Senior Science
Feeding and managing horses well into their twilight years requires a balance of art and science. Together with our collaborators around the world, we have been involved in senior horse research for over twenty years as part of our ongoing commitment to helping older horses and ponies live happier, healthier lives.
Our journey began in the early 2000s with research into the flavour preferences of stabled horses and has since extended into various areas including nutrient digestibility, protein requirements, insulin response, gut microflora, travelling stress and PPID. Here we share a few highlights from some of our more recent studies. Of course, there have been others and there will be more to come, so look out for the latest senior science news here.
Nutrient digestibility
Several of our studies have shown that in healthy horses fed appropriate amounts of forage, simply ‘being senior’ doesn’t affect protein, fibre or mineral digestibility, regardless of the type of diet fed (hay plus a fibre and oil rich feed or hay plus a starch and sugar rich feed). However, providing suitable amounts of quality protein, vitamins and minerals is still very important and is unlikely to be achieved by feeding forage alone.

Pituitary pars intermedia dysfunction (PPID: also known as Cushing’s syndrome)
Research we published in 2018 found that a high starch diet may increase the concentration of adrenocorticotropin hormone or ‘ACTH’ in blood, potentially leading to the misdiagnosis of PPID. Some of our most recent studies are helping to improve our understanding of several hormones involved in PPID including most importantly ACTH and dopamine, as well as their interactions with insulin. The aim being to improve our ability to diagnose and manage horses and ponies with this condition.

Travelling stress
Even short journeys in horses that are used to travelling can lead to stress and while you may not notice any changes in your horse’s behaviour, this may have an effect on their immune system or metabolism. Our research found travelling can increase concentrations of insulin and ACTH in the blood, especially in senior horses, which may potentially lead to a misdiagnosis of insulin dysregulation or PPID.

Starch & sugar
While not all horses and ponies with PPID are insulin dysregulated, many of them are which means they are at an increased risk of laminitis. However, two of our studies found even healthy senior horses can have an increased insulin response to a meal high in sugar and especially starch. This suggests that restricting starch and sugar intake may be beneficial for all seniors, regardless of whether they have PPID or a history of laminitis.

Marvels of the microbiome
The horse’s large intestine or ‘hindgut’ is home to trillions of tiny microbes including bacteria, viruses and fungi which are essential for fibre digestion and helping to regulate the immune system. Our research found that age is associated with a less diverse population of microbes in the large intestine in horses (but not in similarly aged ponies) which may make them more sensitive to changes in diet. The fact the same reduction in diversity was not seen in ponies may be a sign that they ‘age later’ than horses.

Muscle scoring
Muscle wastage can affect health and welfare in a number of ways, including a reduced ability to work or even simply getting up after laying down. In 2022 we helped to develop a system for scoring muscle wastage in the neck, back and hindquarters. This system may be particularly valuable in senior horses and ponies and importantly, includes two scales which are based on the body condition of the horse – did you know horses of all ages can have a high level of body fat but low muscle mass or vice versa?!
Reasons for retirement
By developing a better understanding of when and why senior horses are being retired, we hope to help owners and vets to be better placed to monitor for, prevent (where possible), and treat the underlying conditions early on. Our recent survey completed by >2700 owners/ carers of senior horses (15 years and over) in the US found:
Most horses (62%) were retired between 15-24 years of age, with health problems given as the main reasons.
Horses with owner reported veterinary-diagnosed laminitis, lameness and degenerative suspensory ligament desmitis had higher odds of retirement than those that did not have these conditions.
Around 1 in 6 horses had low muscle mass (muscle wastage) according to their owners and in most cases, owners felt this affected their horse’s welfare and ability to work.
Age, sex, osteoarthritis, laminitis, PPID, and primary use were identified as risk factors for low muscle mass.
Retired horses were at higher risk of low muscle mass than horses used for competition or pleasure riding.

Health of the senior population
In follow-up to the retirement study, we published further data regarding the health and care status of senior horses in the US. Only 36% of owners/ carers reported their horse/ pony to be free from veterinary diagnosed illness, with osteoarthritis (30%), dental issues (15%), lameness (14%) and PPID (12%) being the most commonly owner reported veterinary diagnosed health issues. In this study, the risk of no health care visits, no dental visits and being visited by the farrier <4 times per year was found to be around 2 times higher in retired senior horses vs seniors used for pleasure riding.