Growth Cycles of Pasture Grasses

Kelly Vineyard explains how to manage the dietary requirements of dressage horses continuously turned out.

Q: I’m a competitive lower-level rider, getting ready to go to the championships. I keep my horse out on field board and have noticed that the grass isn’t as rich now as it was earlier in the season. What adjustments should I make to his daily ration to ensure that he doesn’t drop weight?

Name withheld by request

Kelly Vineyard, MS, PhD

A: Keeping horses outside and maximizing pasture access has benefits. I am always happy to see dressage riders who are willing to adopt this management strategy.

The foundation of any good feeding program is forage, and it is important to understand the seasonal fluctuations in pasture quality so you can adjust your feeding program accordingly. The growth cycle of any pasture-grass species is dependent on geographical location, light–dark hours (photoperiod) and air temperature. Pasture grasses are classified into two categories based on whether the period of highest growth rate is during the cool portion of the growing season (cool-season grasses) or during the warmer days (warm-season grasses). Identifying which type of grass is growing in your horse’s field will help determine the right time to begin supplementing with hay, which is when a significant decline in pasture growth rate occurs.

During the active growing season, good-quality pasture serves as an excellent source of calories, protein, fiber and some vitamins and minerals, such as vitamin A, vitamin E and potassium. But when the grass goes dormant, there is less forage available in the pasture and what is there is not as nutrient dense. This means that you will need to supplement the pasture with hay to make sure your horse receives the necessary fiber for proper gut function. A general rule of thumb is that horses should receive 1.5 to 2 percent of their body weight in forage per day to keep the gut functioning properly. If good hay is hard to come by or challenging to feed on pasture, you can utilize a complete feed (a commercial feed with the forage built in) or other forage alternatives, like pelleted hay or beet pulp, to supply necessary fiber. 

The best type of hay to feed depends on several factors, including the horse’s daily caloric requirements, special metabolic needs (for example, low-carb hay) and his individual preference in addition to forage availability. In general, good-quality grass hay works well for horses with a more efficient metabolism—the easy keepers—while a grass/legume-mix hay is best for those with higher caloric requirements or for hard keepers. Feeding supplemental hay will adequately replace the calories, fiber and protein that the pasture can no longer supply. However, compared to pasture, hay contains relatively low levels of vitamin A and vitamin E. Therefore, it is a good idea to review the rest of your feeding program to make sure these requirements are being met by either the concentrate portion of the diet (grain) or by a well-balanced supplement. 

Generally, most dressage horses in training should receive some type of concentrate to complement the forage portion of the diet. At the very least, any horse kept on pasture will need a balanced vitamin/mineral supplement to supply essential nutrients lacking in forage. If your horse has already been receiving a well-fortified concentrate and you are feeding it according to the manufacturer’s directions, then you likely will not need to feed additional supplements. If you have not been feeding anything else in addition to pasture, now is a good time to find a product that meets your horse’s caloric needs and will supply essential nutrients lacking in hay. Ensure that the product you select contains high-quality sources of protein and is well fortified with trace minerals like copper, zinc and selenium as well as vitamins A and E. As your training program intensifies leading up to the championships, you may find that your horse needs additional calories to maintain his body weight. If this is the case, increase the amount of concentrate you are feeding (follow the manufacturer’s directions). If your horse tends to lose weight easily, consider feeding a fat-added concentrate that is more calorie and nutrient dense. This will allow you to feed less volume while still supplying necessary calories and nutrients.

Supplementing good-quality grass or grass/legume hay along with making any needed adjustments to your concentrate-feeding program during times of reduced pasture growth will help to make sure your horse is in top form when the time comes to ride down the centerline. 

Kelly Vineyard, MS, PhD, is a research equine nutritionist with Purina Animal Nutrition, where she develops horse feed products. A dressage competitor, she is a USDF bronze and silver medalist (






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