There are significant Differences Between Feeding Horses on Warm Season vs Cool Season Grasses
Ten days in Queensland, Australia where the climate is sub-tropical, highlighted the differences between feeding horses grazing Warm Season vs Cool Season grasses.
Significantly horses grazing Warm Season grasses are more likely to be affected by DEFICIENCIES compared to Cool Season grasses of temperate climates of the southern half of Australia, NZ and other parts of the world where the horse’s metabolism is more often negatively affected by EXCESSES.
Deficiencies are much simpler to address because it works to add nutrients into the diet. Dealing with excesses is not so easy because you can’t take the offending excesses of for example, nitrogen and potassium, out of the grass.
Whoever gives you nutritional advice for your horse needs to understand these differences. What we observe from assisting horse owners to resolve issues is that this is not necessarily the case – dietary recommendations for horses living on Warm Season grasses tend to be the same as for horses grazing Cool Season grasses.
Cool-season grasses (C3) evolved to photosynthesize more efficiently in cooler, temperate environments. Such grass greens up faster in the spring and stays green longer into autumn.
When summers are hot and dry, these types of grasses go dormant until it rains again.
Lucerne (alfalfa) is a Cool Season Legume with a faster photosynthesis rate than grasses resulting in a high leaf protein content. Adding this to an already too high Crude Protein content of Cool Season grasses, in our experience causes a great many serious issues from digestive issues (loud, gut noises, diarrhea), laminitis, HS, anxiety, being spooky, explosive, sacro-iliac issues and so on .
Cool Season grasses are more nutritious than Warm Season grasses, having higher levels of protein, non-structural carbohydrates, fructans and water. They are lower in fibre so it is vital to supplement grass intake with plenty of plain grass hay. Thinking green grass provides enough fibre is a major contributor to the development of ulcers and other digestive issues.
Cool Season grasses also have a higher chlorophyll content hence they look darker green than warm season grasses - this translates to a higher Non-Protein Nitrogen component which the horse's metabolism is not adapted to.
One advantage of Warm Season grasses is that they are much higher in fibre than Cool Season grasses (as much as 36% higher).
However, horses grazing them are very prone to DEFICIENCIES which result in ill-thrift (lack of quality protein and lack of vital minerals like salt and calcium) and metabolic problems such as Anhidrosis (inability to sweat) which resolves with proper supplementation (see pics).
Another of the major deficiencies is caused by OXALATES in Warm Season grasses - oxalates bind calcium making it unavailable to the horse. The oxalate content of grass varies with the species and growing conditions. Oxalates are highest when the grass is in the vegetative (growing) phase and lower in more mature plants.
Horses grazing oxalate grasses (eg kikuyu/setaria/buffel/green panic) or consuming Teff hay therefore need to be supplemented with properly formulated multi Vitamin/Mineral/Calcium supplement (Supreme MVA with XtraCal) to avoid disturbances to calcium metabolism which can cause all sorts of metabolic, lameness and skeletal issues including Big-Head (see photo).
Horses grazing Cool Season grasses – (the majority of horses in Tasmania/Victoria ie the southern half of Australia, NZ, UK) suffer the effects of EXCESSES. These horses are easier to keep in good condition and shiny, but the equine metabolism can lose its ability to cope with the chronic EXCESSES of Crude Protein (especially the NITRATES), Potassium and the sugars/fructans.
Warm-season C4 grasses thrive in warm weather (30 degrees C plus), more tropical climates and use a slightly different process to photosynthesise and produce their energy. Warm season grasses can thrive on less water and while being lower in protein, are higher in starch than Cool Season plants.
Horses grazing both types of grasses require salt added to their feeds.
Both types of grasses need management to ensure the stage of growth at which grazing access is suitable for horses and while horses do best on grassy hay, many horses on Warm Season grasses tolerate and thrive on a grassy/lucerne hay mix or with up to 10% of their forage as lucerne (avoid Prime Lucerne).
Both types of grasses can equally cause laminitis but while Head-Shaking does occur in horses in QLD on warm season grasses, significantly the incidence of HS is much higher on the Cool Season grasses of Victoria and Tasmania, NZ & UK.
Big-Head - the horse (below) was living on Setaria with no feeds/supplements - on enquiry a couple of years later, sadly, he had been euthanised.
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