EQUINE CARE—BY HEATHER SMITH THOMAS

By Heather Smith Thomas Careof

Keeping weanlings and yearlings in optimum health and growing properly is the goal of every breeder. Stephen Duren, PhD (equine nutritionist, Performance Horse Nutrition) says it’s important to feed for optimum growth but not push young horses so much with overfeeding that they are at risk for joint damage and skeletal problems.

Many thoroughbred breeding farms in the U.S., Europe, Australia and Japan weigh their foals periodically to monitor growth.

“There are established growth curves for thoroughbred horses and these curves are also based on the country they are in,” Duren said.

“The data has been modified somewhat for each country, to better reflect their situations, and they have established normal growth curves for foals. The word normal is misleading, however, in that not all foals are going to be the same height,” Duren says Genetics will play a role in the individual growth rate. Some farms measure and weigh their foals but there is no growth curve for withers height in the NRC recommendations. Not much research has looked at growth patterns in terms of withers height, but these types of measurements are built into certain monitoring programs. “Many of my clients monthly weigh all foals, weanlings and yearlings on the farm, and track that—not only by how a particular foal is doing and how the rest of the farm’s foals are doing but they can also compare that to a central Kentucky average growth rate, or a Canadian average,” Duren said. This can be a way to compare an individual foal with other foals on the farm, and how they all compare to breed average. “My caution with this

tool is that we don’t want to utilize just that number to determine how to feed the foal,” he says.

“The other important thing about a foal growth curve is the shape of the curve and not necessarily the height of the curve. There will always be some young horses taller or smaller than average, so the shape of that curve is what’s important. It should be a smooth, consistent growth curve with no erratic deviations [such as growth spurts or periods of decreased growth rate] that might create problems,” Duren explains.

If weanlings going into their yearling year were not adequately fed through winter their growth curve tends to flatten out.

“Then when lush pasture becomes available they rebound with rapid growth. I advise breeders to be aggressive enough with feed in winter to keep the growth curve going smoothly,” he says.

He advises them to anticipate what will happen with growth rate when these youngsters go out on green grass in the spring.

Weaning is another time in the foal’s life when there can be a glitch in growth rate; the foal may not eat as much for a while during the stress of weaning, and then show a rebound in growth after he adjusts to being weaned and is eating better again.

“We have to anticipate these growth rate changes and make feeding adjustments before they happen. For instance, as we move into green grass in central Kentucky, a filly that is very robust—with a tendency to become overweight—may need to have her feed reduced before that point so that she doesn’t become overweight. A person needs to anticipate what could happen, rather than be reactionary after it happens,” he says.

It takes fine-tuning as you go along. “This is where monitoring body weight of the growing young horse is a good tool, but can’t be the only tool. We need to keep looking at body condition, anticipating what will happen next, because even looking at the numbers [weight, height] you may miss the trend in a certain individual and get behind. Then your feeding adjustments are reactionary instead of ahead of the glitches,” Duren says.

Feeding young horses is an art and a science.

“Many successful thoroughbred nurseries have staff and management that can objectively look at a horse, with experience to know if something isn’t quite right,” he says.

Brian Nielsen, PhD (Professor of exercise physiology and nutrition, Michigan State University) says many horse breeders tend to breed for big horses because those often sell better than smaller ones. Racehorses come in many sizes, however. Even though a small, wiry, athletic horse may sometimes be a better runner than a larger, taller, longer-striding horse, people still want to buy the larger yearlings at a yearling sale.

Most horses eventually reach their genetic potential, but the wellfed youngster may grow faster at first (and be bigger at earlier age) than the underfed young horse. Thus many breeders want the most growth they can get in their foals and yearlings, so they will look good at sales and also be more ready to start training at a young age. The important thing, however, for the young equine athlete, is optimal growth rather than maximum growth. Pushing young horses too fast may damage growing bones, with too much weight on an immature skeleton. If we aren’t careful in feeding and in monitoring growth rate, we may also contribute to growth spurts that are detrimental to long-term bone strength and soundness.

“People want big horses, so it’s important to feed the young horse properly to optimize growth, without going overboard and causing problems. Big is not everything, but most buyers want them big,” Nielsen said. So if you are breeding and feeding from a marketability standpoint, you definitely don’t want to underfeed these youngsters.

