Are you willing to do an nercopsy? There's really not other way of knowing unless you open the birds up.
If it were a worms problem your hens would probably have chronic diarrhea and be very skinny. I know chicken worms exist, but I think they're regional. I've NEVER seen chicken worms, personally, having kept birds in Idaho and Montana. But I know folks in warmer/wetter climates can struggle with them.
The main cause of early death I've had in hens is internal laying; there can be almost no symptom or there can be a long, steady decline of the bird. Basically there's holes in the hen's reproductive tract and yolk drop down into the abdomen. It's harmless to the hen until the yolk starts to become infected, then the infection kills her.
I've had hens lay intermittently and last 3-4 years with internal laying. I've had pullets die from it before they ever laid their first egg. I've had hens drop dead on me and I didn't know what happened until I opened her up. I've had hens obviously battling the IL infection for months or more before dying.
Did you notice any sign of respiratory distress or limping in the birds before they died?
Things to look for if you suspect a hen is laying internally;
- yolk in the feces or egg-smelling feces
- saggy/squishy/distended abdomen
- if battling infection; lethargy, blueing of the comb/wattles, labored breathing
- a dead hen; rotten egg smell and/or yolk-like discharge from abdomen (if you open her up you'll find the rotten yolk in her body cavity)
It might not be that! But that does happen. I've had most of my IL deaths from hatchery stock and production birds; I've probably lost 12-20 hens to it. Of my 'rare breed' and non-hatchery birds, I've only ever lost 1 or 2 to IL. Out of hundreds or thousands of birds over the years.
Other things I've lost hens randomly to:
- bad genes; I had one awesome hen drop dead on me. She was a red ranger/marans cross. I opened her up and her entire body cavity was PACKED with fat. Her heart and chest, her abdomen. She was a fat football. That's what I get for crossing a meat hybrid I guess. All ofm y red rangers died before they were 4 years old, the breed wasn't long lived.
- egg binding; I've only seen it once out of hundreds of hens, but I did have an Ameraucana die on the nest egg-bound once. Poor girl, I didn't find her until she'd already passed
- I haven't lost a bird to mites, but I've come close. Mites/lice can infest a chicken whose immune system is poor or who doesn't have access to dust bathing, and you won't know anything's amiss until the chicken is nearly dead from blood loss if you haven't been watching your birds for signs of infestation. It can escalate very quickly! Look under the feathers at the skin for egg clusters and tiny bugs. DE in the dust bath works great for this; also letting them bathe in
wood ash
- Old age; my oldest hens have died around 8 years old
Also; most poultry/fowl diseases are species-specific. There are a "couple" rare exceptions which are mostly found in industry/factory settings where millions/billions of sickly birds are sharing the same soil. If your chickens are dying and not the ducks, I wouldn't worry about it, personally. I've kept all manner of fowl together in the same flock and personally have never had a problem. I'm sure there are people out there who have. But in my
experience, it's usually NOT some kind of contagious disease. Usually.
