Rusty's been your faithful companion for many years, and he never seemed to show any signs of getting older...until this past winter, that is. One morning, you looked at him and noticed that he had dropped some weight, and that he didn't demonstrate his usual enthusiasm for his breakfast. What grain he did sample, he tended to dribble out of the corners of his mouth, largely unchewed. Gradually, hay began to present a problem as well, and your old friend struggled to grind the fibrous forage. Although otherwise he seemed fine--he wasn't lame, didn't run a fever or look depressed, and greeted you with the same calm equanimity he'd always shown--his weight loss started to concern you. How could you help your 20-something equine get more value from his food and regain his former round physique?
Be willing to experiment to see what your older horse likes, and what he finds easy to eat.
Getting The Most From Feed
It's been stated that the best feed in the world will do a horse no good if he can't digest it. So what's stopping the older horse from extracting nutrients from his diet? Let's start at the mouth, and work back.
Foremost on the list of suspects is the inevitable decline of the older horse's dental health. As a horse ages, he gradually wears down the grinding surfaces of his teeth--and while the teeth continue to grow throughout his life, often the wear and tear teeth receive outstrip the replacement rate. In addition, his incisors (vital to tearing off grass and forage from the ground) become more sloping over the years, and as they verge on the horizontal, they become far less efficient at biting down and tearing fibrous foodstuffs.
Dental "hooks" on the molars, a problem for all domestic horses throughout their lives, can compound the problem (and are especially likely if your horse has not had the benefit of routine--and thorough--"floating" or rasping of his teeth as he aged). Older horses also can suffer from broken or missing teeth, usually as the result of trauma (although long-term infections of teeth also occur and can have the same result). A broken tooth is not only painful, it can interrupt the normal dental surfaces and make it next to impossible for your horse to chew. The loss of a molar or premolar also can reduce the ability of the horse to chew his feed--and if a molar or premolar is lost, the opposing teeth will grow into the space, creating a condition called "wave mouth, which further complicates matters.
If an incisor or incisors are lost, your horse might not be able to graze efficiently--so don't depend on pasture to help maintain his condition. There always is the possibility of dental abscesses, often caused by a particle of food, or a foreign object picked up while grazing, lodged in the gum.
All of these dental problems can lead to a loss of appetite (after all, who wants to eat when your mouth hurts?) or poorly chewed food that might fall out of your horse's mouth in "quids." The food that does get swallowed often is harder to digest because it is in larger-than-normal chunks that the body might not be able to break down. In very old horses, the teeth can become so worn that they are practically nonexistent; without the essential grinding surfaces, such a horse has no way of taking in forage or grain in the normal way.
Fortunately, there are dietary solutions, approaches that we'll discuss later in this article. Needless to say, the older horse's teeth should be checked at least twice a year, and floated as necessary. Your veterinarian should pay special attention to the molars at the very back of the jaw, where hooks and points often get neglected.
An older horse's metabolism often is somewhat slower than a young horse's, and his more modest energy expenditure should mean that his baseline requirement for calories is lower than it was in his early years. Unfortunately, there are other factors at work that cancel out this effect. Studies have demonstrated that the geriatric horse (usually defined as 20 years or older) suffers from decreased digestive efficiency--his gastrointestinal tract becomes less able to process and extract the nutrients from his feed, so many essential dietary ingredients fail to be absorbed and instead pass through the body untouched. The ability to digest fiber is decreased, and studies in other monogastric (one-stomached) animals suggest that horses probably experience a decrease in stomach acid and enzymes as well as decreased motility of the intestinal tract.
Research on horses indicates that the absorption of protein (essential for the repair of bones and soft tissues) and phosphorus (involved in the strength and resilience of bone, as well as a number of maintenance functions at the cellular level) is compromised in older horses, and that as a result, the requirement for both these minerals is increased as a horse gets older. (The decreased protein absorption actually is the result of decreased retention of nitrogen.) Calcium absorption does not appear to be affected, but if you increase the amount of phosphorus in the diet, it's a good idea to increase the amount of calcium in order to maintain that all-important calcium:phosphorus ratio of 1:1 or better. (Fortunately, horses seem to tolerate high levels of calcium very well.) Starch digestion is another area that appears not to be affected by age.
