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January 01, 2017

Total Diet of the Horse

It is important to realize that forages (hay and pasture) provide a significant portion of the horse’s daily nutrient requirements. Proper nutritional principles require that we recognize the contribution of forages and adjust the concentrate (grain) portion of the diet accordingly to meet the horse’s requirements. Recommending a feed and/or supplement without assessing the TOTAL DIET may adversely affect the horse’s health and performance.

Selection of the concentrate and/or supplement should be based on the forage being fed and supply the portion of the horse’s requirements NOT met by that forage. Furthermore, adding supplements to the horse’s diet is more a rule than an exception in today’s horse industry. So understanding how to assess the total diet is the responsible path to follow.

KEY POINTS:

  • All feedstuffs offered to horses have SOME level of MOST nutrients.
  • Horses typically consume more forage than concentrate (grains). Consider the contribution of your forage to meeting your horse’s requirements.
  • Certain nutrient requirements may be met by the forage alone.
  • We MUST understand what the forage is providing before designing or selecting the appropriate concentrate.
  • The nutrient requirements of the horse are determined by the National Research Council (NRC) Committee on Horse Nutrition (2007).

DETERMINING TOTAL INTAKE

TOTAL INTAKE is determined by calculating the amount of each nutrient that is supplied by ALL FEEDS offered to the horse – hay, pasture, grain and supplements.

There are commercially available software programs to do these calculations and compare them to NRC 2007 requirements without the tedious calculations outlined below1, but we desired to explain the process. 

Note – calculations for nutrients whose requirements are not addressed by NRC 2007 will be the same as described here, but the relevance is more subjective. Nutrients such as starch, sugar (NSC – nonstructural carbohydrates = sugar + starch), ADF (acid detergent fiber), NDF (neutral detergent fiber), lignin and ash may have value, but no established requirements exist. Values for certain vitamins, minerals and amino acids are often listed on feed tags, but, again, assessing the relevance is purely speculation when no requirement has been established. Nutrient concentration values for forages can be obtained most accurately by laboratory analysis, but NRC and other database values can be used in lieu of laboratory analyses. Most laboratories have information on proper sampling techniques for hay, pasture and concentrates. Valid results are only obtained when proper sampling techniques are followed. Nutrient concentration values for grains, concentrates and supplements will be found on the product labeling, but can also be submitted for laboratory analysis. TAKE CARE TO NOTE POSSIBLE DIFFERENCES IN LABEL CONCENTRATIONS WITH RESPECT TO FEEDING RECOMMENDATIONS, especially with supplements. Supplement concentrations are often listed as “per pound” but feeding recommendations are in ounces or grams.

In general, how is the amount of nutrient supplied by a feed calculated?

AMOUNT OF FEED BEING FED (pounds or kilograms) x CONCENTRATION OF THAT NUTRIENT IN THE FEED (i.e. % or mg/kilogram).

The charts on the following pages demonstrate the contribution of grass or legume hay to meeting the NRC 2007 nutrient requirements of either an idle, mature horse or a lactating mare. As you can see, the gap between the NRC requirement (depicted as the “100%” line) and what is supplied by the forages varies with the type of animal and the forage source.

CHART 1: Idle, Mature Horse Fed 2.0% of Body Weight as Grass Hay

CHART 2: Idle, Mature Horse Fed 2.0% of Body Weight as Legume Hay

CHART 3: Lactating Mare Fed 2.5% of Body Weight as Grass Hay

CHART 4: Lactating Mare Fed 2.5% of Body Weight as Legume Hay

SPECIFIC CALCULATIONS

  • Assessing Digestible Energy Supplied

Digestible energy (D.E.) concentration of a feed is expressed in a forage analysis or on a feed tag as Mcal/pound or Mcal/kg with daily requirement expressed as Mcal.

The amount of Digestible Energy in Mcal supplied by a feed is: 

Mcal/pound x pounds of feed = Mcal 
or 
Mcal/kg x kg of feed = Mcal

EXAMPLE: a client is feeding 15 pounds (6.8 kg.) of a grass hay with a D.E. of  0.8 Mcal/pound (1.76 Mcal/kg.):

The amount of Digestible Energy in Mcal supplied by a feed is:

0.8 Mcal/pound x 15 pounds of hay = 12 Mcal
or
1.76 Mcal/kg x 6.8 kg of feed = 12 Mcal

  • Assessing Crude Protein, Lysine, Calcium, Phosphorous, Magnesium, Potassium, Sodium, Chlorine or Sulfur Supplied

The concentration these nutrients in a feed is expressed in a forage analysis or on a feed tag as a PERCENT (%) with daily requirement expressed as GRAMS (g).

