Veterinarians ensure a healthy future

Like any neonate, a newborn foal depends on its mother's milk as its primary source of nutrition for the first few months of life. According to the National Research Council (NRC) Nutrient Requirements of Horses 2007, foals begin to suckle within one to two hours of birth.

Thoroughbred foals nurse about 10 times an hour for the first day for about 60 to 80 seconds at a time. For the first month, a Thoroughbred foal suckles about 45 minutes daily, with milk consumption at about 15 kg/day. At first, feral neonates have been noted to nurse 6 to 8 percent of the day, decreasing to about 2 percent by 8 weeks of age.1

"The timetable of foals getting up, standing and suckling is important, not just in regard to receiving colostrum and its immunoglobulin content, but also because the foals only have a little bit of liver glycogen in their system," says Mary Rose Paradis, DVM, MS, DACVIM, of Tufts University Cummings School of Veterinary Medicine. "Usually that amount starts to be used up and is gone within a couple of hours or so. So foals need to have that colostrum to help bring their blood glucose back up. The glycogen begins to fall within two hours, as does their blood glucose, which is then a trigger for them to stand and nurse to get it.

PHOTO COURTESY OF MARY ROSE PARADIS, DVM, MS, DACVIM, TUFTS UNIVERSITY CUMMINGS SCHOOL OF VETERINARY MEDICINE.

"A lot of the sick foals we see that are less than 24 hours old are very hypoglycemic because they never got that source of colostrum, and, therefore, they are depleted in blood glucose," Paradis continues. "Colostrum is important because it is different in composition than regular milk, so if foals get a colostrum feed, then they are probably good for about 15 hours or so, even if they didn't get any additional milk. The colostrum is appreciably higher in energy (also protein and vitamins A and E)—so its benefit lasts longer—and in crucial preformed antibodies needed within eight to 12 hours. The frequency of a normal foal nursing is about seven times an hour. When that occurs, obviously they have a high need for food, and at each feeding they are probably going to get about 80 ml of milk, which is almost half a liter per hour. You are then looking at a normal 50-kg foal consuming about 12 to 15 liters of milk per day."

The foal's changing GI anatomy

A newborn foal's gastrointestinal tract is quite different from that of an adult horse. In a foal's first month of life, the small intestine is the site of most growth, growing in both length and diameter, which increases the surface area of the villous surface for the digestion and absorption of the milk meals. The large colon plays a minor role. During this first part of a foal's life, the small intestine is the absorptive surface for its liquid diet.

"They really don't have enzymes to digest any of the other foods yet, so lactase is the prominent enzyme," Paradis says. "At 2 to 3 months of age, they get maltase, which helps digest some of the other things they might consume at that age, such as creep feed or small amounts of forage. At 4 months old, maltase takes over, and the lactase decreases."

Although owners want to have some food out so that the foals can recognize what hay, grain and other feedstuffs are, foals primarily learn feeding behavior from their dam, according to Paradis. At first though, they are not going to get much of any other nutrition except from milk, so it's important that they have a good source of milk.

During the second month of life, a foal begins to develop the cecum and the large colon as organs of digestion. However, nutritionally, the foal still depends on mare's milk as the primary source of nutrition. Over the next three to five months, the cecum and large intestine enlarge and begin to populate with microorganisms that assist in breaking down the structural elements of fibrous feeds.

Learned feeding behavior

With the foal and mare at pasture, foals are known to consume forage as early as day one, and by 1 week of age, they are eating solid food about 8 percent of the day. According to the NRC Nutrient Requirements of Horses 2007, by 3 weeks of age, foals spend almost 50 percent of the daylight hours eating solid feeds, pasture and creep grain.

Dams allow their foals to eat grain along with them, introducing foals to grain and other solid feeds at an early age. Foals confined with their dams will learn to eat solid food relatively soon and will begin to wean before six months, especially preferring grazing pasture vs. hay and grain.

The mare's nutrition

Is it necessary to supplement the prelactating mare so she can feed her foal with the proper concentration of nutrients within the milk, or is she able to mobilize that herself?

"If healthy, she is able to mobilize that herself," Paradis says. "But after the foal is born, there is huge demand on the mare to make milk, so if she's not getting sufficient calories, she's probably going to lose a lot of weight to her foal. You don't want to get a mare fat during pregnancy, but you also don't want her to be thin."

The average 1,100-pound mare will produce about 3 percent of her body weight in milk daily during the first months of lactation. The foal uses the energy from milk for both growth and exercise, about 175 kcal/kg/day, with an average weight gain of 2 to 4 pounds daily during the first month, almost doubling its weight within that period.