Sarah Ralston, VMD, PhD, ACVN, of the Department of Animal Science at Rutgers University in New Jersey, has done extensive research on the nutritional needs of geriatric horses. She notes that the results of studies performed to detect decreased digestive efficiency in older horses might be, in part, an indicator of what happens to a horse which suffers years of chronic parasite infestation. She explains that the first research in this area was done in the early 1980s, using mares in their 20s which through much of their early lives did not have the benefit of advanced deworming drugs such as ivermectin. Today's older horses, which most likely have had the benefit of better deworming programs throughout their lives, are less likely to show extensive parasite damage in the intestinal tract, and therefore might be able to derive more benefit from their diets, for more years, than those research mares foaled in the 1960s.
Still, it's fairly clear that the ability to digest fiber is compromised in almost all older horses--and since fiber should make up at least 50% of the overall diet by weight, it's a significant problem. Researchers suspect that the difficulty is two-fold: first, many older horses find it hard to chew forage properly, especially when it is fibrous, long-stem hay instead of sweet, young grass; and second, a less-varied and less-efficient population of microorganisms in the colon might make for a less-thorough job of fiber fermentation and nutrient extraction.
The ability to manufacture or absorb certain vitamins also seems to decrease as horses age. Ralston suspects that the decrease of gut microflora compromises the ability of the horse to manufacture his own B vitamins (normally produced in abundance) as well as vitamin C (ascorbic acid), which is important for the horse's immune function. A healthy horse manufactures sufficient quantities of his own vitamin C, but many older horses which suffer from pituitary dysfunction (a common result of the aging process) show low blood levels of C, which might make them vulnerable to viral infections. Some researchers suggest the supplementation of vitamin C to the tune of 5 to 10 grams a day (best obtained in a human pharmacy).
A 1989 study by Ralston and her colleagues indicated that more than 70% of horses over the age of 20 had at least subclinical signs of pituitary or thyroid tumors. (See our cover story for a more complete discussion of these problems.) From a feeding point of view, the most significant thing about these tumors is that they can alter a horse's utilization of glucose, producing glucose intolerance and a decreased sensitivity to insulin--a hormone that helps balance sugar levels in the blood. When blood levels of glucose and insulin become abnormally high in these horses (as they might after the horse has consumed a grain meal), the result often is increased thirst and urination.
Geriatric horses also can suffer from decreased kidney and/or liver function, both of which can have an effect on nutrient utilization. Horses are unique in that they excrete excess dietary calcium in their urine, not in their manure as most other species do--so if kidney function becomes impaired, stones of calcium oxalate can build up in the kidney or bladder. There also is the potential for calcium to build up to dangerous levels in the bloodstream. Horses with kidney failure need to be placed on a low calcium diet (less than 0.45% of the overall ration), and protein and phosphorus also should be reduced (to less than 10%, and less than 0.3%, respectively), contrary to the usual recommendations for older horses.
Horses with liver failure might suffer from jaundice, weight loss, lethargy, loss of appetite, and an intolerance for fat and protein in the diet. Severely affected horses also could be irritable and circle aimlessly, or press their heads against objects. In contrast to kidney failure, horses with liver problems need increased sugar in their diets in order to maintain blood glucose levels; their diets should emphasize carbohydrates and de-emphasize protein and fats. Because the liver also is a site of the synthesis of B vitamins (especially niacin) and vitamin C, affected horses should be fed a diet supplemented with oral B complex (about 5 cc a day) and ascorbic acid.
Finally, there are a number of psychological factors that can contribute to a senior horse's weight loss or lack or condition. First, older equines are, as a rule, less aggressive--so if they are fed in a group situation with younger horses, they might be pushed aside and be unable to eat all they should. Second, they tend to suffer more than younger horses from stress factors. Hard work, being shipped for long distances, or just being chased around the field by a more exuberant pasture buddy can take a toll on the aging horse and cause him to lose his appetite (a condition clinically called anorexia). In general, it takes less to make an older horse lose his enthusiasm for his meals; even water that is too cold (causing tooth pain) might be enough.
