It is tempting to allow horses unlimited access to pastures as soon as the grass turns green, particularly after a long winter. Yet mindful management of this transition is crucial to the well-being of the horse.
In natural rangeland conditions, new spring grasses are covered with a dry forage mat from the past growing season. Horses grazing under these conditions go through a slow and steady natural transition, ingesting a mix of old-stand forage and new-growth grasses, gradually consuming more and more fresh forages.
Since horses are very sensitive to diet changes, especially when the change occurs to a much richer feedstuff, this four- to six-week seasonal transition is very beneficial. By gradually introducing spring grass, the population of microbes responsible for digestion of plant matter in the hindgut have the ability to adjust.
When large quantities of fresh spring grass are consumed, especially if introduced suddenly, the change in diet can play havoc with both the digestive and metabolic systems. This can range from mild loosening of the stool and/or diarrhea, through to painful colic due to stretching of the intestinal wall from the buildup of gaseous byproducts of fermentation.
Some individuals are particularly sensitive to the metabolic consequences of elevated blood glucose and insulin levels following consumption of high levels of soluble carbohydrates (that is, sugars and starches). Often described as ‘thrifty’ or ‘easy-keeping’ these individuals tend to seamlessly gain weight, often trending quickly towards obesity. When forage is scarce and of poor quality this sensitivity has a survival advantage but becomes problematic. Horses have not evolved to handle the continuous elevation of blood glucose levels from rich diets (really, no species has).
Elevated blood glucose levels trigger a spike in the insulin hormone. When this elevated combination exists in a chronic state, beneficial feedback loops within the horse’s body fatigue and biochemical pathways fracture. This then exposes all tissues of the body to metabolic injury and harm over time.
Researchers and clinical experience have shown the fragile metabolic tissues within the hoof capsule to be at particular risk. Recent findings suggest that up to 90 per cent of all cases of ‘modern-day’ laminitis in horses, ponies, donkeys and/or mules and minis can be attributed to their insulin sensitivity and the dysregulation associated with the consumption of high dietary sugars and starches (which trigger insulin release).
An unexpected, first-time episode of laminitis in the spring and/or fall can be a red flag to identify these sensitive individuals.
Even though all equines are vulnerable to chronically elevated levels of blood glucose and insulin, horse breeds such as Canadian Morgans, Andalusians, quarter-horses, Icelandics, Fjords, and ponies are likely the canaries in the coal mine as they clinically express their metabolic incompatibilities with a greater frequency.
These diabetic-like illnesses are labeled as pattern-specific obesity, insulin dysregulation, equine metabolic syndrome and Cushing’s syndrome or PPID (pituitary pars intermedia dysfunction). Physically they initially present with an ‘abnormal’ pattern of obesity with isolated fat deposits along the crest of the neck (the cresty neck), above the eyes, along the abdomen and over the tail-head. They are particularly susceptible to a laminitic event or the painful inflammation within the hoof also known as founder.
The unsupervised grazing of lush spring pastures in this group of horses rapidly leads to obesity and can trigger a cascade of events culminating in laminitis and/or founder. Vigilant management of these sensitive horses and ponies will continue to be necessary beyond springtime.
Currently ‘super-grasses’ dominate the modern-day forage landscape in pastures, rangelands and hay lands. They have been genetically selected for their ability to increase cattle gain performance such as weight gain and milk production. Unfortunately, these high-octane forages are less suited for sound long-term equine nutrition as the concentrated sources of easily digestible carbohydrates in these forages can quickly overwhelm the equine metabolic system.
The detrimental metabolic consequences are amplified if the horse leads to a sedentary lifestyle. Exercise and/or movement have a protective effect upon elevated levels of blood glucose and insulin sensitivity mitigating the biological injury incurred by the horse.
Therefore, successful management requires a level of awareness by the owners.
Since lush spring growth is particularly problematic, it is a good strategy to wait until the grass in the pastures reach six to eight inches in height and then gradually introduce grazing times dependent upon the individual horse’s sensitivity.
A good practice is to feed horses their normal hay diet before turning them onto pasture during the first several grazing days to slow down their consumption of the pasture grasses. It may be advisable to limit grazing to the early-morning hours when pasture sugars typically tend to be at their lowest levels.
Prudent management practices of horses ‘as if’ they are sensitive to ongoing dietary intake of high levels of sugar and starches will generally improve health and, for the particularly susceptible horse or pony, it becomes essential to ensure their health and longevity.