PPID is diagnosed in about 20% of horses over the age of 15 years. In over-30s, it affects as many as one in three horses. Even though we still don’t know exactly how PPID causes laminitis, it is the second most prevalent clinical sign. A 2018 study showed that almost 50% of PPID horses had laminitis . Only hypertrichosis scored higher at 70%. If your horse is 15 years old or older and develops laminitis without it being immediately clear what caused it, testing for PPID is always a wise choice.
When too much insulin circulates in the blood, we speak of hyperinsulinemia. Insulin resistance is the situation where cells do not respond properly to insulin. These two phenomena together are called insulin dysregulation (ID). Insulin dysregulation affects two out of every three horses with PPID (although some studies mention one in three). In comparison, just 3% of senior horses without PPID have elevated insulin levels.
25+ and healthy is not a guarantee
These figures are reassuring if you have a senior who does not have PPID or ID and is at a good body weight. Unfortunately, It’s not that simple. A Swiss study showed that laminitis in aged, healthy horses is not predicted by high BCS, CNS or elevated ACTH levels . The horses in this study, which were all over 15 years old, were healthy and showed no signs of lameness or other characteristics of laminitis. One striking finding as that coffin bone rotation was three times more likely to be found on X-rays in horses aged 25 and higher than in those aged 15 to 25. It makes little difference whether this is labeled as subclinical, low-grade, or plain laminitis. What is more crucial is that changes are occurring in the hoof that you can neither ascertain by your horse being tender footed, nor predicted by metabolic issues such as ID or PPID. In fact, no link was found between BCS, CNS or ACTH levels (an indicator of PPID) and an increased risk of laminitis in this study.
X-rays every year?
Sure, you could have x-rays taken of your horse’s hooves every year, but that is like carrying water to the sea and also costly. Optimising your elderly horse’s living conditions in terms of nutrition, housing, exercise, and hoof care makes more sense. This is of course important for all horses, but it might not yet have your full attention because your senior horse does not have PPID or insulin issues and has not been laminitic before. Make sure the latter stays that way. It may well be that your horse has already had a few episodes of subclinical or low-grade laminitis (read: Subclinical and low-grade laminitis). According to some researchers, this increases the likelihood of developing clinical laminitis. You may not even have noticed that your horse was actually laminitic. Obviously, in an older horse, the chances of these two scenarios are statistically higher.
Another explanation could be that PPID was already developing in the older horses, without a link to ACTH levels having been identified. This is referred to as subclinical PPID. It emphasises the need of understanding how PPID causes laminitis.
Advanced age = higher risk
As is quite often the case, this study leaves room for some doubt. For instance, shod horses were mixed up with barefoot horses, as were different breeds, and the study population was on the small side. It was also not determined whether the horses in the study had insulin dysregulation. On the principle of ’no harm, no foul’, it appears prudent to regard advanced age as a risk indicator, even if other risks are absent or unknown.