Interpreting hay analysis results
Digestible Energy (DE)
This component doesn't get a lot of attention, but it's essentially the 'calorie count' for the hay. The units are megacalories per pound (Mcal/lb) of hay.
The daily energy requirement for the average adult horse who is not pregnant, nursing a foal, or doing any work (i.e., the horse's basal or maintenance requirement) is now estimated based on the horse's temperament and amount of voluntary activity.* Following are the recommended daily calorie intakes for maintenance for the average 1,000-lb horse:
Minimum (very calm, sedentary) = 13.7 Mcal/day
Average (alert, moderate activity) = 15.0 Mcal/day
Elevated (highly strung, very active) = 16.4 Mcal/day
* The 2007 National Research Council (NRC) guidelines use these definitions: Minimum maintenance applies to adult horses with a sedentary lifestyle, due either to confinement or to a docile temperament. Average maintenance applies to adult horses with alert temperaments and moderate voluntary activity. Elevated maintenance applies to adult horses with nervous temperaments or high levels of voluntary activity.
The recommended daily intake of forages is approximately 2% of the horse's ideal body weight. For the average 1,000-lb horse who is neither under- nor overweight, that's approximately 20 lbs of hay per day if the horse has little or no pasture access for whatever reason.
So, if most or all of the horse's forage intake is hay, and we want to meet but not exceed the recommended daily calorie intake for maintenance, then look for a hay whose DE content is between 0.70 and 0.83 Mcal/lb (as sampled). That range covers the spread from the very sedentary horses (who need fewer calories) to the very active horses (who need more calories).
Note that these are recommendations for horses who don't do much and don't have any special needs. Horses who are growing, pregnant, nursing a foal, in work, or recovering from serious debility need more calories, and they can usually tolerate and benefit from forages with a higher DE content than the range recommended here.
As for inactive, overweight horses at risk for laminitis, more guidance is to be found in the specific carbohydrate components of the report.
Incidentally, except for % moisture, I typically look at the As Sampled columns of figures rather than the Dry Matter columns. When comparing hay with pasture samples, it's important to use the Dry Matter values, as they've taken the water content of the different feeds out of the equation so that we can compare 'apples with apples.' However, when looking at a hay sample for an individual or a group of horses, I'm most interested in what the horses will be eating, in the form they'll be eating it (moisture included), so I use the As Sampled values. As long as the hay is less than 10% moisture, I haven't run into any problems with this approach.
Digestible Energy (DE)