South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
supplements (magnesium, chromium, vanadium, cinnamon, etc.) have been advocated to both
assist with laminitis recovery and enhance weight loss, data supporting use of these agents is
limited.
Carbohydrate content of forage: It is well recognized that “sweet feeds” and other concentrates
high in soluble carbohydrate (with a high glycemic index) are best avoided in obese, IR, laminitic
horses. Despite proliferation of “low starch” pelleted feeds, it is also important to recognize and
to recommend to clients that overweight horses do not need any concentrate feeds at all. In fact,
all essential nutrients and energy can often be found in good quality forage, although many
practitioners and nutritionists continue to recommend addition of a vitamin and mineral
supplement to a forage only diet (a ration balancer to complement a forage diet).
Lush grass pasture and some hays can also be a rich source of soluble carbohydrate. In fact,
grazing lush spring pasture can be similar in dietary intake of soluble carbohydrate to feeding a
high concentrate ration. Soluble carbohydrates are those that can be absorbed in the small
intestine and lead to increases in glucose and insulin concentrations. In contrast, insoluble
carbohydrates are contained in plant cell walls and require bacterial fermentation in the cecum
and large colon for digestion. The end products of fermentation are volatile fatty acids that are
absorbed in the large intestine and provide more than 50% of an equids daily energy needs.
Studies in which soluble carbohydrate content of pasture grass has been measured at various times
of the year have shown a spring rise, peaking in April through June depending on latitude. In
addition, there is a diurnal pattern to pasture soluble carbohydrate content. Specifically, during
daylight hours fructan content (fructan is one of the soluble carbohydrates in forage) increases.
During the night, plant cells utilize fructans as an energy source in the absence of photosynthesis
much as liver glycogen is utilized in mammals in the hours preceding meal ingestion.
Not surprisingly, serum insulin concentrations in equids grazing pasture at these various times of
the year have shown substantially greater increases when pasture soluble carbohydrate content is
high (spring and to a lesser extent in fall). Further, in ponies with historical pasture-associated
laminitis, a more dramatic increase in insulin concentration is observed after grazing, in
comparison to ponies that have never had laminitis.
Whether or not it is “safe” to allow overweight equids to graze pasture as a forage source remains
controversial. Pasture, especially lush spring and early summer pasture, should be considered
similar to feeding concentrates high in soluble carbohydrates and should be avoided. Further, if
pasture is to be utilized it may be preferable to turn equids out in the early morning hours while
plant fructan content is relatively low. On the flip side, being turned out to pasture has the benefit
of some exercise, as compared to being in a stall or small dirt lot. Grazing muzzles can be a good
compromise for turning overweight horses out on pasture.
Hay is usually cut once the forage plants have neared maturity; thus, hays typically have less
soluble carbohydrate content than pasture with grasses having less than legumes (alfalfa and
clover). However, various batches of hay cut from nearby fields may appear similar but can have
variation in soluble carbohydrate content depending on maturity, time of day that hay was cut
(often in the late afternoon to allow the dew to dry off – when fructan content may be highest), or
whether or not there may have been frost damage (fructan is not utilized when the plants are
frozen). Unfortunately, the only true way to assess forage soluble carbohydrate content is to have
the forage analyzed. This is not really important for horses that are in good weight and in a regular
exercise program but it is warranted when trying to identify a hay source for an overweight, IR,
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