Could you please explain how two of my pullets started laying in early December at nine months of age? I'm in the northern hemisphere so those were among the shortest fays of the year, less than 10 hours of daylight.
Genetics!
(and/or light leakage from human activity.
Why does daylight length matter in the first place?
Because the pituitary gland, responsible for releasing hormones that trigger laying, is reactive to light levels.
How reactive? It depends on the genes. And pullets are more sensitive the first year, enough to be triggered by light leakage that wouldn't impact the hens.
We all know that humans bred chickens from jungle fowl that lay only in spring, solely to reproduce... into modern laying machines that work most of the year.
What biological mechanism is responsible for the difference?
The pituitary gland.
Those are the genes we humans screwed with, in stages, over very many years.
That also explains the differences between individual birds.
Some breeds were adapted to northern Europe, laying through the long dark winter. We brought those breeds to the US, crossed this and that.
There are some breeds that quit laying in late summer. Ayam Cemani, Sumatra. Even among those, you find individuals that differ
Hatcheries are especially motivated to produce lots of eggs, so they select for traits that link to pituitary sensitivity.
I sure hope I'm not over explaining this, but it seems I didn't explain adequately the first time.
The majority of pullets will not start laying in the darkest months, not without supplemental lighting (which can be unintentional, it doesn't take a lot of light). Some can start in Jan-Feb as the daylight begins to lengthen again. But most will wait for 13 or so daylight hours.
The topic of daylight and laying has been properly studied, it's not conjecture or anecdotal. Though I'm not the sort to file away a bunch of links, I am certain anyone interested can find them (provided they have access to those sites).
Not a nice way to phrase it.