Extremes of weather can be particularly hard for geriatric horses. Because they thermoregulate poorly in their golden years, they require more food energy in order to maintain their internal temperatures in bitter winter conditions. Ralston recommends that in cold weather, horses on the high side of 20 years be fed about 120% of the National Research Council's recommendations for daily intake.
"Some horses need even more than this," she says. "I've found some can go up to about 133% of NRC."
This means that in some instances, you might have to exceed 3.0% of your horse's daily body weight per day in feed to help him maintain his condition in winter. Blanketing him warmly, and providing a good windbreak or shelter in his pasture also will help. In hot, humid conditions, horses also might lose their appetites, so if necessary, body-clip your octogenarian and consider giving him a cooling mist with the hose when he is looking particularly uncomfortable. Some farms in southern climates even rig up irrigation hoses on fence lines that spray cool water on the herd several times a day.
Many stress factors can be reduced with some basic management changes, such as putting your older horse in a pasture with others of a similar age, rather than rambunctious youngsters. When you feed him, isolate him in a separate paddock or stall, so that he doesn't have to compete for his meals. Making every effort to keep his appetite good is crucial, because once an older horse gets skinny, it can be a real struggle to put weight back on him.
There are three primary considerations when you design a diet for your older horse--ease of chewing, improved digestibility of nutrients, and increased palatability.
As your horse's ability to chew and digest fibrous, stemmy hay declines, it's increasingly important to provide him with good-quality pasture (just because it's green doesn't mean it's of good quality--many pastures are largely indigestible weeds!). You also need to provide more easily chewed and digested forms of fiber. Instead of stemmy, mature, 100% grass hay, opt for a higher-quality, softer, and less mature mixed hay with a fairly high legume content (up to 60% or so). Your aging equine will find it much easier to chew.
As a test, grab a handful of the hay and squeeze hard--if the hay hurts your hand, it's likely too tough and fibrous for your old guy. For most older horses, it's still a good idea to avoid straight alfalfa hay--while soft and very palatable, it has an excessively high protein content (up to 25% or so) and is very low in phosphorus. (If your horse has a liver or kidney dysfunction, it's particularly important to avoid high-protein legume hays; instead, choose a grass hay that is immature and thus still fairly soft.)
There might come a day when even high-quality, soft hay is too much of a chore for your older equine. In this case, you might have to do some of the chewing for him, so to speak. Chopped hay is a good start--you can chop it yourself, or buy it already chopped in bagged form. Or you might want to consider one of the great variety of hay cubes or pellets available. Because these tend to be rather hard in texture, it's useful to soak them in warm water for an hour or two before feeding, to make a gruel or a soup. The worse the condition of your horse's teeth, the more crucial this step is. Chopped, cubed, or hard pelleted fiber products might increase the risk of choke in older horses when they are fed dry and are incompletely chewed. You also can try looking for a softer pellet, and slowing your horse's feed consumption by putting a few large, smooth rocks in his feed tub.
Beet pulp is still another excellent fiber source for older horses--once soaked, it's soft and very easily chewed (suitable for even the most toothless geriatric), extremely digestible, and a good source of calcium.
What about grain? The decreased efficiency of the digestive tract means that most horses will need the help of a little grain to help maintain their condition in their senior years--and a commercial pelleted or extruded ration is usually a better idea than unprocessed whole grains (which are difficult to chew). Pelleted and extruded rations are made with finely ground grains, so in a sense they are "pre-chewed." They also are exposed to heat, which makes some nutrients more available and easier to absorb. Pelleted feeds, in particular, are easy to soak in water so that a toothless horse can consume the resulting mush. (Soaking grain rations in two or more gallons of warm water is an especially good idea in the winter months--it will make the feed more palatable and at the same time increase your horse's water intake.)
