The best diet for a horse is a balanced diet based on data from a pasture or hay test (whichever is applicable). Symptoms like a dull coat, poor hoof quality, less than optimal performance and a weak immune system are the more obvious signs.
A balanced diet is essential for performance and in preventing health issues. So what is a balanced diet?
A balanced diet is one where all the nutrients are more than adequate to avoid deficiencies and the amount of minerals avoid competition with another. One example is copper and zinc, too much zinc in the diet has been found to interfere with the uptake of copper. Another is calcium and phosphorus, too much calcium can interfere with phosphorus and vice versa. There are many other examples.
The cheapest, easiest and most accurate way to find out the level of nutrients in your horse's diet is to test the main forage whether that be hay or pasture.
To determine whether nutrient levels are sufficient and balanced in a horse’s diet, the amounts consumed from forage, feeds and supplements can be compared with the amounts recommended in the 2007 Nutrient Requirements of Horses, 6th Edition by the National Research Council (NRC), the reference for equine nutritionists. Providing an insurance buffer by using at least 150% of NRC target minimums and keeping mineral ratios in a tight range will protect the horse from suboptimal intakes of trace minerals.
Manufacturers of feeds and supplements should supply a nutrient profile of their products when requested. With pasture or hay, the nutrient levels cannot be guessed by simply looking at it or comparing it with similar looking examples. Improved pastures tend to be higher in protein compared to native pastures but the levels of minerals do not fit a pattern. Previous land use, fertiliser history, plant species, soil type and acidity/pH will influence mineral levels. The cheapest, easiest and most accurate way to find out the level of nutrients in your horse's forage is to send a representative sample to a laboratory for testing. To learn more about how to collect a representative pasture sample, see the article on pasture testing - Case study: 3 pasture tests.
Following is a short description of how a pasture or hay test can be used, space doesn’t allow for a full analysis.
Pasture test results – a paddock of diverse native grasses
A representative sample of highly diverse native grasses from a paddock near Canberra, ACT was sent to Equi-Analytical laboratory in the USA as it only costs around $38 USD for a nutritional profile. There are a number of excellent laboratories in Australia but unfortunately the cost for the same test is far more expensive, around $120 plus.
The ‘Dry Matter’ column is used for pasture and ‘As Fed’ column if this pasture had been harvested for hay.
This percentage refers to the amount of moisture in the sample when it was received by the lab. All moisture is removed for testing.
% Dry Matter
This portion of the sample contains carbohydrates, protein, fat and minerals.
Digestible Energy (DE)
Digestible energy gives the energy value of the feed, expressed as Mcal/kg. This mixed native grass has an energy value of 1.96 Mcal/kg or 8.2MJ/kg. To give an idea of what this means, a 500 kg horse in no work would need to consume 8.5 kg in dry matter to maintain a good weight, better known as body condition score. A horse in heavy work such as endurance or eventing would need to consume 14 kg in dry matter if no other feed was provided. If a test gives Metabolisable Energy (ME) it's for ruminants like cattle and is not applicable for horses.
Crude Protein (CP)
Rather than protein itself this measures the level of nitrogen and nitrates. Protein contains nitrogen so it's a useful indicator of protein, when the level of CP is considered high by a nutritionist then it's advised to get the sample tested for nitrates as high nitrate levels can cause health issues in horses. A nitrates test is $6 USD and can be ordered at any time. This native pasture indicates 131.7 grams per kg. 8.5 kg contains about 1120 grams, enough protein to support a 500 kg horse up to a very heavy workload.
Lysine is an essential amino acid which means it must come from the diet. It’s often called the limiting amino acid, if there is a lysine deficiency then the proteins that require lysine cannot be manufactured by the cells and the unused protein will be excreted, causing muscle building issues. This pasture is calculated to have 4.6 grams per kg which covers the lysine requirement but not by much. A small level of supplementation would be recommended to avoid topline issues.
The fibre factions; Acid Detergent Fibre (ADF) and Neutral Detergent Fibre (NDF) are very useful for evaluating the quality of hay.
