As humans are living longer our beloved equines are too. What is considered an older or senior horse? We find that a commonly acknowledged description of an aged horse appears to be 20 years of age or older. However, it must also be acknowledged that there are differences between individuals in terms of those exhibiting geriatric signs at earlier stages than others, there are many very healthy older horses with few specific health or nutritional considerations. This can often reflect the younger life of the horse, whether they were involved in high level performance or if they were at ‘rest’. Feeding, exercise and general management regimes may then differ for these categories. There is limited data regarding specific physiological differences between aged and younger horses, however, gross changes associated with ageing in humans are often found in the horse. For example, deteriorating dentition, degenerative disease, alterations in the digestive and immune systems are some of the time-related changes aged horses have to cope with.
While preparing this article I spoke to some experts in the area of retraining and rehoming retired performance horses and the feedback I received from them was that the more common issues with older horses in their care revolve around digestive issues, dentition problems, hoof care, body condition, joint mobility and coat health. Skilled professionals in this field take a very holistic approach in terms of overcoming these challenges and find that with the correct care and diet they can get these horses back to a very healthy status enabling them to have an excellent quality of life. Other cases can be more difficult to manage depending on the specific challenges those individuals are facing as they grow older.
A useful place to start with is often the gut itself. Parasitic burden can be an issue and a good worming programme specific to the age of your horse should be devised with Veterinary advice. Due to various feed types and management regimes, horses fed inadequate amounts of good quality roughage and potentially higher quantities of starchy feeds can commonly suffer from acidosis of the hindgut which is essentially a reduction in the pH environment and an alteration of the microbial population within the caecum. Increased access to roughage, inclusion of a live-yeast or probiotic in the diet can help restore the gut to a healthy pH and help replenish the billions of microbes living and working within the hindgut.
Dentition, or rather failing dentition, is a common occurrence in older horses. Horses’ teeth wear at the rate of around 2-3mm per year until about 20 years of age when shedding of the teeth begin. Effective digestion and fermentation of forage is dependent on effective grinding or mastication by the molars or cheek teeth. Over time, abrasive surfaces become worn, and diastemas arise between teeth leading to gingivitis and food pocketing. Loss of condition, quidding and choke can often indicate dental issues. As the animal becomes less able to cope with forage (especially long fibre) a higher proportion of the diet tends to come from concentrate sources resulting in reduced mastication and the lateral excursion (side-ways movement) that would naturally aid in minimising the formation of sharp edges. This can lead to conditions, such as ‘step’ and/or ‘wave’ mouth of which there is a high prevalence in aged horses. Routine and regular check-ups with a qualified equine dentist will go a long way to minimising the age-related effects on dentition.
Aside from the physical aspects of deteriorating dentition, there is the potential reduction in nutrient digestion and absorption. It appears that aged horses exhibit significantly reduced digestibility of both crude protein (CP) and phosphorous (P), as well as a tendency for reduced fibre digestion.
Glycaemic and insulinaemic responses in horses have received much attention in recent years and insulin sensitivity has been theoretically linked to increases in the risk of certain conditions, such as laminitis. Again, the comparison of responses in young vs. older horses is limited. However, preliminary indications seem to demonstrate much higher peak insulin concentrations in mature vs. younger horses, despite the young animals having higher peak glucose concentrations, indicating a reduced insulin sensitivity in the mature animals.
Osteoarthritis (OA) and reduced locomotory ability is common in the aged horse. Osteoarthritis is a progressive, degenerative disease of the joints characterised by gradual loss of articular hyaline cartilage resulting in bone spur formation and fluid-filled joints. It is not simply a condition of domestic horses and has been found in wild ponies as a natural, age-related process. Many oral supplements are commercially available claiming to reduce the negative effects of degenerative joint problems. The majority of them focus on the perceived benefits of glucosamine and / or chondroitin.
Antioxidant status can be viewed as the balance between anti-oxidative and pro-oxidative compounds. The pro-oxidative reactive oxygen species (ROS) have been implicated in the ageing process in animals as the balance between antioxidants and pro-oxidants tips towards the latter and tissue destruction occurs. The major antioxidant compounds are selenium and vitamins E and C. Vitamin C is synthesised within the body of the horse, however, may be compromised by issues, such as pituitary tumours. Equine Cushings Disease is more accurately known as Pituitary Pars Intermediary Dysfunction or PPID. It is exhibited by a number of signs including hair coat changes, muscle and weight loss, laminitis and others due to overproduction of certain pituitary hormones. Horses with Cushings tend to have lower plasma ascorbate levels. Definitive effects of age on antioxidant status have yet to be defined.
Effects on the immune system and inflammatory ageing have also been discussed in both humans and horses. Despite limited data in horses, the major alterations appear to involve a shift in T cell population from naïve to memory T cells. There is an overall reduction in T cell proliferation and horses appear to exhibit similar inflammatory ageing characteristics to humans and mice. However, separate responses can be seen with old, healthy animals vs. old, undernourished animals. Additionally, inadequate selenium status has been implicated in poor responses to vaccinations in aged horses.
It is apparent that there is limited data on most of the issues described above and further research is warranted as the active, aged horse population grows. If you have an older horse that you need assistance with it is wise to speak to your vet and reach out to your feed advisor or nutritionist.
If you have any queries relation to the nutritional requirements of your older horse, please get in touch with Joanne.
Joanne Hurley is a nutrition specialist with GAIN Equine Nutrition. She holds a Masters in Animal Nutrition and Production from UCD. Joanne can be contacted by email at firstname.lastname@example.org