Hi! I'm sorry that happened. It could be a couple things. If she had poop stuck all over her bum, it could have stopped her up, caused an infection. Fly strike would be rare during the winter. Worms and runny poop can cause it. Have you dewormed? Can you clean off her bum with water and have a look for infection or injury?
always good to keep an eye to be sure all butts are clean. It;s easy to soak off dried poop with warm water. I'd check the rest closely, maybe deworm.
Ok thanks. All of my chickens haven't laid for about 2 months and wondered if I find any more chickens with the same symptoms should I start antibiotics. If so what kind and how much should I give them.
I agree the two main causes of diarrhea are Coccidiosis (which the Corrid will treat) and worms. Antibiotics won't help if it is worm or parasite based.
Worms tend to cause birds to go off laying, look thin, become lethargic, pale combs, then dehydrate with diarrhea and slowly starve from lack of nutrition (which the worms are stealing). Being run down from worm overload leaves them vulnerable to other illnesses and conditions.
Coccidiosis will also cause lethargy, usually first in the form of sitting fluffed with eyes half closed. Diarrhea may be merely thinner normal poo at first but then have bright red blood (not to be confused with the stringy rosy pink gut lining that is normal shed). Not all infections of Coccidiosis will produce bloody poo as it depends on where the coccidia have taken residence in the digestive tract. Coccidiosis tends to move quickly in progression with the bird going down quickly after bloody poo is seen. Coccidia is not likely during the winter months unless you live in a warm, moist climate (where they can thrive) or have a lot of spillage under a heated lamp.
I would check all birds for symptoms of runny poo, worm as a matter of fact, and consider putting Corrid in the water as follow up, or you may simply put all of them on medicated (Amprolium) based feed as a precaution.
From what you described with finding just the one bird, I would also check the dead hen very closely for Vent Gleet. That can produce horrendous looking poo/sludge from the vent that is very smelly. The vent will usually look red and swollen as well. Vent Gleet is a yeast overgrowth in the vent and is not contagious, per se, as it tends to affect individual birds. It can be passed from one bird to another through the rooster, but generally it is brought on by being run down, usually from worm overload or general stress, which can happen during harsh weather months. For flock wide treatment, yogurt mash and apple cider vinegar in the water can help a lot to improve gut balance to fend off yeast overgrowths. You can also buy probiotics at the feed store to place in the water. If you see other birds with suspicious vents, clean, then spray with an antifungal spray like Tinactin, treating with the yogurt and apple cider vinegar. That will rid most mild infections if you stay with the regiment for a good week or two. For serious infections, you will need antifungal meds like Nystatin from the vet.
The only way to know for certain what took the hen is a necropsy, but as many don't want the expense or bother, a broad based approach for the rest of the flock can head off flock wide crisis.
It is important to know that sometimes a bird will go down with something that never affects the rest of the flock (being an internal cancer or such). You simply continue to do good maintenance for the flock.