incubation with no proper results

[mgfc27]

Hello , I have a a couple of aylesbury cross with pekin ducks , she gives me beautiful and delicious eggs every day for the second time I toke some and incubated them but is not going as well as I thought, I have a fan assisted incubator , with temp on around 37.7 celsius and humidity between 40/50% , so what really happens is that I set the eggs in there standing with the air sack up , turning is automatic (every 2 hours) and candle at day 7 and day 25 but the only thing that happen is that they pip internally and or externally (always late around day 26 or 27) and if they even come out they always have a large yolk still attached, they are all fully formed , and the sad thing is that they all end up dieing, they did one by one and I'm starting to get frustrated as I don't know if it is me doing something wrong or if the couple has some genetic problems , as I said they all pip , they all vocalise , but they all hatch with the yolk and a lot of a brownish mucus type of thing around them and end up dieing, sorry for the big text but I didn't want to miss any point . Help ?

 

[Amykins]

It sounds like they're sticky. That means your humidity is too high during incubation. :/ This is a great guide for incubation and hatching. Out of curiosity, do you ever let your broody duck hatch them naturally, or do you get the same result? Oftentimes mother nature is the best egg hatcher around!

https://www.backyardchickens.com/a/step-by-step-guide-to-assisted-hatching

 

[mgfc27]

No I didn't acually tried it yet as I'm not really sure if she does gets broody , I I'm starting to tho she has now 3 eggs and has made a lovely looking nest but still doesn't sit on the eggs :/ it is my mistake after all