The amount of these nutrients in grams supplied by a feed is: 

% nutrient (as decimal) x pounds of feed x 454 g/pound = grams
or
% nutrient (as decimal) x kg of feed x 1,000 g/kg = grams

EXAMPLE: a client is feeding 5 pounds (2.3 kg.) of a grain mix that is 1.2% calcium:

The amount of Calcium in grams supplied by this feed is:

0.012 (decimal for 1.2% Ca) x 5 pounds of feed x 454 g/pound = 27 grams
or
0.012 (decimal for 1.2% Ca)) x 2.3 kg of feed x 1,000 g/kg = 27 grams

  • Assessing Cobalt, Copper, Iodine, Iron, Manganese, Selenium, Zinc, Thiamine or Riboflavin Supplied

The concentration these nutrients in a feed is expressed in a forage analysis or on a feed tag as parts per million (ppm) or mg/kg with daily requirement expressed as mg.

The amount of these nutrients in mg. supplied by a feed is:

mg/kg (or ppm) x (pounds of feed/2.2pounds/kg) = mg
or
mg/kg (or ppm) x kg of feed = mg

EXAMPLE: a client is feeding 2 pounds (0.91 kg.) of a supplement with a copper concentration of 200 mg/kg:

The amount of these copper in mg. supplied by this feed is:

200 mg/kg (or ppm) x (2 pounds of feed/2.2pounds/kg) = 182 mg
or
200 mg/kg (or ppm) x 0.91 kg of feed = 182mg

  • Assessing Vitamin A, D or E Supplied

The concentration Vitamins D and E in a feed is expressed in a forage analysis (very seldom are vitamins included in forage analysis due to the expense) or on a feed tag as International Units (IU)/pound with daily requirement expressed as IU. Vitamin A requirement is listed as kIU (IU x 1,000)

The amount of Vitamin A, D or E in IU supplied by a feed is:

IU/pound x pounds of feed = IU
or
IU/pound x (kg of feed x 2.2 pound/kg) = IU

EXAMPLE: a client is feeding 5 pounds of a concentrate with a Vitamin A concentration of 4,000 IU (4 kIU)/pound

The amount of Vitamin A in IU supplied by this feed is:

4, 000 IU/pound x 5 pounds of feed = 20,000 IU (20 kIU)
or
4,000 IU/pound x (2.3 kg of feed x 2.2 pound/kg) = 20,000 IU (20 kIU)

  •     Using the above calculations or a software program, include assessment for all nutrients of interest for the forage, concentrate/grain, as well as any supplements provided to the horse. Total the amounts for each feed and compare to the horse’s requirement in NRC 2007.
  •     For specific nutrient requirements of horses see NRC Nutrient Requirements of Horses, 6th Edition.  The NRC Model program is available online at http://nrc88.nas.edu/nrh/ and can be used to generate requirements for specific classes of horses.

Many equine practitioners as well as horse owners only concern themselves with the CONCENTRATION of a nutrient, especially protein and starch, without regard to the AMOUNT of the feed offered to the horse. 

As you can appreciate, the CONCENTRATION of a nutrient is only one step in the analysis – by varying CONCENTRATION and AMOUNT, the horse’s requirement can be met by feeds with nutrient higher concentrations by feeding less feed or vice versa.

SUMMARY

  • Proper nutritional guidance can only be offered when the TOTAL DIET of the horse is considered.
  • Include assessment of all sources of nutrients offered to the horse, including forages, concentrates and supplements.
  • Over feeding most nutrients is, at a minimum, wasteful, but can also affect the health and general well-being of the horse
  • Commercial Ration Evaluation Software:
  1. Creative Formulations Concepts, LLC. Horse Ration Formulation – 2007; 1831 Forest Drive, Suite H, Annapolis, Maryland 21401 USA, http://www.agri-data.com/
  2. Equi Balance SoftwarePerformance Horse Nutrition, 967 Haas Road · Weiser, ID 83672,  http://www.performancehorsenutrition.com/

SUGGESTED READING
NRC Nutrient Requirements of Horses.  Sixth Revised Edition.  National Academy Press.  2007.