<p>A number of systems exist to calculate the requirements for nutrients and energy of  different categories of horse. Not only are the predominant breeds and the climates they live in different, but the way nutritionists express their requirements also differs greatly. This can be confusing to the horse owner interested in trying to calculate the requirements of energy, protein and minerals for his/her horse, especially when trying to compare requirements across national borders or to communicate standards of energy and protein requirements under circumstances where the basis for the calculation of requirements differs. Different methods may also express the same requirement in different ways and with different units. For example: requirements of energy may be expressed as <em>digestible energy</em>, metabolisable energy or net energy, and even more confusingly, the units of energy themselves may be expressed in <em>Megacalories (MCal)</em>, <em>Megajoules (MJ)</em> or <em>Feed units</em>.</p>
<p>The rules (equations) for the calculation of energy requirements are derived from large-scale digestive trials with horses and other farm animals. Fortunately, it is possible to interconvert requirements expressed as digestible, metabolisable or net energy terms from one to the other, and to re-calculate from megacalories into feed units or megajoules.</p>
<p>The PC-Horse program allows the user to select between the two most important systems presently used throughout the world to calculate protein and energy requirements: <br /><br />1: The "European standard" is based on the system for energy and protein requirements for horses developed in France over the last 20 years, and further adjusted by the Dutch. This system is presently recommended by a Nordic group of scientists as a common standard for the Nordic countries. The "European standard" is the default choice for versions of the PC-Horse program compiled for sale in European countries. Apart from energy and protein, PC-Horse uses the NRC system (see below) for minerals and vitamins. <br /><br />2: The National Research Council recommendations (NRC 2007) are developed in the USA and used in many other countries worldwide. The NRC system expresses protein requirements as crude protein.</p>
<p>In the European countries we have chosen to express the requirements for protein as digestible protein, which is a more biologically relevant entity than crude protein, since the latter only takes into account the nitrogen content of the ration. PC-Horse  is delivered to license-holders with feed lists that are matched to their corresponding energy and protein calculations. In the Consultant version, you may re-calculate the nutrient concentrations among the two systems. When importing feeds into PC-Horse, it is important for the user to ascertain that feed analyses and nutrient requirements are expressed in the same units.</p>
<p>For more information on the units that PC-Horse is using, see the "configure page" of the program.</p>
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