| ||Introduction | Behavior associated with food consumption | Preference of forages by horses | Forage digestibility | General forage feeding guidelines | Summary | References | About the Author
Horses ... first there was the eohippus and at only 12 inches tall, he fed on leaves, soft grasses and ran from his greatest predator, the saber tooth tiger. As evolution of the horse progressed through the stages of the Mesohippus, Merychippus, and Pliohippus to today's Equus, the horse remained a forager. It is no wonder that nutritionists consider forages to be the FIRST step in establishing a sound diet for the horse. Even today, one cannot dispute the wisdom of Columella, A.D.50 who stated, "For those whose pleasure it is to rear horses it is of the utmost importance to provide a painstaking overseer and plenty of fodder."
Thousands of years of foraging has resulted in a rather unique digestive system that bears resemblance to only the rabbit and guinea pig. Placement of a rather small stomach immediately prior to the small intestines where most of the starch, fat, and protein digestion occurs in the horse very much like other monogastric animals. But just beyond the small intestines is the cecum, a blind gut compartment that harbors the microbial flora similar to the microbial population in the rumen of cattle. The well developed cecum is the site of fiber digestion and is responsible for the horse classification as a non-non-ruminant herbivore.
Horses are best able to digest higher quality forages when compared to ruminants. As in the rumen, fiber is broken down by microbes and converted to the volatile fatty acids (VFA's) acetic, propionic, and butyric acids which can be utilized by the horse for energy. These energy sources do not represent the concentration of energy such as glucose, but nevertheless, are very important to the horse, furnishing approximately 30% of the digestible energy intake. For a more in depth look at forage utilization by the horse, grazing patterns, preferences, digestibility values, and definite reasons to consider forages the first step in the balancing the diet for horses will be discussed.
Behavior Associated With Food Consumption
Grazing clocks and extended observation watches have been utilized by researchers to determine what a horse does during the day. The relatively small stomach and energy needs of a large horse necessitates extended grazing periods. In a pasture grazing situation with forage readily available, horses grazed approximately 72% of a 24 period. In a similar study of horses grazing bermudagrass pasture, horses grazed 67% of the 24 hour period, but when grazing lush ryegrass, only 57% of the 24 hour period was utilized for grazing. Presumably, enhanced bite size of the forage decreased grazing time of ryegrass. It is interesting to note that feral horses also spend approximately 75% of their time grazing forages. It has been estimated that a horse will consume between 2.0 and 2.5% of their body weight in forages during a 24 hour period.
From the above data, one may conclude that horses tend to be more continuous consumers of forage than ruminants. Yet stalled horses are usually fed twice during a 24 hour period. Consumption time for stalled horses has been reported to represent approximately 13 to 15% of a 24 hour period, depending on the amount of grain vs. hay. Horses fed only concentrates were 6 times more likely to chew wood and 2.5 times more likely to eat their feces.
A subsequent study established a direct correlation between length of consumption time and wood chewing. The less time a horse spent eating, the more likely the horse was to chew wood. It is true that pelleted forages may ease a storage or availability problem associated with fresh forages. Yet, horse owners should be aware of the potential negative side effects such as wood chewing and coprophagy when horses are not fed long stem hay or grazed. Wood chewing has not been strongly associated with feeding cubed forages.
Preference of Forages by Horses
Horses are notoriously selective grazers. Little documentation has established why certain areas are selectively grazed while other areas are ungrazed or become dunging areas. A pasture study in Texas reported a repeated tendency for horses to always graze the fence line of an enclosure and various areas that represented between approximately 38% of the available acreage. This grazing area percent would vary with the number of horses and forage availability (increasing as forage became more limited).
Since young, growing forages tend to be higher in digestible nutrients, it is reasonable to assume that the equine grazer repeatedly grazes the same areas to obtain more tender and less fibrous forage. A study in Texas reported a 3% difference in Tift 44 crude protein between grazed vs. ungrazed areas.
Climatic variations result in disparity among preferred forages by horses. A report from New Zealand indicated that horses favored prairie grass (Bromus willdenowii), followed by Italian ryegrass, white clover, and timothy. A creeping red fescue was favored by horses in Suffolk, England over creeping red fescue Canadian variety, crested dogstail, cocksfoot, and perennial ryegrass. In the southern United States where winter annuals are well suited to the mild climates, horse preferred annual ryegrass over oats and wheat. The winter annual preference was particularly evident later in the growing season, even though the forages were maintained in the vegetative state. Rye and triticale were avoided by yearlings in this research. A second cafeteria study demonstrated crimson, Berseem, and Subterranean clovers were equally preferred while yearlings avoided arrowleaf clover. Tannin is a chemical in arrowleaf clover which deters consumption.
