First is the presentation of the disease itself, swollen, green shaded skin, more puss than typical bruising, and a "sour butter" smell, all indicate gangrene in quail.
This infection typically occurs when a quail has suffered an injury (flighty as they are) and the wound becomes infected. Additionally, gangrenous dermatitis can occur if the quail's surface area is overly moist and prone to bacterial growth.
Our anecdote: we had a male quail in an enclosed ground-hutch in a tropical climate. He suffered an injury on his leg and within a few days began developing gangrenous symptoms on top of lethargy, lack of appetite, hobbling/limping, etc.
Solution: 2x doses of 125mg amoxicillin per day mixed with a chicken liquid B-vitamin blend and topical application of polysporin. Within 72 hours the infection began to subside, and within 4 days the swelling began to reduce. Doses were administered via lingual syringe in morning and evening along with topical application of ointment. Treatment with amoxicillin continues until all signs of both green infection and red swelling are dissipated. Amoxicillin takes a long time to work to completion, just like in humans.
Why amoxicillin? Amoxicillin is effective in poultry at 250mg/kg and is effective at killing Gram-Positive bacteria. Gangrene in quail and Gangrenous dermatitis in poultry is typically due to Clostridium bacteria (gram-positive), and is detected through a dark green hue to the flesh of the bird and most specifically confirmed by the average farmer through its scent; spoiled butter.
Where would I find amoxicillin anyway? Pet and aquarium stores, online and brick and mortar. Fish amoxicillin can be purchased in 500mg capsules for extremely affordable prices through the commercial market. Websites such as Chewy tend to stock many different types of antibiotics, be sure you understand the type of regimen and dosage that is necessary before using them.
Why don't we just cull the male? This was the first question on our mind, and nearly occurred twice before the antibiotics did their work. We noticed the infection presenting about two days after we believe it occurred and as fragile as quail are, we quickly believed we would be culling him. The reason we went through the extra effort of treatment was due to his temperament and breeding success. This male (Texas A&M white) has as of so far given us a near 90% hatch rate on eggs, and is extremely gentle with the females. An ideal breeding bird really for the purposes of volume.
Obviously there is a never a reason to let an animal suffer, and the decision to go through the extra effort of preservation is a pro vs. con analysis, but if a bird in your flock ever presents with gangrene, these listed steps may make some difference in preserving the animal's life.
As you mention living in a tropical climate, you’re evidently not from the U.K, where Poultrykeeper Forum is based. No matter - we have overseas members and welcome their contributions about keeping birds in different conditions. So it would be interesting to know where you come from.
I think one main difference would be that it’s not possible to buy antibiotics online or over the counter here in the UK, and their use on animals is more strictly controlled than in many countries. They can only legally be prescribed by a vet, and visits to a vet would be more expensive than most people would be able to justify for an injured quail. Consequently, no, we’ve never even heard of gangrene in quails, let alone how to treat it, other than by euthanasia. I’m interested to hear that your bird recovered with the amoxicillin, well done for trying, he is obviously very special to you. I presume he’s a coturnix? They’re usually hard on the females, so a gentle one is a rarity worth breeding from. I hope he passes in his kind nature to his progeny.
Have you any photos of him? I’d love to see some. The forum software is a bit clunky, so here’s how to do it, if needed viewtopic.php?t=11259