Updated: Mar 23, 2021
What Does Laminitis Mean?
Laminitis is described as inflammation in the lamina of the corium. The consequence of this inflammation is separation, and can be chronic or acute. It can be seen on radiographs as either "rotation" or "sinking" of the coffin bone, sometimes accompanied by gas tracking. In it's acute phase, it is also known as "founder". In the more chronic or long term laminitis the dermal and epidermal lamina "let go" of each other and the resulting gap is filled in with material known as the lamellar wedge. The recovery time of this condition is usually about one year, depending on the type of laminitis, the severity of the sinking, and the level of destruction of the lamina. It is a long process, and it can be hard to watch as your equine friend is suffering.
Why does this separation occur?
While the exact science is still debated, it has been agreed upon that there are several triggers, and as far as I know there are two categories of laminitis. There is hormonal laminitis, and there is laminitis caused by systemic inflammation.
Systemic Inflammatory Disease Induced Laminitis
Systemic inflammation laminitis is often referred to as systemic inflammatory disease, or SID, it is also described as systematic inflammatory response syndrome, or SIRS. In SID-induced laminitis, the basement membrane of the lamina is damaged and causes the dermal and epidermal lamina to completely let go, creating an acute sinker. In an SID event, there can be permanent damage done to the lamina, which can cause issues with lamellar connection once the event is over, as well as bone density. When blood perfusion is limited, it can starve parts of the bone causing bone loss and/or remodeling (ski-tipping). This is one reason it is crucial to mark the hairline and measure the CE in radiographs, it helps to determine the extent of the sinking and the outlook for recovery. Up until recently, enzymes known as matrix metalloproteinase, or MMP enzymes, were blamed entirely for the damage. It was thought that MMP enzymes alone destroy the attachment of the basement membranes of the lamina, and once these basement membranes have been degraded, the dermal and epidermal lamina let go of each other and separation occurs. Now, we are seeing that there are proteins (ADAM and ADAMTS) and regulators involved in an earlier period of the SID event that are also involved in the destruction of and the eventual failure of the lamellar connection. Dr. Debra Taylor (DVM, MS, DACVIM) suggests that we move away from naming the MMP enzymes alone, and instead call these "laminitis trigger factors". However, as far as I know, the MMP enzymes are still at least partially involved in basement membrane destruction, so if you name the MMP enzymes as the cause, I think we will all be able to understand that you're talking about the SID induced laminitic event, and not hormonal laminitis.
So, what causes this SID-induced laminitis, what are the trigger factors? SID laminitis can be triggered by eating a toxic plant, reaction to vaccines, carbohydrate overload (breaking into the grain room and binging), bacterial infection, diarrhea, high fever, pneumonia, a severe allergic reaction, etc. This is can be a one-off event that can be controlled by removing the offending toxin, or you will need to aggressively treat the underlying disease with medication, and support the horse's immune system. Due to the severity and possible permanent damage to the lamina, SID event laminitis can be much more devastating to the lamina than hormonal laminitis, and as such the recovery outlook can be more grim. Measuring the CE can give an idea of the rehab outlook, the larger the CE, the longer and more painful of a road it will be, however this is not to say that you shouldn't try. The following treatment protocol is taken directly from Pete Ramey's book Care and Rehabilitation of the Equine Foot, Chapter 12: "Veterinary Management of the Laminitic Patient", written by Debra Ruffin Taylor DVM, MS, DACVIM
SID/SIRS Event Treatment:
Treat the primary disease process aggressively
Maintain the distal limb in ice water slurry continuously (for as long as 72hrs per session), during SID
Continue ice until 24hrs beyond resolution of all signs of SID or for 48hrs following treatment for acute grain overload
Change the diet of obese horses to a low glycemic index diet
Aggressively pursue an andocrine or metabolic etioligy for lean laminitic horses with no history of SID while instituting a high energy low glycemic index diet
Following the SID event (this also applies to hormonal laminitis), the main focus should be re-establishing perfusion (circulation) at the corium. In an acute sinker, the solar corium is being crushed and the lamellar corium is being stretched. When the solar corium is crushed, it has little blood flowing into and out of it, and with no circulation, no healing can occur and cell death could be the result. For comparison, when you press into the gums of the mouth, they turn white (lack of blood flow) and when you let go the blood rushes back and they return to pink. When the solar corium is being constantly crushed, the blood gets pushed out, and can't get back in. We need to relieve this and get the blood flowing back in. In order to fix this, follow proper trim protocol, and use soft padded boots, or soft padded casts (I've heard FormaHoof can accomplish this task as well, but I personally have no experience with it). Padded boots are usually the best option during the laminitic event, while the horse has issues lifting and holding up it's feet from the pain. With a proper trim relieving any mechanical separation, and soft padding allowing for the support of the coffin bone, we can achieve perfusion. The soft padding will allow for a release of this crushing, and the blood can flow in and out once again. With this type of laminitis, it is not recommended to exercise the horse beyond what it is willing to do on its own, such as walking in and out of the stall. Try to avoid hauling, the corium has been severely damaged and any added stress is to be avoided. Offer your horse deep bedding and an area they can walk in and out of the stall if they wish. Although this type of laminitis isn't hormonal in origin, it is still a good idea to overhaul the diet, limiting sugar and starch and balancing minerals and supplementing vitamins.
