Question: Does my horse need hay in the summer? We have a large pasture. (I decided to address this topic after reading a question about it on Equisearch.com)

Answer: The answer is maybe. An adult horse will require an average of 1-5 acres of pasture to obtain adequate nutrition if being lightly worked. The range for pasture size is so large due to forage quality, forage type, stage of growth, and the horse’s size and workload (work could include states such as pregnancy or growth). While an adult horse on lush pasture may be able to eat enough grass to meet his energy needs for maintenance or even light work, you need to take many things into consideration. Are you feeding anything else in addition to pasture, such as grain or supplements of any type? Is your horse stabled for any significant period of time (more than 4 hours a day)? How many horses/acre do you have? What other plants are in your pasture (including trees)? You’ll want to check for poisonous varieties and remove those.

How can I tell if my pasture is providing adequate nutrition?

The best way to determine pasture quality is to collect and take samples to your local extension office (or to whomever they recommend if your local office does not process samples). They will give you a nutritional analysis of your samples for a fee. You can also check out the The National Forage Testing Association for listings certified forage testing labs. If you mix your own grain, you may also want to have samples analyzed.

. Another method of determining approximate quality of feedstuffs is to obtain book values from a resource such as the Horse NRC (National Research Council’s Nutrient Requirements of Horses (NRC, 1989)). However, this is just PART of the equation, you must also balance your ration! Many types of software are available to help you balance your ration. I like the old Pegasus software, but you can also make your own spreadsheet in Excel, or use one of the many other resources available. Ask your vet or equine extension associate if you need assistance.

What are some basic guidelines for feeding in the summer when my horse is on good pasture?

First and foremost, always provide plenty of fresh, clean water for your horses. Water consumption can increase dramatically as the heat soars, especially if you do not have shade available. An inactive horse can easily consume 10 gallons of water per day, while an active horse can consume much, much more.

Always be sure to provide plenty of high quality (nutrient dense) forage in the form of pasture or hay or a combination of the two. It is generally recommended that most horses receive 1.5-2.0% of their total body weight in forages per day (for maintenance - work increases nutrient needs).  In other words, a 1000 lb horse needs access to 15-20 lbs of forage per day to eat. That does not include wastage, which inevitable, especially when a horse is on pasture. A general rule of thumb for horses on pasture (that are not receiving additional supplementation) is to ensure that they have access to 3% of their body weight (30 lbs of forage a day for a 1000 lb horse - how much pasture area this is equivalent to depends grass type and density and can increase if your pasture has too many horses).  

Provide adequate minerals, as most pastures and forages are deficient in some minerals. Selenium is deficient in many eastern pastures, and too high in other areas of the country. Sodium chloride is generally deficient in forages, so provision of a salt block is generally recommended for all horses. Some people prefer to feed mineral blocks, but I personally prefer plain salt blocks. Some horses will overindulge in flavored mineral blocks, especially, which can lead to problems including colic or intestinal blockage.

Also, use common sense and keep an eye on your horse’s body condition. If he seems to be getting a bit thin, if your pastures aren’t very productive, or your horse seems hungry and starts chewing trees, fences, etc. out of more than boredom, try supplementing some high quality forage and grain if necessary.