As we all know, feedstuffs high in starch, sugar or NSC should not be fed to insulin-resistant or at-risk horses……………and those high in fructans should be avoided in horses prone to laminitis. Today, with laminitis season at hand, and in areas where the drought has eased, lots of rain and pasture growth, we’re going to explore all the confusing terms and some of the equine clinical nutrition importance of carbs.

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Carbs is the common word for ‘carbohydrates’. And by definition, the meaning of the word ‘carbohydrates’ is plant sugar. Also found in milk, carbs are combinations of carbon, oxygen and nitrogen. Plants produce them through photosynthesis.

And, like us, plants store carbs for leaner times – we store carbs as fat…..plants store carbs as starch or fructans. Cold season grasses store their excess carbs in their stems as fructans, and warm season (C4) grasses store them in the leaves, as starch.

Compared to those used for energy, different carbs are used to build plant structures– never-the-less they are all still ‘carbs’ because they are produced during photosynthesis and are all made of carbon, oxygen and nitrogen. Carbs not used by the plant for structures (such as roots, stems etc) are differentiated from those that are - and called non-structural carbohydrates, or NSC.

NSC are the carbs used for energy and include sugars, starch and fructans.

So NSC = sugar + starch + fructans. When labs measure the amount of carbs in plants, they have to dissolve them to extract them from the grass. If they dissolve in water, they are called ‘water-soluble carbohydrates’, or WSC. Starch is not soluble in water, so WSC = sugar + fructans and ethanol-soluble carbs (ESC) is just the sugar part.

There are some published figures for different feeds e.g. beet pulp - NSC ranges from 7-17%. Some batches may be too high for some horses but soaking twice can reduce the NSC and beet pulp can replace around 40% of the hay in the diet. Half a kilo of dry beet pulp is roughly equivalent nutritionally to around a kilo of hay. Copra 6.6 – 14.7% NSC; ground flax 3.9-5.7% or small amounts of soy meal 12.3-18%, brewers/distiller’s grain 7.4-15.1%, or rice bran 16-34% are also suitable. Prepared commercial feeds containing corn 69-77%, oats 41-68%, wheat 51-69% or their by-products (bran 23-39%, pollard 35-40%, millrun 41-89%, hominy meal 30-465) are all high in NSC and should be avoided or used only with great caution.

When and if to let at-risk horses and ponies graze pastures must also be considered carefully. Following are a few facts and bits of research data that may be helpful when contemplating whether to let horses and ponies graze.

Grass NSC levels are the classic ‘supply-and-demand’ situation, so when growth (ie uses up sugar) is faster than photosynthesis (produces sugar), NSC levels will be lower eg shaded areas, cloudy days and in the early mornings from 3-10am. When shaded for 48 hours, carbs in Phalaris dropped from 126g/kg to 62g/kg. When there is lots of sun for photosynthesis, the supply of sugar can exceed how quickly the plant uses it up for growth. If water, fertiliser or cold weather limit growth, carb levels can get very high – even though the grass may not look green and rich. If night temperatures are below 5C, growth slows and NSC levels remain high. For Pangola grass, NSC can fall by 78% on warm night and only 2% on cooler 10C nights and horses are at higher risk when temperatures fluctuate below 5C for temperate C3 grasses and below 15C for C4 grasses. To help the decision re grazing, check out what sort of grass is in your paddocks at different times of year. And don’t forget weeds. Dandelions can have 27%, sweet clover 14% and wild oats 26% NSC.

So, although we may think dead grass and weeds are safe, they can have high levels of NSC……….and lush, rapidly growing grass is often lower carb because all the sugars are being used up for growth and there is little leftover for storage as fructans or starch. Also, remember that drought-stressed plants can be really high in NSC and also that it depends on whether the drought came on suddenly or developed slowly. In Setaria during a long term, gradual drought NSC doubled to almost 50%. For Cocksfoot and Ryegrass subjected to 45 days of drought, the NSC content rose steadily to over 40 %. The story is pretty much the same for hay because it doesn’t lose NSC during storage, so time of cutting and wilting are important – generally soft-leafy hay is lower in NSC unless cut when stressed by drought or cold weather

Avoiding lush green grass is not a reliable rule-of-thumb. Certainly, there are times when lush grass is high in carbs (temperature stress or at the heading stage) and should be of concern to caretakers of sugar intolerant equines. The bottom line is wherever possible have the NSC tested or ask the produce store/supplier to provide you with an analysis. Good luck and because nutrition is so closely involved in the cause, prevention, treatment and management of many equine veterinary clinical conditions, here at Jenquine we’re always happy to help.

Dr Jennifer Stewart