Fewer studies have addressed the preference of the horse for various hay varieties. In response to local questions about acceptability of the improved Bermudagrass varieties, research at Georgia was conducted to evaluate five bermudagrass varieties and establish any correlations with the physical form of the plant. Coastal bermudagrass was clearly preferred by all horses, followed by Tifton 44 and Tifton 78. Tifton 85 was a distant fourth while horses basically refused to eat the coastcross bermudagrass hay. Morphologically, the Coastal bermudagrass hay had the smallest stem diameter, leafblade width and length, and lowest neutral detergent fiber (NDF), a lab analysis value that indicates the potential energy content, filling effect, and intake of a forage. The lower the NDF percent, the greater the energy value and digestibility of a feed. Despite relatively equal crude protein levels among all hays, the least preferred hays (Tifton 85 and Coastcross) had the widest leaf blade and highest NDF values.
Is a horse's preference for various forage varieties an important management question? In many cases, basic acceptability of a forage seems "good enough", as long as the horse is in acceptable body condition. But within the "accepted" forage varieties, can preference impact growth and body condition significantly? Future research should be directed toward establishing a greater understanding of the horse's selectivity for forages to maximize growth and forage utilization.
As horse owners, many of us know how much we feed, either by volume or weight. Weight is a more accurate assessment of feeds than volume; all horse owners are encouraged to feed by weight, not volume. If horses are stalled, owners also are quite aware of manure production. Nutrient disappearance between the amount consumed and amount excreted is indicative of the digestibility of a feedstuff. Forage utilization in the horse is not thoroughly documented, but much of the available data has been summarized in Table 1. Standards of evaluation include the percent dry matter (includes all nutrients of a feed, digestible and indigestible), crude protein (based on nitrogen content of the feed which is largely available to the horse in most horse feeds), digestible energy (the best indicator of feed quality; energy is the main nutrient required by the horse), and neutral detergent fiber (an indicator of fiber digestibility; lower numbers are desired). Readers should note different methods of feeding and collection, forage preparation, forage maturity, and types of horses fed prevent direct comparisons between most varieties, but the values do provide a perspective of forage digestibility.
Only one study reported digestibility of grazed forages. Orchardgrass and fescue pastures had two of the highest dry matter and crude protein values in Table 1. While methodologies may be responsible for some of the difference between hays, the higher digestibility values are perhaps more reflective of horses' selectivity for more digestible forages. The whole plant is cut for hay and horses cannot be as selective of plant structures when consuming hay.
Six grass hays listed in Table 1 indicate that dry matter digestibility ranges from 41 to 58% with an average of approximately 50%. Crude protein digestibility was most often in the low 60% range while digestible energy tended to average in the upper 40 percentile.
Of three forms of alfalfa fed, dry matter digestibility was similar to grass hays, yet crude protein and energy digestibility values were greater than values reported for grass hays. Based upon the National Research Council's report on forages, alfalfa averages 2.24 Mcal/kg while most grass hays average 1.5 to 1.9 Mcal/kg. Considering the higher initial nutrient content along with the elevated digestibility values for crude protein and energy in alfalfa, horse owners should realize that less actual weight of alfalfa hay (compared to grass hays) may satisfy or exceed the horse's nutrient requirements. Alfalfa is known as the "Queen of Forages" and it truly is a valued forage in many equine establishments.
An interesting study of a Canadian product, Alfamaize, showed promising feed digestibility values when compared to a 65% concentrate, 35% bermudagrass hay diet to exercising horses (Table 1).
Table 1. Digestibility values (%) for various forages fed to horses.
43 – 64
52 – 68
44 – 57
39 – 52
43 – 64
36 – 49
41 – 56
41 – 53
44 – 57
36 – 54
52 – 60
67 – 75
|65% concentrate with 35% Bermudagrass|
|NR = not reported|
General Forage Feeding Guidelines
Horses are expected to consume 2.0 to 2.5% of their body weight in feed every day. Horse owners must recognize individual differences among horses and understand how stage of production and exercise influence nutrient requirements. Young horses do not have the physical capacity to consume enough hay to meet their energy requirements. Hay is not as energy dense as grain which is usually needed in the diet to meet energy requirements of a young growing horse. Lactating mares and exercising horses also need a more concentrated source of energy than most forages can provide. But for every horse, at least 1% of the horse's body weight should be provided daily in some type of forage. An appropriate starting point for mature horses is to evaluate the body condition. If adequate body condition is apparent, the horse might do well on a total forage diet at the level of ~2% of the body weight. If more body condition is desired or the horse is going to be working above maintenance requirements, 1.5% to 1.75% of the body weight might be offered in hay along with .5% to .75% of the body weight in grain (any change in diet should be made gradually). Since alfalfa may run 15% to 20% higher in energy and is more digestible, a slightly smaller portion of alfalfa hay than grass hay may be needed, particularly for a mature horse at maintenance.
