Regional challenges in feeding

With regions ranging from cool temperate, temperate, arid, subtropical and tropical, the Australian climate poses some interesting feeding challenges, writes LARISSA BILSTON  

Australian horse owners face very different management challenges depending on the climatic zone they live in. The impact of climate on pastures, feed quality and availability across different regions has a significant influence on what you need to feed your horse to optimise health and nutrition. 

High oxalate pastures – tropical climates and coastal areas Graziers introduced many species of high-producing C4 grasses from Africa into tropical Australia in the last century. Many of these grasses were very successful in Australian climates and have now become naturalised throughout tropical and sub-tropical zones. Some C4 species also grow alongside naturalised C3 grasses in temperate zones.  

Most of the introduced C4 pasture grasses contain high levels of oxalates, which are a naturally occurring biomineral that help plants to regulate calcium levels and photosynthesize efficiently. Many plants contain oxalates but only some contain the very high levels that can cause problems for horses 

Species of high oxalate grasses that most commonly occur in horse paddocks in the northern half of Australia are Buffel, Setaria, Green Panic, Humidicola, Para, Signal and Pangola grasses. Kikuyu is another high oxalate species which grows well in coastal areas from northern Australia right down the eastern coast and into north-eastern Tasmania. 

The problem with these grasses in horse pastures is that the oxalate molecule binds calcium, making it unavailable to the horse. Interestingly, oxalates do not cause problems for sheep and cattle because their rumen (the first stomach of a ruminant) can metabolize oxalates into harmless products very early in the digestive tract.  

If not supplemented with adequate calcium, horses grazing high oxalate pastures become calcium deficient and draw on the calcium reserves in their bones to maintain critical blood calcium blood levels. This condition is called Big Head/Bran Disease, more accurately known as nutritional secondary hyperparathyroidism (NSH) which is effectively osteoporosis in horses.   

Horses grazing high oxalate pastures need to be supplemented with extra calcium to ensure there is enough available calcium in their diet to meet their requirements. Both inorganic and organic (chelated) forms of calcium are effective provided that they are supplemented in adequate amounts. Since there are many variables to be considered in calculating supplementation needs, advice from a qualified nutritionist experienced in tropical equine nutrition is recommended. 

Sweet grasses and laminitis prone/insulin resistant horses: Many of the high producing C3 grasses introduced last century from Europe, the UK and USA for temperate sheep and cattle production have succeeded so well in the Australian climate that they are now naturalised species. These grass species have been bred to produce rapid growth of the high energy (calorie), high protein feed needed for milk and meat production. 

The carbohydrate (sugar and starch) levels of ryegrass and some other introduced grasses, particularly the C3 species, are too high for horses who evolved to graze lower quality roughages. Horses rapidly gain weight on high carbohydrate pastures which puts them at risk of equine metabolic disease, insulin resistance and laminitis. Sudden changes in grass quality and availability especially during spring and autumn can disrupt the equine gut microbiome which causes diarrhea and may lead to colic and laminitis. 

When planting horse friendly pastures in temperate zones choose a mix of slower growing, higher fibre, lower nutrient varieties such as Cocksfoot, Browntop Bentgrass, Yorkshire Fog, Crested Dogtail Grass Prairie, and Australian native grasses – Wallaby, Native Wheatgrass, Native Bluegrass and Weeping Grass are amongst the best suited to grazing.  

Species for horse friendly pastures in tropical areas include Rhodes Grass (this is a high producing, low oxalate C4 grass) and native grasses such as Bluegrass, Native Wheatgrass, Mitchell, Kangaroo and Wallaby Grass. 

Horses prone to laminitis will need very careful management especially during spring and autumn. Restricted intake via use of grazing muzzles and removal from grass with or without limited turnout time are necessary management tools. Replace fresh grass with low calorie hay (which may be soaked to remove calories), and minimise hard feeds to just enough to provide essential vitamins, minerals and the prebiotics designed to improve insulin sensitivity. Consider the use of hindgut buffers and probiotic live yeast to help maintain a more stable hind gut pH. 

Lack of pasture: Most parts of Australia experience seasons where grass availability is inadequate to meet horse requirements. Grass growth can be limited by cold weather, short days, dry conditions and over-grazing. 

Whenever pasture levels are low or grasses are dry and stalky, horses need to be fed hay. Horses need a minimum of one per cent of their body weight as dietary forage. For the majority of horses, the required amount of hay is closer to two per cent of their body weight (i.e. a 500 kg horse needs 10 to 12kg of hay per day when grass is not available, and a 250kg pony needs 5 to 6 kg). 

