others that are meant for external use only. My view is it is better not to risk such chemicals entering the oviduct.
Of course, you all know all this so I've probably wasted my time typing this out and providing a couple of pictures.
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