Foal season is upon us, and it is expected to have sick foals. A common problem that newborn and young foals experience is joint ill caused by a variety of reasons. A common misconception of a lame foal is that it was caused by trauma generally blamed on the mare. The rule that all horse owners and veterinarians should live by when it comes to lame foals is that it is a septic joint until proven otherwise. The goal of this article is to discuss the risk factors for joint ill on foals, clinical signs of joint ill and treatment options.
Joint ill is more a horseman’s term for septic arthritis and/or septic physitis in newborn or young foals. Septic arthritis is a bacterial infection of a joint or joints leading to inflammation, heat, pain, swelling and cartilage injury. The biggest question that many owners want to know is how did the bacteria make its way to the joint in the first place to ultimately prevent it from happening. Well the reason is just like all newborns: foals do not have a developed immune system and rely heavily on consumption and intake of antibodies from the mare’s colostrum. Without adequate intake and absorption of antibodies from colostrum, foals are at high risk of sepsis. Remember that there is a narrow 24 hour window that the gut of the foal can absorb the large antibody proteins before the gut closes. Without these very important antibodies, foals are wide open to infection from any form of bacteria from its environment. Foals that do not receive adequate amounts of antibodies from colostrum are called FPT or failure of passive transfer.
A common area that is blamed for the entrance of bacteria in a foal is through the umbilicus, which is a very important potential source but not the only pathway into the foal. Bacteria can enter the foal through its lungs and gastrointestinal tract as well. It’s thought that if the foal is able to absorb colostrum they are also able to absorb bad things like bacteria through their gut wall. If you have witnessed a newborn foal searching for its first meal then you can appreciate how a newborn foal is exposed to potential pathogens almost immediately after birth and also how frustrating it can be to watch. While searching for the udder, they commonly nurse on other areas of the mare and also on objects in the stall like feeders, walls and buckets.
Once the bacterium enters the blood stream, there are several possible outcomes. (1.) The bacteria are cleared from the blood stream by means of white blood cells and antibodies and no further harm is done. (2.) The foal becomes septic from the bacteria in the blood and quickly becomes ill. (3.) Low levels of bacteria enter the blood and become deposited on small blood vessels near the foal’s joints. If the foal does not have adequate antibodies from colostrum, it is easy to see the foal is very susceptible to infection.
There is unique blood supply to the growth plates (physis) and other parts of the bones that make up the joints in the foal. The theory is that blood will sludge or slow in these small blood vessels and with the unique loops that the vessels make creates an ideal place for bacteria circulating in the blood to be deposited and start infections. There are several areas that infection can set up shop in around the joint and can lead to infection of bone (osteomyelitis) or infection of the joint structures (synovitis). These different types are as follows:
S-Type – Synovial infection (inside the joint)
E-Type – Epiphyseal osteomyelitis (part of bone nearest the joint)
P-Type – Physeal osteomyelitis (at the growth plate level)
Read more in the February 2020 issue of Oklahoma Farm & Ranch.