The hay used to replace pasture intake should be a grass or meadow hay. Lucerne should not exceed more than 20 to 30 per cent of forage intake. 

Horses reliant on hay or dry pasture for more than half of their forage intake should also be given additional vitamins and an omega-3 fatty acid supplement to replace those levels lost from fresh pasture. Appropriate omega-3 supplements include DHA/EPA algal meal, fish oil, freshly ground or whole linseeds, stabilized linseed oil or chia seeds. 

Mycotoxins: Mycotoxins are the naturally occurring toxins produced by certain moulds. Their ingestion is a common cause of horse health and behaviour problems during wet weather and when endophyte (fungi and bacteria) containing varieties of fescue and ryegrass are present. Paspalum is also a high-risk species for mycotoxins during flowering. Many horse pastures will contain levels of myctoxins which are not detectable by the human senses, but are high enough to impact on horse health. 

Use of a good quality, broad-spectrum toxin binder containing multiple binding agents is recommended during high humidity or whenever horses show signs of being mycotoxin affected, such as loss of appetite, poor performance, colic and immune-suppression. 

Coping with hot summers: Minimising the risk of dehydration and heat stress is a major concern during periods of hot weather. Keeping and riding horses through an Australian summer requires an understanding of how to minimise heat stress and manage electrolyte balance. Working horses during very hot and/or humid weather can be potentially dangerous (even fatal) for both horse and rider. Horses rely heavily on their ability to sweat to cool their bodies during exercise. Sweating is only effective when humidity is low and a breeze is present. Hot, humid and still conditions make it much harder for the body’s core temperature to cool back down to a safe level. 

Strenuous exercise and hot environmental conditions are two major factors causing oxidative stress. Oxidative stress occurs when free radicals (reactive oxygen species) outnumber the antioxidant levels in the body, causing cellular and muscle damage, fatigue and decreased performance. 

Supplementing with additional antioxidants such as organic selenium, organic chromium, vitamins C and E, carotenoids and enzymes such as superoxide dismutase (SOD) during very hot weather or heavy exercise is scientifically proven to reduce the risk of oxidative stress. 

Daily salt requirements: Horses require between seven and 12 grams of plain salt per 100 kilograms of bodyweight every day. This is the amount required for maintenance. Even more is needed for sweat replacement on very hot days and following heavy exercise. 

Since salt is usually added to pellets and grain mixes designed for horses, these amounts must be counted in calculations of how much extra salt to add. Top up with plain salt (sodium chloride) which can be purchased as table salt, pool salt, flossy salt or stock salt. Free access to a container of clean, loose salt rather than a salt block is also advisable because many horses will not lick a block for long enough to meet their salt requirements. 

Sweat replacement: Sweating horses can lose as much as 10 to 15 litres of fluid per hour. Dehydration occurs if this liquid is not replaced. However, it is not as simple as just adding water.  

The fluid in animal’s bodies contains various salts called electrolytes (sodium, chloride, potassium, calcium) which help manage the hydration of individual cells and blood volume. The water and electrolytes lost in sweat will be gradually replaced over the course of a few days rest as the horse drinks water and eats a diet with the correct mineral balance.  

However, a faster recovery is often desirable for horses who work every day, or are living in hot and humid environments, or are competing over a number of days. These horses will benefit from a well formulated commercial electrolyte supplement. It is important to feed just the right amount of electrolytes because giving too much or too little can actually increase dehydration.  

Always make fresh clean water available to a horse after sweating. Do not offer electrolyte-enhanced water without providing access to plain water. 

Mineral supplements: Many horse owners recognise that horses grazing poor quality pasture, or who are on poor soils, need supplementation. But what is not well understood is that even the best quality pasture it’s possible to grow does not give a horse the ideal balance of minerals. Mineral supplements are needed no matter where you are in the world! 

What’s the difference between C3 and C4 plants?: It’s all about the way they photosynthesize – that’s the way they use energy from sunlight to convert carbon dioxide and water into energy for plant growth. The vast majority of plants use C3 photosynthesis.  

  • C3 plants store their energy as sugar (fructan) 
  • C4 plants store starch rather than sugar 
  • C4 plants are higher in fibre
  • C4 plants are more energy efficient and grow much faster 
  • C4 plants have a higher water use efficiency
  • C3 plants perform best in cooler, moist conditions with moderate sunlight and tend to be temperate plants (ryegrass, clover, wheat, barley, oats)
  • C4 plants evolved in the warm, strong sunlight areas of the tropics (sugarcane, corn, sorghum, Rhodes grass)

Larissa Bilston, BAgrSc (Hons 1), Nutritionist, Farmalogic. 

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