Acid Detergent Fibre (ADF)
This gives a measure of two of the complex carbohydrates that make up the cell walls lignin and cellulose. Cellulose is broken down by micro organisms (fermented) in the hind gut but lignin is virtually nonfermentable. Lignin is a key component of wood. The lower the number, the more fermentable the fibre and the easier for nutrients to be extracted from the plant material.
Neutral Detergent Fibre (NDF)
This includes lignin and cellulose but also hemicellulose, another cell wall component. The lower the ADF and the higher the difference between ADF and NDF, the more fermentable the fibre. In this example, if this pasture had been harvested for hay at the time of testing ADF is 21 and NDF 39 indicating a very nice hay for horses. If the ADF was 39, it would mean it’s tougher to extract the nutrients.
WSC, ESC and starch can only be reliably tested in hay. When researchers test sugars and starch in pasture they immediately freeze the sample in liquid nitrogen to stop the sugars from metabolising further. Grass will continue to metabolise after it has been cut.
WSC (Water Soluble Carbohydrates)
These carbohydrates will dissolve to some extent in water and includes digestible sugars such as fructose, glucose, sucrose and indigestible plant sugars and some fructan.
ESC (Ethanol Soluble Carbohydrates)
ESC is a subset of WSC and includes sugars that are soluble in ethanol. ESC is important as this is the component that causes insulin to spike.
Starch is a complex carbohydrate made up of glucose sugars, it’s how plants store glucose. In animals glucose is stored as glycogen. For insulin resistant horses, glucose causes insulin to rise that may trigger the chain of steps resulting in laminitis. Dr Eleanor Kellon VMD advises to keep ESC + starch below 10% for the overall diet and individual feed ingredients. If this pasture was harvested at the time of testing it would have produced very low sugar + starch hay.
Non Fibre Carbohydrates (NFC)
This is calculated from adding starch to WSC and soluble fibres and plant sugars other than the simple digestible sugars. It includes all the carbohydrates that are not part of the cell wall of plants.
Calcium, phosphorus and magnesium are needed in gram amounts in the diet compared to the trace minerals which are only needed in small amount in miligrams. Many nutritionists aim for a calcium to phosphorus ratio between 1.2:1 to 2:1 though a higher ratio is considered to be okay, a ratio of 5:1 or higher is better to be temporary. A calcium to magnesium ratio is recommended to be between 1.5:1 and 2:1. This native pasture is fine for calcium up to a heavy workload for a 500 kg horse but phosphorus is very deficient. Supplementation of phosphorus will also improve the calcium to phosphorus ratio. The test indicates that magnesium levels are quite generous and will support a horse up to heavy work.
The levels of electrolytes; potassium and sodium are included. Sodium is very low and cannot support a 500 kg horse’s needs, even if the horse was in no work. It can be supplemented with table salt allowing for a generous buffer, especially if the horse is in a hot climate and sweats easily. 2 to 4 tablespoons per day is appropriate, the excess is easily and efficiently excreted. Potassium vastly exceeds a horse’s requirements which is the norm for pasture and hay so never needs supplementing for standing around in a paddock and sweat losses unless the horse has been exercised for more than 2 hours.
Smaller amounts are required but trace minerals are no less important than the major minerals and includes iron, copper, zinc and manganese. Many nutritionists support the ideal ratio of 1:3 for copper to zinc. In this grass sample the ratio of copper to zinc is 1:6 with both copper and zinc highly deficient for a 500 kg horse in no work. Needs rise with increasing workload so must be supplemented. Molybdenum is a trace mineral that needs to be noted, at high levels it can interfere with copper uptake. Both iron and manganese vastly exceed needs.
The results from a pasture or hay test can be used to choose the best feeds (if any are needed at all) and supplements to correct any deficiencies and correct the mineral ratios.
Originally published in the April - May 2010 (Vol 31 No 6) issue of Hoofbeats magazine.
Dr Sarah L. Ralston VMD Diagnosis of Nutritional Problems in Horses
Dr Eleanor Kellon VMD
The NRCPlus course goes into more detail discussing the merits of hair, soil, blood and tissue testing. Also explains how to read a hay or pasture test and design a diet based on the test.
Equine Cushings and Insulin Resistance Yahoo group. Dr Eleanor Kellon VMD contributes.