Its is a bacterial infection that tracks up through the umbilical stump.
It then attacks one or more joints causing them to go septic and damaging the joint surfaces.
In mild cases caught early enough oral antibiotics may surfice ,in others the joints may have to be flushed some will recover some wont.
In other cases when it has gone to far the only humane option is to have the foal PTS as it will never recover to be sound or long lived.
Its also called 'septic arthritis. Its caused by bacteria gaining entry through the umbilical stump and spreads to the joints causing irreversable damage. It also goes by the name of 'navel ill'. My boys full sister had to be put down due to it and what really made me angry was the fact that she was foaled at the stud where the stallion was standing
I purchased a mare years ago that had previously lost a foal to joint-ill and had always thought it was down to hygiene, or lack of it after the birth. Over the years my ears have always pricked up when this is mentioned to add to my knowledge base.
Studs are very aware of this potential danger and I would consider that they do everything in their power to prevent it. I am still not clear if it can be prevented or not, it is a very sad situation and distressing for everyone concerned not least the poor mare loosing her foal.
It's basically septicaemia and can enter the foal through pretty much any orifice although normally through the umbilicus.
Thinking these days is that often there is a problem with the foal suckling in those first few hours - they don't get enough colostrum which in turn weakens their immunity.
It's a very sad thing and can happen to anyone even if you take the very best of care.
my sympathies to them, it's really hard to treat because the joints are difficult to get anti biotics into.
We've had two with it, one survived after £1300 of treatment, the other sadly died at around two weeks after getting it.
When we did a post mortem I was shocked to see it's shoulder was pea green with gunk inside.. The original first signs had been a slight lameness in front, barely anything, and we got the vet out asap. Even then it was too late.
We had pumped anti -b in several times a day , flushed the knee joint out where the infection started, but it just took hold and we had to euthanise.
Although we always try to spray the stump soon after birth ours often foal outside and it's an hour or so after when we find them.
Even spraying soon after birth doesn't always protect them I'm afraid.