“The 1989 NRC recommendations gave an option so you could target your goal and choose between two growth rates. You could feed young horses for either fast growth rate or moderate growth rate. The idea was that if you feed a balanced diet, both groups (with similar genetic potential for growth) would still eventually all reach the same mature height. It would just take the moderate group a little longer,” he said.

“Most people are cautious when they read about feeding for fast growth rate, due to concerns about developmental problems. You can, however, feed for fast growth without causing skeletal problems, but it is a trickier challenge. Many people do not have a good enough handle on their nutrition [knowing exactly what is in the feed] to avoid problems. When we did the update [2007 Horse NRC] we removed the growth rate discussion, because of the negative association about feeding for fast growth,” Nielsen said.

“When feeding horses we need to look at the nutrient-to-calorie ratio—the calories the horse is receiving, compared to total amount of nutrients. We tend to focus on the big factors such as protein [especially when talking about amino acids such as lysine] and some of the major minerals such as calcium and phosphorus,” he said.

“The nutrient-to-calorie ratio, however, represents the balance of building materials with the number of construction workers. If you have all the building materials and not enough workers you have all this stuff at the construction site and it’s in the way and not much is actually getting done. This interferes with proper growth. By contrast, if you have more workers [calories] than you have building materials, the workers don’t have enough to do and start causing problems; they sit around and whistle at all the pretty girls that walk by. This is not very efficient for construction. You need a balance, like having enough nails and boards and not being short on one or the other, or the right amount of workers for the amount of materials, to get things built. You want the right amount of energy, compared to the other nutrients, so you get good growth.

“There were some studies looking at yearlings fed a balanced commercial concentrate and hay, versus just oats and hay. At the end of the study, all the horses weighed the same, but the horses fed the commercial concentrate that was balanced for all nutrients were taller and leaner. The horses fed the oats and hay, taking in a similar amount of calories, were fatter and shorter. They all weighed the same but it was a different type of growth,” he said.

“We could do a comparison with young children, and the importance of having the correct amount of calories related to amount of nutrients. If you feed them meals that are fairly well balanced in nutrients but then let them drink soda pop all day, it skews the balance. If a growing child is drinking five or six cans of pop per day in addition to the regular meals, the result is usually a child carrying extra fat. That child might not be as good an athlete as the child on a more balanced diet,” Nielsen said.

Visual appraisal won’t always tell you if you are feeding a young horse correctly.

“Breeders might see a young horse at body condition five and think that’s great and that the horse is consuming the correct amount of calories. You might be providing the right amount of calories but you don’t know about the other nutrients. You may not be optimizing the growth of skeleton and muscle,” Nielson said.

People often look at the concentrates and grain, and know what’s in that, but they don’t have any idea what’s in the hay the horse is consuming.

Pasture is a great source of proper nutrition, and if young horses are out on pasture they are also running around and getting exercise— which is also crucial for proper skeletal development.

“One of the worse things you can do for a young, growing horse is keep it in a stall without adequate exercise. There has been a lot of research that shows it doesn’t matter what you feed them, if you are not allowing them to run around and be a horse, you are not stimulating the skeleton enough to become strong,” he explains.

Young horses need to be able to run and play.

“Exercise stimulates the skeleton, but the trick is how to determine what nutrients the growing young horse is getting from the pasture. You can analyze forage in the pasture, but three days later it will be different. It is constantly growing, constantly changing, even during the course of a day, from morning until night.” The sunshine, temperature changes, etc. all affect growth rate, which affects nutrient levels of the plant.

“You need to know whether the feed you are providing is fairly well-balanced. If you provide raw grain [like straight oats] with the hay or pasture, this usually skews things with inverted calcium/phosphorus ratios. Even the protein level of oats is not the greatest for a growing young horse and it’s a relatively low-quality protein in terms of amino-acid blends. By contrast, if you feed a commercial concentrate, it has been properly balanced for the important nutrients,” he explains.

Nielsen encourages breeders to analyze what they are feeding, particularly any grain mix, and the hay. A large thoroughbred farm, buying hay in bulk, usually has the hay analyzed, to know what the nutrient levels are so they can balance it properly with the rest of the diet such as concentrates or supplements.