The nutritional needs of an aging horse are in many ways similar to those of a weanling, especially in terms of protein levels and calcium and phosphorus. So, feeds designed for young horses might be a good choice, as are those formulated especially for older horses. "Senior" feeds often are manufactured with a softer-textured pellet format, which improves their palatability. They are justifiably popular with many owners and their horses.
Look for a grain ration that provides about 12-14% crude protein (a little higher than the level recommended for younger, mature horses), 0.3% phosphorus, and a calcium level of at least 0.3% but not more than 1.0%, on a dry matter basis. (Although it's controversial, there is some indication that an extremely high calcium level in the diet might exacerbate arthritic changes in an older horse's joints, leading to increased calcium deposition.)
Feeds with added fat also are an excellent choice for older horses, except for those with liver dysfunction. Fat, in the form of vegetable oils or rice bran, is extremely digestible and can help immeasurably in the task of keeping an older horse's ribs covered, since it contains almost 2 1/2 times more energy, pound for pound, than carbohydrates. Adding fat is an excellent way to increase the calorie density of your horse's diet without increasing its volume by more than a few ounces.
You can top-dress vegetable oil to a level of up to two cups per day (spread over several meals a day), or choose to buy a feed that is formulated with extra fats (look for a feed tag that lists a crude fat level of at least 5%, and preferably up to 8%). If you feed rice bran, look for a brand that is calcium-supplemented; this will help compensate for its unusually high phosphorus content.
Depending on the protein content and quality of your hay, you might find that you have to supplement protein in the diet of your older horse. Soybean meal probably is the best way to do this, according to Ralston. It provides an excellent quality of protein (with a good amino acid profile) and needs to be fed only in small quantities. Ask your feed company's equine expert, or your local agricultural extension agent, to help you determine how much of the supplement to feed in order to balance your particular horse's diet. For most horses, a quarter- to a half-pound of soybean meal is appropriate; resist the temptation to overdo it.
"Complete" feeds, designed to provide concentrates and fiber, are another good way to feed the older horse which finds it difficult to eat hay. Look for those with a high beet pulp content and energy level (such as Respond, a feed designed for racehorses with respiratory problems). Pelleted complete feeds also can be soaked. Arrive at a gruel consistency by adding about a half-gallon of warm water per pound of feed.
In terms of feed supplements, Brewer's yeast is a good choice for many aging equines because it fulfills a double function--not only does it seem to improve feed utilization (by encouraging the health of the gut microflora), but it also is an excellent source of B vitamins, which are a concern particularly for horses with pituitary tumors (Cushing's disease) and liver disease. And as we mentioned earlier, it might be worth adding some vitamin C to your horse's diet, particularly if your horse shows signs of a compromised immune system (which Ralston says can even include an increase in the incidence of surface problems such as rainrot or thrush). Vitamin C is a water-soluble vitamin, so any excess is excreted easily by the body. You might want to consider one of the digestive-aid or probiotic supplements available.
If your horse suffers from liver failure, you'll need to provide him with a high-carbohydrate diet, based on processed (not whole) corn or milo, or a low-protein sweet feed or pellet, as well as low-protein grass hay and/or beet pulp. Because a dysfunctioning liver doesn't release B or C vitamins as it should, you also should supplement those two nutrients.
In the case of kidney failure, avoid feeding legume hays (such as alfalfa or clover), wheat bran, or beet pulp (legumes and beet pulp for their high calcium content, and bran for its high phosphorus). Focus on grass hay and cracked corn, or a complete pelleted ration with less than 10% protein.
Be willing to experiment to find out what your older horse likes, and what he finds easy to eat. A finicky appetite comes with the territory. And of course, make sure your horse always has access to unlimited amounts of fresh water, since no dehydrated horse maintains a good appetite. In the winter, warming the water has been shown to increase water intake dramatically, which is never a bad thing. Cater to his dwindling interest in food by offering small meals, more often. With a little extra TLC on the nutritional front, most geriatric horses, even the relatively toothless, can continue to lead healthy and productive lives for many years.
About the Author
Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.
POLL: Visits from the Vet