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.

Thus, 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 concentrates.
  • Certain nutrient requirements may be met by forage alone; however, there are a number of nutrients generally not found in forages in sufficient quantities to meet requirements.
  • We must understand what the forage is providing in order to select the appropriate concentrate.

Total Intake:

Total intake is determined by calculating the amount of each nutrient that is supplied by all feed consumed by the horse – hay, pasture, concentrate and supplements.

Once determined, total nutrient intake can then be compared against the nutrient requirement recommendations put forth by the National Research Council in The Nutrient Requirements of Horses (NRC 2007). Emphasis on the fact that these are recommendations based on the available published literature at the time of publication. The optimal amount of nutrient intake may be higher than the recommendation, which is by definition the amount required to prevent symptoms of deficiency. A number of nutrients do not have defined requirement recommendations, therefore interpretation of dietary intake is more subjective; however, the absence of a requirement recommendation does not mean that a requirement does not exist, rather that the research to determine a value was not available.
Although feed tags and forage analysis report nutrient concentration (% or ppm), nutrient requirements are a recommended daily intake (g or lb). In order to compare dietary intake to daily requirements, the amount of a given nutrient supplied by the total diet must be determined. The amount of a given nutrient supplied by a feed is calculated as follows:

Amount of feed being fed (lb or kg) x Concentration of nutrient in feed (%, ppm) = nutrient intake

When comparing various products, nutrient concentration and suggested daily product volume should both be considered. Oftentimes, supplement guarantees are reported as concentration per pound, which looks impressive, and suggested feeding rate is several ounces per day which ultimately supplies negligible amounts of nutrients.


It can’t be stressed enough that for most horses forage makes up the majority of the diet and forages are a major nutrient source. A common question we get when a horse is not maintaining weight or has decreased performance is “what changed with the feed”. Ultimately, the variation in a fixed formula is going to be extremely small. Ingredients are used at set amounts and incoming ingredients are required to fall within strict parameters. Forages on the other hand are very dynamic and generally not tested. Hay from the same field can vary considerably from cutting to cutting, year to year, or even across different areas of a field. While a hay analysis for every load would be ideal, it is not often feasible; however, forage quality should be explored when animal performance changes considerably. Potential impacts of changes in health, workload or management should also be considered.  

Average values for hay varieties are available in the NRC as well as through several other sources; however, due to the nature of the variability of nutrients in hay average values are of limited value. Particularly when formulating diets for reproducing and growing horses or trouble shooting poor performance a hay analysis is strongly recommended. Hay analyses are inexpensive relative to the value of the information gathered. A number of commercial laboratories offer hay analysis services, with some offering specific analytic packages tailored towards horses. Proper sampling technique is key to ensuring a useful analysis is generated and the sample should be representative of the entire lot. Use of a bale corer is recommended and sampling 10% of the bales in a lot.

The following figures (Figures 1-4) give examples of the nutrients supplied through “average” forage at differing levels of production and intake. Recognize that these values are likely not an exact representation of the hay in your own loft.

Figure 1. Idle, mature horse fed 2.0% of body weight as grass hay

Figure 2. Idle, mature horse fed 2.0% of body weight as legume hay

Figure 3. Lactating mare fed 2.5% of body weight as grass hay
Figure 4. Lactating mare fed 2.5% of body weight as legume hay

The appropriate concentrate to complement the examples above varies with the forage type. Forage type should be of particular note for reproducing and growing horses, with care taken to account for the mineral profiles of primarily grass versus primarily legume forages. The majority of commercial products are formulated to balance a grass-type forage. Diets containing greater than 50% legume should be paired with a product specifically designed to complement legume forages. Notably, some nutrients are not supplied in sufficient quantities in hay regardless of quality. For example, fat soluble vitamin degradation occurs rapidly after harvest.
Further, product selection should match stage of production to account for differences in nutrient requirements. Figure 5 details the changes in nutrient requirements through gestation. Feeding a greater quantity of a product formulated for all-stages may allow for the increased energy demand to be met but would be unlikely to meet the increased demand for fetal development.

Figure 5. Percent change in nutrient requirements during gestation over an open mare

Finally, the examples above do not account for the complex relationships between site of digestion and nutrient interactions when accounting for nutrient supply. It is possible to supply sufficient quantities of a nutrient in a mature forage, but due to advanced lignification foregut availability of that nutrient will be poor and the majority of nutrients are absorbed in the foregut of the horse. Similarly, mineral antagonism and competition for uptake at the transporter level can result in a biological deficiency even if a diet supplies adequate amounts on paper.

Nicole Rambo, Ph.D.