One of the first things you are likely to be told, as the owner of a laminitic horse, is "no treats, no carrots, no apples..". A grape or prune is sometimes suggested as a suitable treat for hiding pergolide tablets, but owners are often warned not to use a slice of carrot or apple for the same purpose. So what's the science behind this?
We compared the analysis of carrots, apples, plums, grapes and prunes - all fruits/veg that might be given to a horse as a treat or to hide medication - on the SELF nutrition data website:
But how does the sugar/starch in carrots compare to other common feeds, such as hay?
A 500 kg horse eating 2% of its bodyweight would be having 10 kg dry weight, or approx. 11.2 kg as fed weight hay/day. Sticking to as fed figures, say the hay is 7.15% combined ESC (simple sugar) and starch (or 8% DM), that would be 800 g of sugar/starch eaten in a day. If eaten over say 16 hours (so 700 g hay as fed/hour), that would be 50 g of sugar/starch in each of those 16 hours.
So if 700 g of 7.15% sugar/starch hay as fed gives 50 g sugar/starch,
100 g hay as fed would give 7.1 g sugar/starch
and 100 g carrot as fed gives 6.1 g sugar/starch
- so a carrot doesn't look quite so evil now!
To be fair, that 100 g of hay has also provided a lot of fibre, some protein, fat, minerals and vitamins, whereas the carrot has mostly provided water, but also that valuable vitamin A.
And compare a carrot to say Spiller's High Fibre cubes which are approved by the Laminitis Trust (NB The Laminitis Trust Feed Approval Mark should not be taken as indicating that a feed is safe for laminitics - their criteria is that the NSC of the feed should not exceed 40%* - the ACVIM Consensus Statement on EMS suggests that NSC should not exceed 10% of the diet for horses with EMS**) - they contain 10% starch and 4.5% sugar***, so 100 g of High Fibre cubes would give 14.5 g sugar/starch - more than twice as much sugar/starch on an as fed basis as the same weight of carrots.
To help human diabetics, glycaemic index (GI) has been calculated for common foods. The glycaemic index ranks foods from 0 to 100 according to how much and how quickly blood sugar levels are raised after healthy humans have eaten a certain amount of the food (to provide a controlled amount of digestible carbohydrates). The University of Sydney gives 80 g raw diced carrots a GI of 35 (2017). The glycaemic load may be more helpful - this takes into account the effect on blood glucose from eating a typical portion. High water content foods like carrots usually have a low GL (less than 10 is considered low - 80 g raw diced carrots have a GL of 2 according to the University of Sydney (2017)). See Debunking the Carrot Myth - Glycemic Index Foundation. NB these figures relate to humans, not horses.
In her book "The Truth About Feeding Your Horse", equine nutritionist Clare Macleod busts the myth that carrots "should not be fed to .. those prone to laminitis" and agrees that although on a dry matter basis carrots are relatively high in sugar, on a fresh weight basis they are low in sugar (she suggests a fresh carrot contains around 7.5% sugar). She recommends feeding carrots for their betacarotene content (vitamin A precursor), particularly for older horses, to help provide antioxidants.
As always, common sense should prevail - if a horse's insulin is too high and/or it currently has active laminitis then hold back on the carrots and keep the diet as strict as possible, just analysed & soaked hay with appropriate levels of protein, minerals & vitamins, plus perhaps linseed to provide Omega 3 if a horse doesn't get grass. But once insulin levels and symptoms are under control, then a carrot or two a day, particularly if sliced and fed throughout the day rather than in one go, is unlikely to do any harm, and could do a fair bit of good.
For more information about feeding horses with laminitis, EMS and PPID, see The Laminitis Site's Diet page.
* Laminitis Trust Approval Mark for horse feeds
4. NSC (%) must not exceed 40% of the dry matter of the feed (where NSC is used as an estimate for the hydrolysable and rapidly fermentable carbohydrate feed fractions)."
** ACVIM Consensus Statement Equine Metabolic Syndrome (2010)
It is therefore recommended that NSC be calculated by adding starch and WSC percentages together, and this value should ideally fall below 10% of dry matter when feeding horses or ponies with EMS.
*** Spillers High Fibre Cubes nutritional analysis
Updated 2017 to include swede, turnip and parsnip (click on the image to enlarge it)