As a result, the mare needs to be on a ration to meet the NRC recommendations for energy intake and nutrient intake and ensure that her body condition score is appropriate for a healthy pregnant mare. "So you need to think about increasing her energy intake, particularly after the foal is born," says Paradis.

Transitioning to solid food

During the lactation phase, most owners will begin to give creep feed to foals to get them used to solid feed. Unless it's a food-aggressive mare, Paradis suggests letting the foal pick at whatever is presented to the mare. "If I wanted to feed the foal, per se, I would use a feed specifically for foals, or feed milk pellets, which you can mix in a sweet feed for the foal to transition to eating solid feed on its own as weaning approaches."

The foal can eat the dam's hay or eat with her at pasture. Pasture is excellent, not only for forage consumption, but also for developing motor skills as they're running around with others.

Most people wean foals between 4 to 6 months of age, and that's when the maltases in the large intestine are starting to function better. "So at that time, one might want to have a separate feeding tub for the foal," Paradis suggests.

Keeping tabs on nutrition

Monitoring the mother's bag and the foal's behavior can help you head off feeding problems early. (See the sidebar "Growing concerns"article below for additional factors to consider during foal development.) "If the foal is constantly at the mare, trying to get milk, and the udder is really flat, that probably means the mare is somewhat agalatic—she is not producing enough milk—and the foal is hungry," says Paradis. "You won't see appropriate foal weight gain in that situation. If the mare has a huge bag, one that is streaming and dripping all the time, it probably means that the foal is not nursing enough. And that is worth investigating."

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.

Reference

1. Duncan P, Harvey PH, Wells SM. 1984. On lactation and associated behavior in a natural herd of horses. Anim Behav 1984;32:255-263.

Growing concerns

Consider these additional facts about foal development, nutrition.

>Before birth, the bone begins as cartilage. During the last few months of development, three to four months before birth, the cartilage begins ossification. At birth, almost 80 percent of the bone is somewhat mineralized.

>At birth, as noted by Laurie Lawrence, PhD, professor of nutrition, University of Kentucky, a foal has 17 percent of its bone mineral content and 10 percent of its mature body weight. Thoroughbreds, similar to other horses, will reach 84 percent of their mature height and 46 percent of mature weight by six months, 94 percent of height and 65 percent of weight by one year, and almost complete their growth—reaching full height and 90 percent of mature weight—by 22 months. Unlike height and weight, bone mineralization takes more time since horses are at 68.5 percent of total bone mineral content by six months and 76 percent by one year. They don't reach maximal bone mineral content until 6 years of age.

> From birth to 1.5 years, during the period of early development, all of the foal's body systems are functioning, but the musculoskeletal system is changing markedly, as bones are elongating, putting on mass and solidifying and muscles are gaining in bulk and strength.

> Throughout the body, proper skeletal development is critical to the horse's long-term health and ability to move soundly. Without proper formation, the young foal may develop skeletal deformities and other conditions that may lead to bone and joint degradation and developmental bone disease later in life.

> As foals grow, the bones (especially the long ones) are laying down protein and minerals. The organic material of the bony tissue is a collagen matrix of highly cross-linked protein, which makes up about 80 to 90 percent of the bone mass. The remaining 10 to 15 percent of the organic material is noncollagenous proteins.

> Foal growth primarily includes proper muscle and bone growth. As a major portion of foal growth, bone turnover is a process of continual maintenance and repair and homeostasis. The cells associated with bone resorption are osteoclasts, while bone formation is the function of the osteoblasts.

> Skeletal muscle makes up about 50 percent of the body's mass. As the fetus' muscle develops during the latter stages of pregnancy, glycogen (the muscle store of energy) increases to provide the muscle with a high store of energy at the time of birth and provides energy so the foal can run within hours of parturition.

>Growth rate matters. Growing too slowly may not result in a preferable size at a particular age or may keep a horse from reaching its optimal stature. Growing too fast is a concern for creating skeletal problems that may affect a foal's eventual athletic performance and health. Do not allow a growing horse to put on excess weight or grow too quickly because it might affect skeletal fitness at a later age. Growth potential is not based solely on genetics but may be modified by other factors, including management practices (see "Risk factors for equine osteocondrosis" in the August 2012 issue).

> Once foals begin eating solid food, a typical foal grain ration contains about 1.4 mcal digestible energy per pound. A foal should probably eat about three pounds of grain per day to support the desired growth rate. Foals should have restricted, not unlimited, access to supplemental creep feed. The foal should be properly fed a specific amount, which can be adjusted as the body condition of the foal is continually monitored.

> Regardless of food intake, sufficient paddock exercise for a foal is a necessity to ensure healthy skeletal integrity.