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Part 2. Balancing Equine Diets
Nutritional imbalances can be a factor in many equine health issues, as discussed in Part 1 and in this article on nutrition basics by Kellon (2014). In this section, we will show you how to balance your horse's diet based on hay and pasture samples from Harrison County, Indiana (Fig. 1).
Nutritional imbalances can be a factor in many equine health issues, as discussed in Part 1 and in this article on nutrition basics by Kellon (2014). In this section, we will show you how to balance your horse's diet based on hay and pasture samples from Harrison County, Indiana (Fig. 1).
Fig. 1. Google map showing approximate location of hay and pasture samples in Harrison County, Indiana.
The strategy is to determine a base diet from good quality grass hay and/or pasture and then correct for deficiencies and excesses in terms of macronutrients (major elements), micronutrients (trace elements), digestible energy (calories) and crude protein (nitrogen (N) content). The procedure is actually very straightforward and consists of comparing your hay and pasture analysis to the nutrient requirements published by the National Research Council (NRC, 2007) after applying constraints on mineral ratios. These constraints are necessary because of antagonistic effects, i.e., the negative effect of one element (mineral) on the absorption of another mineral. A good example is iron (Fe), which is in excess of NRC requirements in almost all feeds and supplements. Excessive amounts of iron limit the absorption of zinc, and possibly copper, and are associated with iron overload, insulin resistance and infection and immunity.
Let’s get started. The first piece of information you will need is the nutrient profile of your grass hay and pasture. All hay and pasture analyses on this page have been determined by Equi-analytical Laboratory, Ithaca, New York, a division of Dairy One. Go to their web site for information on sampling procedures. Table 1 below shows results from Equi-analytical for grass hay and pasture samples collected near Central, Indiana. Hay sample is first cutting baled in May 2013; pasture sample was collected in October 2013.
Complete sample analyses as received from Equi-analytical are attached at the end of this section as Appendix 1. We have also recently uploaded some examples of hay analyses (minerals, crude protein, neutral detergent fiber and digestible energy) from Harrison and adjacent counties in Indiana and Kentucky (Appendix 2).
Let’s get started. The first piece of information you will need is the nutrient profile of your grass hay and pasture. All hay and pasture analyses on this page have been determined by Equi-analytical Laboratory, Ithaca, New York, a division of Dairy One. Go to their web site for information on sampling procedures. Table 1 below shows results from Equi-analytical for grass hay and pasture samples collected near Central, Indiana. Hay sample is first cutting baled in May 2013; pasture sample was collected in October 2013.
Complete sample analyses as received from Equi-analytical are attached at the end of this section as Appendix 1. We have also recently uploaded some examples of hay analyses (minerals, crude protein, neutral detergent fiber and digestible energy) from Harrison and adjacent counties in Indiana and Kentucky (Appendix 2).
For those who prefer not to work through the diet calculations, here's the take-home message.
1. Grass hay and pasture in Harrison County, Indiana are deficient in copper, zinc, sodium and manganese (pasture only). Selenium meets the minimum requirement established by the National Research Council (Nutrient Requirements of Horses, 2007).
2. If these minerals are supplemented at recommended levels, horses at average activity levels (pleasure) and working horses (moderate workload) can be maintained on grass hay and pasture, respectively.
3. High-iron hay and pasture require correspondingly higher levels of supplementation because iron limits the absorption of certain trace minerals, such as zinc.
4. Analyze your hay before purchase and, if possible, choose high-quality hay with relatively low iron content (< 100 ppm).
5. The nutrient content of hay and pasture will vary based on soil type, farming practices and type of grass, or other pasture plants. Therefore, it is important that you balance your horse's diet based on forage from your local area.
To simplify the calculations, we will consider only two NRC horse classes:
1. Average maintenance, which would apply to most pleasure horses in Harrison County, Indiana (NRC Average Maintenance: average alertness, mood and activity levels on turn out);
2. Moderate work, a workload characteristic of some endurance horses, or horses in training (NRC Moderate Work: 3 to 5 hours per week; 30% walk, 50% trot, 10% canter, 5% low jumping, cutting or other skill work).
Formulae are available from NRC to calculate nutrient requirements but for convenience we will use their online software. Initially, we will also assume that both horses in our calculation weigh 500 kg (1100 lbs) and that both horses are in good health. Table 2 lists their NRC estimated daily nutrient requirements.
