My first hatch of 9 broody reared chicks will be 3 weeks tomorrow. In my experience that's a bit early for Marek's symptoms to show anyway, so just registering my part "in the experiment" for this season at this stage.It's usually at least 7weeks that it starts to rear it's ugly head.... whether that is the stress of being fledged, causing an initial trigger or just the time it takes to get into their system and take hold, I don't know. The most vulnerable age seemed to be about 12-16 weeks though with my previous bouts. Would be interesting to know if there is any correlation between seasons, perhaps reduced daylight or weather or just a natural coincidence that, because my broodies don't rear chicks until May/June/July, they all reach the vulnerable age in the late summer and autumn.
This first brood are not bred from my flock although they have been hatched and raised in the flock, so will perhaps act as a control sample for the concept of breeding for resistance.They are also pure bred pekins (bantam cochins), so that may also be an issue as oppose to the hybrid vigour of farmyard mutts that I mostly bred last year.
I have two other clockers sitting on eggs from my own flock, most of which will be farmyard mutts but some may be pure welsummers if they don't all smash before hatch day (sadly the shells are proving too thin for the rigours of broody setting, even with my best clocker and I'm down from 6 to 3 in the first week! )