Analyze Hay to Understand Quality

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While spring and early summer--with grass abundant and rain seemingly constant--seem a strange time to be talking about hay, now is the time when hay crops are being cut and stored. And this is the time of year farm and stable owners and managers are (or should be) seeking out a quality hay supply for this fall and winter. This critical part of your horses' diets needs to have as much attention paid to is as selecting and buying the right concentrate feeds and supplements. Unfortunately many owners and managers simply buy on past performance, or take what they can get. Laurie Lawrence, PhD in equine nutrition, of the University of Kentucky College of Agriculture, discusses hay testing and what it means to your horses.

Hay is an important component of horse rations, particularly in the winter when fresh pasture is not available.

One way to evaluate the quality of hay is to get it analyzed. There are many different types of analyses available, and the cost can range from $10-$20 per sample to more than $100. The most extensive analysis will report more than 20 different nutrients or chemical fractions.

Although this detailed information makes sense to nutritionists, it is often not helpful to someone who wants to compare the values of different hays, or someone who wants an overall assessment of the nutritional value of the hay. To simplify the interpretation of hay analyses, nutritionists have come up with equations to give more general estimates of forage quality. One estimate of quality is relative feed value (RFV).

RFV was developed for cattle and takes into account the expected digestibility of the hay as well as the expected level of consumption. Basically, the assumption is that the better the quality of hay, the more easily the animal will digest it and the more it can consume. The estimates of digestibility and intake are calculated from the concentration of neutral detergent fiber (NDF) and acid detergent fiber (ADF) in the hay. As a forage plant matures, it becomes more fibrous and stemmy, which results from increased concentrations of NDF and ADF. So, as NDF and ADF increase, RFV decreases.

The table below shows the composition of some common forages used for horses in Kentucky. The RFV is calculated from the equations developed for cattle (no equations currently exist for horses). You can discuss common forages in your state or region with your county extension agent, ag college nutritionist or equine nutrition specialist.

Types of Hay CP** NDF ADF RFV

Grass* Hay; very mature, large seed heads 7.0% 63.9% 41.1% 83

Timothy Hay; early maturity, few small seed heads 11.7% 53.1% 34.0% 109

Grass Hay-Alfalfa Hay Mix; mid maturity 14.1% 52.1% 36.7% 108

Alfalfa Hay; full bloom, some leaves, large stems 16.0% 49.8% 42.8% 104

Alfalfa Hay; mid-bloom, leafy, medium stems 18.2% 44.9% 36.1% 125

Alfalfa Hay; early bloom, leafy, small stems 21.7% 39.0% 30.2% 156

Alfalfa Cubes ( bagged) 21.1% 42.4% 33.5% 138

* Examples: orchardgrass or timothy

** All compositions are shown on a 100% dry basis.

RFV does not exactly apply to horses, but it can provide a basis of comparison between different hays, particularly hays of the same type. For example, if you had a choice between a full-bloom alfalfa hay with an RFV of 100, or a mid-bloom alfalfa hay with an RFV of 125, you could be pretty certain the latter hay would have a higher feeding value.

Ideally you would like to know that the second hay provides 25% more value than the first hay, but RFV estimates are not that accurate for horses. Nonetheless, if the two hays are the same price, the one with the higher RFV will usually provide more nutrition for the dollar. 

What RFV should you purchase?

The answer to this question depends upon the type of horse being fed, as well as the price of the hay. Hay with high RFV is most appropriate for horses with high nutrient requirements, such as lactating mares, growing horses and some performance horses. The higher the RFV of a hay, the less you will need to feed. In addition, as the RFV of the hay increases, the amount of concentrate (sweet feed, grain or pelletized feeds) needed will decrease. So, when choosing between two similarly priced hays, the one with the higher RFV may reduce total feed costs by reducing the amount of concentrate that is fed.

However, hay with a very high RFV isn’t necessarily the “best” hay for every horse. If a mature, idle horse with low nutrient requirements is given unrestricted access to hay with high RFV, it will probably become very fat. At a normal rate of intake, hay with a moderate RFV might be best for idle, mature horses. Hay with a moderate or low RFV value may be desirable for horses with low nutrient requirements, because they can eat enough to satisfy their hunger without gaining too much weight.

Although RFV can give a general idea about forage quality, it does not give an estimate of how closely the hay will satisfy an animal’s nutrient requirements. RFV is calculated only from the amount of fiber in the hay and does not address the amount of protein, calcium, phosphorus or other important nutrients needed by horses.

RFV is a calculated value from a laboratory analysis of fiber concentrations in a hay sample. It does not provide any information on the cleanliness of the hay.

Regardless of RFV, horse hay should be free of dust and mold. Horses are susceptible to respiratory irritation from moldy and dusty hay, and this irritation can affect exercise performance. Therefore, when purchasing hay, both a visual inspection and a laboratory analysis of the composition should both be considered in evaluating its value.