Infertile egg or fertile egg?

[Conolii0316]

I was a little concerned that my duck eggs weren't fertile. But I spotted an air sac on the bottom of the egg by candling it. Can infertile eggs have an air sac too? Because I want to know if my eggs are fertile...

 

[Yorkshire Coop]

All eggs have an air sac if they are fertile or not. If you left an egg on the counter and candled it as the days went on it would naturally lose moisture through the pores in the egg and the air sac would grow larger. To check for fertility you will need to crack some eggs open and check for the bullseye or donut on the yolk. Have you started incubating the eggs? The air sac should be at the fat end of the egg.
Her are some pics of fertile eggs

 

[Conolii0316]

I've put the eggs in the incubator for 3 days now. I've got a humidity of 45%~55% inside the incubator, so I think the air sac is not from the lack of moisture. I am hoping the tiny air sack in the egg is a good sign of development.

 

[Yorkshire Coop]

Yes it's a good sign. Once they are further along in incubation you should be able to see development in the egg this will then tell you if they are fertile or not. Here are some duck egg candling pics for you to compare against. At 3 days you might not see a lot in the eggs yet. https://www.backyardchickens.com/t/304863/duck-egg-candling-photo-diary

Good luck with your incubation

 

[Conolii0316]

Thank you for the very useful information! I cannot wait to see the veins growing out inside the eggs

 

[collingwood]

Welcome to BYC!