Low hatching temp for large eggs?

[LaurenRitz]

I had a really bad hatch this week. Out of 16 eggs, only 7 hatched, and one of those hatched late and wasn't able to survive. I'm not sure yet about another.

Half of these eggs were pretty large, and only two of the large eggs hatched.

I went back through my notes, and while I haven't recorded actual egg size I did learn that my Marans and MaransX (extra large eggs) have hatched less than a quarter of the set eggs.

I was doing some research online and found one article from a professional hatchery that talked about this. It said that large eggs hatched at the normal temperatures hatch at lower rates because as the chicks fill the shell they can't shed heat as well. They overheat in the last ten days of incubation and can't make it to hatch.

When they hatch large eggs, it said that in the last ten days they gradually reduce the temperature to 99.1. It was very gradual, which my incubator can't handle, but I was thinking about doing a test.

Extra large eggs only, as defined by "eggs that don't fit in a standard carton," set at 99.5 until day 12, then reduced to 99. I would expect a bit of a late hatch.

I would also check the temperatures of the eggs daily. I suspect that any eggs that are overheating would be pretty obvious.

 

[MysteryChicken]

At lock down I reduce the temperature to 98.5°F since they can produce some of their body heat.
Lockdown can start at the16th, or 18th day.

 

[LaurenRitz]

Ok, so already an anomaly. I keep my hoise at 77 f during the winter. I measured the temp of the eggs, and two of them are maintaining a temperature at least 3 degrees above the others. Most eggs are between 63 and 65, these two are stubbornly over 68. And one of them isn't a large egg.

All of these eggs are less than a week old, stored in exactly the same conditions.

 

[LaurenRitz]

At lock down I reduce the temperature to 98.5°F since they can produce some of their body heat.
Lockdown can start at the16th, or 18th day.

Thanks. I've thought about doing that in the past but wasn't sure how it would affect the chicks.

 

[MysteryChicken]

Thanks. I've thought about doing that in the past but wasn't sure how it would affect the chicks.

It a positive affect. I do it for all sized eggs, including duck, & goose.

 

[LaurenRitz]

12 eggs for the test, all large or extra large (meaning they wouldn't fit through the holes in the turner tray of my incubator). All eggs are less than a week old. They will go around the outside of the incubator to avoid location discrepancies.

4 MaransX (she lays nearly every day and laid through the winter).
1 dark pink/brown
1 medium brown
2 Ranger, long and slender
4 lighter pink

99.5 for the first 12 days
99 from day 12 until lockdown
98.5 at lockdown.

 

[LaurenRitz]

Day 18 (incubator countdown): the temperatures ranged from 97.9 to 100.6. The highest were one of the Rangers (100.6) and the pink (100.4), but the Marans crosses were all in the 99 degree range.

The Ranger and the pink were right next to each other and were in dappled light from the window for a few minutes.

 

[LaurenRitz]

Day 16 (incubator countdown): take into consideration that these temps are taken at different times of day (early morning in this case), with a handheld thermometer so at varying distances.

Temps range from 94.8 to 97.3. I candled and there were two clears and three that I couldn't see. The clears were right in the middle of the pack, temperature wise. The highest temperatures were two of the MaransX.