1. Average maintenance, which would apply to most pleasure horses in Harrison County, Indiana (NRC Average Maintenance: average alertness, mood and activity levels on turn out);
2. Moderate work, a workload characteristic of some endurance horses, or horses in training (NRC Moderate Work: 3 to 5 hours per week; 30% walk, 50% trot, 10% canter, 5% low jumping, cutting or other skill work).
Formulae are available from NRC to calculate nutrient requirements but for convenience we will use their online software. Initially, we will also assume that both horses in our calculation weigh 500 kg (1100 lbs) and that both horses are in good health. Table 2 lists their NRC estimated daily nutrient requirements.
You can construct a table showing daily nutrient intake based on your hay and grass analyses using some simple math. Multiply the percentages in Table 1 by 10 to convert to g/kg (grams per kilogram forage). In our example, we are assuming that each horse consumes 2% BW (body weight) per day (0.02 x 500 kg = 10 kg) so the g/kg value determined above is multiplied by 10 to find total dietary intake per day. For example, 0.49% x 10 = 4.9 g Ca/kg forage. For 2% BW, 4.9 g/kg x 10 kg (22 lbs) = 49 g Ca per day. Since concentrations for the trace elements are already expressed in terms of mass units (mg/kg), simply multiply these values by 10. For example, 8 mg/kg Cu x 10 kg = 80 mg Cu per day. The results for our hay and pasture analyses are listed in Table 3.
Because the water content of grass usually makes up about 70-90% of the total weight of the sample, results for pasture grass are calculated on a dry matter basis (100% dehydrated sample, or 0% moisture). Unfortunately, unlike with hay, we cannot control, or determine, how much grass a horse consumes per day. As a result, the nutrient amounts shown in Table 3 are theoretical values, or educated estimates. A horse on 24/7 turn out would have to consume more grass than the kg dry matter amount in our calculation because of the high moisture content of grass. Refer to the equi-analytical web site for a more detailed discussion of "as sampled" versus "dry matter" results and the pasture analysis in Appendix 1.
At this point, we balance nutrients based on several mineral constraints (Eleanor Kellon, VMD, Equine Nutrition Courses). To compensate for Fe excess, the Fe:Cu ratio is set to 4:1 and the target values for Cu:Zn:Mn to 1:3:3. For the hay analysis, Cu concentration is Fe/4 = 190 and Cu:Zn:Mn = 190:570:570. The corresponding ratio for grass pasture is 315:945:945. Ideally, target values for the ratios Ca/Mg and Ca/P should be within the range 1.5 to 2.0:1. For our hay and grass samples, the unconstrained ratios are Ca/Mg = 3.06, Ca/P = 1.63 and Ca/Mg = 2.7, Ca/P = 1.5, respectively.
Final results are summarized in Table 4 after balancing on Fe and rounding off to the tenths place. In this example, we will assume that the diet of the pleasure horse is grass hay only and the working horse (endurance) is 24/7 pasture.
At this point, we balance nutrients based on several mineral constraints (Eleanor Kellon, VMD, Equine Nutrition Courses). To compensate for Fe excess, the Fe:Cu ratio is set to 4:1 and the target values for Cu:Zn:Mn to 1:3:3. For the hay analysis, Cu concentration is Fe/4 = 190 and Cu:Zn:Mn = 190:570:570. The corresponding ratio for grass pasture is 315:945:945. Ideally, target values for the ratios Ca/Mg and Ca/P should be within the range 1.5 to 2.0:1. For our hay and grass samples, the unconstrained ratios are Ca/Mg = 3.06, Ca/P = 1.63 and Ca/Mg = 2.7, Ca/P = 1.5, respectively.
Final results are summarized in Table 4 after balancing on Fe and rounding off to the tenths place. In this example, we will assume that the diet of the pleasure horse is grass hay only and the working horse (endurance) is 24/7 pasture.
Interpreting Table 4 results
1. With the exception of Cu and Zn, our grass hay sample provides all of the mineral, protein and calorie requirements for adult horses at average maintenance. The Ca/Mg ratio is slightly high but tolerable. Supplementing with additional Mg to reach our target value (2:1) would require 8.5 g Mg.
