Summer feeding strategies
Article from RD1's 'Straight from the Horse's Mouth', December 2010.
Written by Dr J H Stewart BVSc BSc PhD MRCVS Dip BEP AAIM, Equine Veterinarian and Consulting Nutritionist.
About 75-80% of energy used in the body is given off as heat and this increases up to 60 times during hard exercise. The greater the heat produced, the more blood is shunted to the skin. This contributes to fatigue as it decreases blood supply to the muscle. Additionally, the gut flora - those beneficial bacteria, yeasts and protozoa that help digestion - are killed off en masse by high body temperatures. When this happens, the horse becomes lethargic, goes off its feed and manure may be loose.
The amount of heat produced and the rate of heat loss depends on dietary management, fitness, muscle mass and the ratio of body mass to skin surface area. Horses have a low ratio of surface area to body weight - a 60kg human has a skin surface area of around 1.7 square metres, whereas a 500kg horse has a skin surface area of only 5 square metres. So even though the horses body weight is approximately 8.5 times that of man, the skin surface area is only three times as large, and this places a limit on sweating. Bigger, heavier horses have a larger body mass to surface area than leaner horses, and this favours heat retention.
Signs of a critically high body temperature after work include agitation, inability to stand still and constant tail swishing. Rectal temperature, pulse rate, respiration and dehydration should be monitored when working horses in hot weather. Heart rate should drop to 40-50 beats per minute within 15 minutes of finishing work. In hot or dehydrated horses, the post-exercise heart rate recovery is slower, but respiration rate and rectal temperature will give you a better indication of heat stress.
Normal respiration rate is 10-20 breaths per minute. During the first 10 minutes after work, respiration rate may remain at 60-80 breaths per minute. Horses that are overheated may have rates of 120-140 breaths per minute because they are using the respiratory system to lose heat. Increased respiration rate may also indicate a bleeding episode has occurred and the trainer will need to decide if a veterinary examination is indicated.
Episodes of bleeding are more frequent in summer and the incidence is similar in standardbreds and thoroughbreds - around 75%. A study presented at the International Conference on Equine Exercise Physiology (2002) reported that whilst endoscopic examination found an incidence of 75%, if broncho-alveolar lavage (BAL) is used, the incidence is closer to 100%. Increased risk of bleeding has been associated with poor stable air quality and the incidence is reduced in dust-free stables. Other causes of bleeding include stress failure of the lung blood vessels, increased blood pressure and the flexibility and suppleness of the red blood cells.
Because the lungs are a major contributor to heat dissipation, all efforts should be made to protect lung health and prevent respiratory disease. The stress on the respiratory system increases in hot weather, which may in part explain summer rise in bleeding. Hay, raw grains and bedding are the major sources of stable air contaminants, in terms of respirable particles, fungal spores and bacterial fragments. Human grain workers develop inflammatory airway disease in response to dust and particles in the raw grains. A similar condition has been found in stabled horses and is thought to be more significant than the 'virus' as a cause of respiratory disease.
Soaking hay for six hours to reduce particles and dust and the use of steam-extruded grains, which are low in dust and moisture, are major steps that will improve air quality and hygiene. MitaviteŽ has steam-extruded barley, corn and lupins -providing safer, cleaner, low allergenic feeds. Increased digestibility of steam-extruded grains also reduces the weight of feed required and waste heat production during digestion. Red cell strength and flexibility is improved when Omega 3 supplements are included in the diet. Mitavite Performa 3 oil has 10 times as much active form of Omega 3, than other oils, meaning less is required to achieve results.
Added to this in summer, are the combined increases in energy requirements and the increased demand for cooling. Energy requirements are 14-27% higher in hot weather. The heat-stressed horse decreases feed intake and this, combined with the increased energy requirements, result in weight loss. Energy requirements double in heavy training. Traditionally, this increased energy requirement was met by increasing grain intake, but this increases the risk of gut upsets from fermentation and a greater risk of tying up, colic and laminitis. Subclinical laminitis is a major cause of poor performance, but because it usually only causes pain at full racing speeds, it is difficult to diagnose.
Oil is an excellent source of energy, providing 2.5 times as much energy as an equivalent weight of grain. In a traditional hay/grain diet, horses utilise between 50 and 60% of the energy, whereas they utilise 85-90% of the energy in oil. A high-oil diet works best in conjunction with a high carbohydrate intake and there is no benefit in feeding more than 10% oil in the total diet. There are opinions that suggest a high oil intake compromises intense muscular exercise. However, this has not been observed when oil intake is at the levels given above and when adequate carbohydrate is available.
Another advantage of oil-adaptation is a reduction in metabolic heat generation both at rest and during exercise. Because a major source of heat production is the digestive system, when selecting feeds, their difference in waste heat production should be considered in relation to climate and work load. In one study, feeding extra oil resulted in a 14% decrease in total heat production and as a result, over 60% more energy was available for exercise or weight gain. Because horses produce less body heat when they burn fat as a fuel, the heat load is further reduced. This indirectly reduces stress on the respiratory system of the racing standardbred, because during intense exercise the respiratory system is an important means of heat reduction.
During training and racing, standardbreds can lose up to 12 litres of fluid and 120 grams of electrolytes. Reducing and preventing dehydration secondary to sweat losses, is a constant and ongoing challenge for the horse and the trainer. If heat stress is severe, horses may become 'dry coated', lose the ability to sweat and overheat.
Electrolyte deficiency increases the incidence of tying up, blood thickening, impaction colic and reducing urine production and the ability to sweat. Electrolytes should never be added to the drinking water unless fresh water is available, as this prevents the horse from regulating its body fluid levels. Thirst occurs when there is excess sodium in the body. If the drinking water contains sodium, the horse cannot restore the balance as drinking will increase sodium intake. Affected horses will drink and urinate excessively. If this vicious cycle continues, the horse will lose weight. The weight loss is frequently blamed on the feed - preventing recognition of the true cause.
Many horses are still fed according to traditions developed over 100 years ago in cold regions of the northern hemisphere. In hot climates, the benefits of oil-enriched feeds, correctly profiled for amino acids and protein and of steam-extruded grains are well-recognised. Mitavite has an ongoing commitment to research in nutrition and exercise physiology in hot climates. Combining the most update research findings with time-honoured traditions and practices, Mitavite has included Protexin in XLR8 further fine-tuning racing feeds to meet the stress endured by horses training and racing in hot/humid climates.
Talk to the team at your local RD1 store today about the range of Mitavite products available and which are best suited for use through the summer months.
Some products may not be available in all stores but can be ordered on request.
Disclaimer: Any views and comments expressed in this article are not necessarily the opinions of RD1 Limited nor associated agencies. This content is copyright of RD1 Limited.
