If your horse’s diet consists primarily of forage, your pasture must meet all his nutritional requirements. Here’s how to ensure he’s getting what he needs from his grazing space.

If you pasture your horses, chances are you’ve done a lot of work planning and planting a nutritious mix of grasses. But there’s a bit more you need to know in order to ensure you’re delivering complete and safe nutrition to your herd.

Two essential nutritional factors

Salt and minerals are two nutritional factors that are often overlooked, but are essential for horse health.

1. Salt

We may think salt blocks are only important during the hottest time of the year to help with water loss. But salt – sodium chloride – is essential to a horse’s nutritional needs all year round, and its presence is often very limited in forages and hay.

“When I do forage tests, it’s not unusual to find calcium levels at 0.3 or 0.6%, but sodium levels can be as low as .005%,” notes Kathleen Crandell, who holds a PhD in equine nutrition and works with Kentucky Equine Research. “This is certainly not sufficient for optimal health.”

If you notice your horse eating dirt, it may be due to its sodium content. Adding a salt block to your pasture, regardless of the time of year, is sound nutritional management.

2. Minerals

In order to maintain health, horses must also ingest an adequate array of minerals in the correct ratios. Calcium, magnesium and phosphorus, plus copper, zinc and selenium, are examples. The first three are critical in bone formation and maintenance, but the entire spectrum of macro and micro minerals impacts other bodily functions. Be sure not to leave them out of your regimen.

The problem is, while calcium is often adequate in grasses, copper and zinc are frequently found in low levels, and it’s not unusual for phosphorus levels to be either too low or too high.

In the event your pastures are imbalanced, providing free choice minerals, perhaps with added salt, is the solution. Steve Jackson, president of Bluegrass Equine Nutrition and an international Thoroughbred consultant for 28 years, notes that horses typically consume two ounces of salt per day – when you know this, you can judge how much mineral content you’ll need in a salt block or free choice salt/mineral supplement.

You can also include magnesium oxide in your mixture since it tends to inhibit horses from over–indulging. However, Dr. Crandell warns against using a cattle block since these are normally low in selenium and copper. Put your money into a block or granulated mineral mixture specific to equines.

And then there’s clover

Some experts do not recommend planting stands of this legume at all. At 35% protein, in some cases, clover is high in sugar and protein, but lower in fiber. Roger Allman, international expert in pasture management and owner of The Farm Clinic, does not consider these characteristics beneficial.

Other experts recommend clover when used sparingly. David Crouch, who manages the pastures at prestigious Denali Stud, likes adding a bit of white clover for its sweetness, especially for his mares in foal. He also appreciates the small boost in protein that white clover provides.

Jackson is also an advocate of white clover, but like Crouch, only in small amounts — say 5%. He agrees it has a high protein count, but adds that it also delivers superior concentrations of digestible energy, vitamin A and calcium. Jackson also appreciates white clover’s added benefit: it can take atmospheric nitrogen and fix it in the soil, which means there’s less need to re-introduce nitrogen into the soil via fertilizer.

The good and bad news about poisonous plants

Though reviews are mixed about clover, everyone agrees that certain other plants should not be present in any pasture. In the central US, for instance, there are plants you must avoid altogether: horse nettle, milkweed, hemp dogbane and black nightshade. That’s the bad news.

The good news is that horses are very good at staying away from poisonous plants. Allman notes they’ll eat everything else down to the soil, but typically leave the poisonous plants alone. He stresses, though, this does not apply to foals, who haven’t yet learned the art of grazing, so be especially vigilant if you have babies in your pasture.

The problem with tall fescue

If you have broodmares, be especially vigilant about tall fescue. This is a staple grass in many parts of the country. A hardy cool-season perennial, it grows well and can have a long production season. But it has also been associated with serious health problems in horses, primarily in reproduction.

Problems can run the gamut from reduced milk production in mares post-delivery, to prolonged gestation or abortion, and foals with depleted immune systems, hyperthyroidism or immature development. These are not the only difficulties associated with tall fescue toxicosis, so you can see how imperative it is to shield broodmares from this plant as a grazing source.

The culprit is a toxin called “ergovaline”. The prevalence of its effects varies regionally, but all parts of the country are affected to one degree or another, with the southern states being most prone to higher levels of impact. While drugs are available to mitigate the adverse effects in mares who must graze on endophyte-infested tall fescue, the best solution is prevention.

There continues to be a push for more varieties of tall fescue that will perform well and not produce toxicosis. You can find research results that support the use of these new varieties, but Dr. Crandell has a warning. She has observed that even if you raze your pasture and plant these seeds (some of which are expensive), the varieties that are not drought-, cold- or hoof-tolerant will die out in about five years, and the original tall fescue can come back. Since it looks like the newer varieties you so painstakingly planted, you won’t know your pasture is again infected.

Is alfalfa getting a bad rap?

Typically you don’t find alfalfa planted in grazing pastures, though it is often used in hay bales for feeding during the winter months, or to meet specific nutritional needs. Most experts don’t include alfalfa in their pasture mix recommendations. Our experts agree; Denali feeds alfalfa hay, and this practice is advocated by Jackson and Dr. Crandell, as well as agronomist Allman.

There are reasons for this, including the fact that alfalfa, a legume, is not as persistent as grasses in a pasture setting. With its bunching growing habit, it can produce bare spots. It also gets very stemmy and “lignified” (a term that refers to indigestible fiber) when overly mature. And come the first frost, alfalfa goes dormant.

Alfalfa is also reported to be the source of many health problems, including weight gain and orthopedic problems. Whether or not this is true is up for debate, but what we do know is that alfalfa is quite high in protein, coming in at an average of 18%. It’s also high in calcium, sugars and digestible fiber along with a small amount of fat. It exceeds the protein needs of horses at most stages of life, so be smart about how you use it.

For adult horses, alfalfa is quite valuable as hay (see sidebar) since it provides needed nutrition and calories to combat extreme weather. Often mixed with orchard or Timothy grass, alfalfa is most prevalently used as hay. If you are purchasing hay rather than harvesting it, you can buy alfalfa or Timothy separately and combine them as you feed.

All in all, understanding the individual characteristics of different forages, as well as your horse’s nutritional needs, allows you to make wise choices. Troubleshooting your pasture and assessing the nutritional needs of each horse is a sort of partnership, and with a bit of research, you can optimize both the space you have for pasture, and the health of your horses.