2. Working horses (moderate level) grazing our pasture 24/7 require supplementation with Cu, Zn, Mn and possibly Se (not analyzed). The addition of 7 g Mg to the diet would be needed to achieve the 2:1 target value for the Ca/Mg ratio.
3. In addition to the mineral deficiencies noted above, hay and grass pasture in Harrison County, Indiana are particularly low in Na (compare Tables 2 and 3).
4. In cases 1 and 2 above, with the exception of Na and Se, major and trace elements are approximately equal to, or exceed, 150% NRC minimum requirement. This safety margin ensures that we have compensated for metabolic differences among horses as well as inaccuracies in analytical results and sampling errors.
5. A number of grass hays that we have tested have Fe concentrations exceeding 200 ppm. In these cases, balancing on Fe will significantly increase the amount of Cu and Zn required to reach the target ratio 4:1:3:3 for Fe:Cu:Zn:Mn. Analyze hay before purchasing and choose good quality hay with relatively low Fe concentration (< 100 ppm). This will be more cost effective because less Cu/Zn supplementation is required to correct deficiencies.
6. The nutrient profiles of hay and pasture will vary based on soil type, pasture fertilization and type of grass, or other pasture plants. Therefore, it is important that you balance your horse's diet based on forage from your local area.
Keep in mind that balancing software is only a tool and diet must be evaluated on a regular basis in terms of body weight and condition score. For some good photographs with comments by Don Henneke, Ph.D. (author of the Henneke condition scoring system) download this PDF on body condition scores. A short video on the proper way to estimate your horse's weight can be found here.
In Part 3, we will discuss how to choose and formulate your own supplements.
1. With the exception of Cu and Zn, our grass hay sample provides all of the mineral, protein and calorie requirements for adult horses at average maintenance. The Ca/Mg ratio is slightly high but tolerable. Supplementing with additional Mg to reach our target value (2:1) would require 8.5 g Mg.
2. Working horses (moderate level) grazing our pasture 24/7 require supplementation with Cu, Zn, Mn and possibly Se (not analyzed). The addition of 7 g Mg to the diet would be needed to achieve the 2:1 target value for the Ca/Mg ratio.
3. In addition to the mineral deficiencies noted above, hay and grass pasture in Harrison County, Indiana are particularly low in Na (compare Tables 2 and 3).
4. In cases 1 and 2 above, with the exception of Na and Se, major and trace elements are approximately equal to, or exceed, 150% NRC minimum requirement. This safety margin ensures that we have compensated for metabolic differences among horses as well as inaccuracies in analytical results and sampling errors.
5. A number of grass hays that we have tested have Fe concentrations exceeding 200 ppm. In these cases, balancing on Fe will significantly increase the amount of Cu and Zn required to reach the target ratio 4:1:3:3 for Fe:Cu:Zn:Mn. Analyze hay before purchasing and choose good quality hay with relatively low Fe concentration (< 100 ppm). This will be more cost effective because less Cu/Zn supplementation is required to correct deficiencies.
6. The nutrient profiles of hay and pasture will vary based on soil type, pasture fertilization and type of grass, or other pasture plants. Therefore, it is important that you balance your horse's diet based on forage from your local area.
Keep in mind that balancing software is only a tool and diet must be evaluated on a regular basis in terms of body weight and condition score. For some good photographs with comments by Don Henneke, Ph.D. (author of the Henneke condition scoring system) download this PDF on body condition scores. A short video on the proper way to estimate your horse's weight can be found here.
In Part 3, we will discuss how to choose and formulate your own supplements.
Appendix 1. Sample analyses as received from Equi-analytical
Mixed grass hay; square bales, first cutting, drying time 4 days. Mulitply Mcal/lb, g/lb and mg/lb by 2.2 to obtain equivalent values in kg, e.g., Mcal/kg. For hay, diet balancing is based on "As Sampled", rather "Dry Matter" results. This is what you are feeding your horse.
Mixed grass pasture collected in October on mild (High 16 C = 60 F, Low 4 C = 40 F), cloudless day at peak carbohydrate levels (4:00 PM). Because of the high moisture content of grass, "Dry Matter" results are used in diet calculations with pasture grass.
Appendix 2a and Appendix 2b: Examples of hay analyses from Harrison and adjacent counties comparing mineral concentrations, crude protein, neutral detergent fiber and digestible energy (calories). Several "speciality" hays are included for comparison.
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