Selecting quality hay can be difficult because there are rarely feed tags to guarantee the nutrient content of the roughage. That doesn't mean owners CANT determine the nutrient content of hay, it simply means owners usually must rely on their visual appraisal of hay to perceive quality.
Factors that affect quality include:
1. Plant maturity. The older a plant at cutting, the more fibrous the hay will be and the LESS digestible the hay will be for the horse. Higher quality hays will be (a) softer to the touch because the stems are less fibrous, (b) leafy which enhances softness of the hay; leaves are the most digestible components of a plant; and (c) seed heads should not be predominant.
2. Color. Green color indicates the hay was cured properly and free of rain. Green hay is associated with carotene, the precursor to vitamin A, and insures vitamin A will be in ample supply for the horse.
3. Aroma. Some hays may smell better than others, but no hay fed to horses should smell musty or be excessively dusty. Dusty, moldy hay may initiate a respiratory condition called heaves that is not readily curable (new treatments are being developed with some success).
4. Free of weeds and foreign materials.
5. Hay variety. Plant species differ widely in nutrient content and consequently, so will the hay. KNOW THE SPECIES AND THEIR AVERAGE NUTRIENT CONTENT!
After deciding upon the variety to be fed, the most important factor to determine digestibility for the horse is maturity. Crude protein and energy of a plant is highest when the plant is young but decreases with age. If hay is harvested even a couple of weeks past the peak stage, hay quality can suffer significantly. More fibrous, mature hays also may be associated with a higher incidence of colic, especially impaction colic. Therefore, horse owners should place more confidence in hay producers that have their hay tested regularly . . . it can make a difference! Does it pay to test horse hay? Consider the examples below and decide for yourself.
1. Alfalfa averages $90.00/ton and 18.2% crude protein in Canada. The cost would be $0.24/pound of protein. (2000 lb. x .182 = 364# protein. $90 divided by 364 = .24) On a cost per pound of hay, alfalfa costs $0.45/pound. What if the alfalfa was only 15% CP and the cost was the same? The cost/pound of protein would be $0.30/pound.
2. Timothy averages $75.00/ton and 8.2% crude protein in Canada. The cost would be %0.46/pound of protein. On a cost per pound of hay, timothy costs $0.375.
3. Just for comparison, what does protein from barley cost? At $3.60/bushel which weighs ~48 lbs. and averages 11.5% crude protein, the cost is $0.65/pound protein from barley.
Consider all the factors for the best economical decision relative to the nutrient needs of horses being fed.
Horse owners should understand that the horse has evolved and survived because of its ability to seek and digest forages. Therefore, it is only natural for horse owners to consider the quality and quantity of forages FIRST when deciding how to meet the nutrient needs their horses. The best managers know the nutrient content of the forage, maximize its use, and feed concentrates only to meet requirements not met by the forage. "Putting forages first" on your list to understand and utilize efficiently should help insure a very successful equine feeding program.
1. Moffitt et al., Virginia, Equine Nut. Physiol. Symp. 1987.
2. Aiken et al., Texas, Equine Nut. Physiol. Symp. 1987.
3. McCann et al., Georgia, Equine Nut Physiol. Symp. 1995.
4. Vander Noot et al., New Jersey, J. Anim. Sci. 31:351, 1970.
5. Redmond et al., South Carolina, J. Eq. Vet. Sci. 11:215, 1991.
6. Harbors et al., Kansas, J. Anim. Sci 53:1671, 1981.
7. Haenlein et al., Delaware, J. Anim. Sci. 25:740, 1966.
8. Younglove et al., Texas, J. Eq. Vet. Sci. 14:599, 1994.
[back to table]
About the Author
Dr. McCann, Associate Professor, Animal and Dairy Science Department, University of Georgia, has done extensive research on preference and utilization of forage by horses including palatability and digestibility. She works closely with horse owners to develop horse rations that optimize forage utilization.
This article was presented at, and appears in the Proceedings of, the 1996 Alberta Horse Breeders and Owners Conference.