Hormonal laminitis is not caused by systemic inflammation. The main trigger is hyperinsulemia (high insulin levels) as seen in Insulin Resistance (IR), Equine Metabolic Syndrome (EMS), and Pituitary Pars Intermedia Dysfunction (PPID) with IR. To control this type of laminitis, we need to control insulin levels by keeping the diet intake total sugars at less than 10% ESC + Starch, and implementing exercise, we also need to trim to remove mechanical leverage and provide any hoof support we can. We do not want to lock up a horse in a stall if they're suffering from hormonal laminitis, they need to be able to move to help regulate their insulin levels. If it is an emergency, please follow the ECIR (Equine Cushings and Insulin Resistance) Groups's emergency diet, found at: https://www.ecirhorse.org/DDT+E-diet.php I also recommend joining their group if you have a horse that is having an emergency, they are incredibly knowledgeable and helpful folks.
The emergency #diet is basically my suggested feeding program, with the tweak of soaking hay for 1hr before feeding. Be sure to dump the (now filled with sugar) water away from the animals, so they can't drink it or get into it. This low sugar diet is CRUCIAL to controlling hormonal laminitis and is always my starting point for rehabilitation of laminitic horses because if hyperinsulemia is not addressed, we will never get control over the laminitis. Since there is no known systemic inflammation preceeding the hormonal acute laminitic event, NSAID's do not seem to relieve pain from the hooves. They will help with muscle pain from compensation, but if the cause is not from systemic inflammation, the NSAID will do little to nothing to help the horse in pain. The number one method is diet and controlling insulin levels. Your next step here, after getting the laminitis under control, would be to get a metabolic panel run on your horse to diagnose any underlying condition. It is recommended that (In the USA) you send your blood to Cornell University for testing, here is a link to their site where you can order tests and submit samples: https://www.vet.cornell.edu/animal-health-diagnostic-center/testing/protocols/equine-ppid
Here is a link to the ECIR site with instructions to give your vet on handling the samples: https://www.ecirhorse.org/DDT+E-diagnosis.php Remember, when testing:
Do not haul or do strenuous exercise for 24hrs before the test
Do NOT fast your horse. Make sure they have access to hay all night and the day of the test
Take the test in a quiet barn, where your horse is not stressed
We are trying to get a baseline of normal results and avoid getting false positives or false negatives, and following the above protocol should help. For example, if your horse has been on a long trailer haul, and/or is in a stressful barn situation, they will have elevated ACTH levels which may cause a false positive for the PPID test. If you fast your horse before the insulin test, the results may show a "normal" level of insulin. We want to get an idea of what the majority of life is like for your horse, how are they doing on a normal day, getting turned out and fed as regular as possible.
In treating hormonal laminitis, we also have to think about hoof circulation (perfusion) just as with SID laminitis. We may be dealing with lack of blood flow to just the periphery of p3, or the entire solar corium. Padded hoof boots, padded casts, and padded glue on shoes are all great options to help provide comfort and support to help with achieving perfusion. WIth radiographs, marking the hairline and dorsal wall down to point of breakover will help with prognosis as well as with indications of where to trim to relieve leverage.