the solution to the "every chicken drops dead all at once" problem:

[Senor Smoke]

the problem with it is that a dirty pen doesn't cause all of the animals to drop dead at the same time with no warning. assuming that you *are* cleaning the pen and that you just have more chickens than you can keep up with, chickens dying from filth *should* be a self-correcting system. the filth builds up too fast, then the weakest chickens of your flock die off causing the flock to produce filth slower & over time it corrects down to the level you can deal with.

the solution then is to code the chicken's reaction to filthdeath to sort of recreate this system in a similar way that panic cures boredom. for example you could make it so that when a chicken dies from filth all of the other chickens in the flock have a 90% chance to have their filthdeath progress reset to 50 but gives them a stacking moodle that only decays at all when their pen is *completely* clean, and that moodle reduces the chance and the effect of the filthdeath forgiveness mechanic by half (first chicken drops dead 90% chance to reduce the other chickens to 50 progress if higher, second chicken to die has a 45% chance to reduce the others to 75 if higher, ect)
of course you'd have to fiddle with the numbers here but this would recreate what the players expect of their flock; one bird dies as a canary in the coalmine, then two or three die at once to indicate that they haven't fixed the problem adequately, then the flock starts actually dropping. but in between those stages the player has a chance to go "oh no my flock is dying from the filth" and clean it