Providing a balanced commercial concentrate is usually wise. Typically it will provide some of the micronutrients that might be lacking in the hay. Feeding young horses is tricky. “If you are trying to optimize growth with limitless access to feed, you might be getting good rate of gain—which is desirable—but unless you have things balanced appropriately you might not be getting proper structural growth to

go with it,” Nielsen says.

Mother Nature can be quite forgiving. “Some deficiencies can end up permanently stunting a horse, yet even if diets are not perfect, young horses can still often reach their destined mature size—just not as quickly. In some instances, body structure may not be as strong as it would have been if diets had been better formulated. The big problem comes when trying to grow yearlings to exhibit their best potential early on so they will sell well or be ready to begin training early,” he says.

“We often want to blame nutrition when things go wrong, but there are other factors involved, including genetics. The intricacies of interaction between genetics and nutrition can be difficult to determine. There are certain bloodlines that are very forgiving; you won’t have a problem with growth regardless of what you feed. There are also horses that are programmed for fast growth and if you don’t have the nutrients balanced correctly you will have a wreck on your hands,” Nielsen said.

If you are not getting the right nutrients in, you can’t expect a good outcome, especially with the growing horse.

“It’s like building a wall. If you don’t have mortar, the bricks won’t hold together,” he says. n

Veterinarians recommend following vaccination guidelines provided by the AAEP. These can be found on their website and are a good place to start when developing a vaccination schedule for foals, weanlings and yearlings. The best protection begins with vaccinating the broodmare at strategic times during pregnancy (for antibodies in her colostrum), and then vaccinating the foal at certain ages to build his own immunity.

Dr. Caitlin Rothacker, who did an internship at New Bolton Center and is now a member of the team at Grand Prix Equine (the largest privately-owned equine practice within Connecticut and Westchester county, N.Y.), says that if the foal is from a mare that was well vaccinated there is one set of guidelines, but if the foal is from a mare with a spotty vaccination history or had a bumpy start in life without enough colostrum, there is another set of guidelines.

Foals from well vaccinated mares should receive tetanus, EEE, WEE, and West Nile in a three-dose series, starting at four to six months. The maternal antibodies from colostrum should protect the foal during its first four to six months of life, so we vaccinate these foals during the transitional time when that protection is starting to wane.

“In the southern U.S. where vector season is longer, we recommend starting these vaccinations earlier, since foals will be at risk sooner from mosquito-borne diseases. You can start at 3 months of age in this situation,” she says.

“Rabies is a two-dose series, and we start at six months, to not have maternal antibody interference. If the dam was unvaccinated for rabies, we can begin the series at three to four months. With an unvaccinated mare, foals should also be started on their other core vaccines earlier. You can start tetanus at one to four months. The EEE, WEE, and West Nile can start at three to four months.”

A few years back there was controversy over when to give foals their first influenza vaccinations.

“We usually don’t start before six months of age, and recommend use of inactivated vaccine,” Rothacker said.

The modified live virus vaccine, via the nostril, is usually given later, in the six to eight-month range. Again, the risk of contracting the disease must be considered when making these decisions.

Dr. Julie Wilson (Turner Wilson Equine Consulting) emphasizes the fact that standard recommendations sometimes should be modified, based on risk.

“These are just guidelines, and each farm should work with their veterinarian to fine-tune a vaccination program/schedule. Until we have a way to predict when we can successfully vaccinate each individual foal [since passive immunity from maternal antibodies, which interfere with vaccination success, will wane at different times, in different foals], in some situations where there is overwhelming risk, you may need to start vaccinating earlier than recommended,” she says.

“This is definitely the case with foals in Florida, with EEE [Eastern Equine Encephalomyelitis] being such a high risk during mosquito season. We’ve seen young foals from properly vaccinated mares still get the disease. During that vulnerable period before six months, it’s better for Florida horse owners to go ahead and start vaccinating foals at two to three months rather than waiting until four to six months,” Wilson said.

“In Florida, I would start vaccinating foals for EEE at two months of age, knowing that it may not be effective yet. In this instance I would rather over-vaccinate for that disease [because it has a 90% mortality rate] than wait until six months of age to vaccinate and run the risk of losing a foal,” she says.

Thus it may be wise to delay weaning foals until they have had two doses of vaccine. For most vaccines, a third dose a month later is recommended. n