Hot, dry Tucson, Ariz., doesn't conjure up images of equine nutrition research, but leading animal scientists convened there May 31-June 4 to present their latest findings on a variety of equine science topics. The following article highlights the equine nutrition portion of the 2005 Equine Science Society Symposium.
"Not all fat is created equal," said Kelly Spearman, MS, graduate student in the Department of Animal Science at the University of Florida. "Some fatty acids might be more beneficial that others." Spearman set out to find the best fat supplement to supply essential fatty acids (omega-6 and omega-3) to lactating mares.
"The practice of providing supplemental fat to the equine diet has become increasingly popular in the horse industry," explained Spearman. "In addition to increasing the energy density of the ration, fat supplementation has been shown to have various positive effects on exercise metabolism and other physiological parameters."
With regard to lactating mares, fatty acids are thought to play an important role in foal development. "Because essential fatty acids have the potential to influence inflammation and immune function, supplying these fatty acids in greater amounts or specific proportions in the milk may be of benefit to the nursing foal," Spearman noted.
Thirty-four lactating Quarter Horse and Thoroughbred mares were used to study the differences between corn oil and mixed oil (corn oil and linseed oil) added to their diets. Spearman allowed the mares free-choice access to hay while they were being fed the oil supplement.
Spearman found that the foals suckling mares fed the mixed oil had greater concentrations of fatty acids in their blood plasma than foals from the mares that were only getting corn oil, and suggested this might benefit the foal in terms of immunology.
Feeding for Bone Density
Bone density is a major factor to a young horse in training. Youngsters with greater bone mass are less likely to suffer catastrophic and potentially career-ending bone-related injuries. While the goal of many feed regimens for young horses in training is to increase bone density, it has been thought that diets high in protein could actually decrease bone density via a negative calcium balance. Research now might be pointing the finger elsewhere.
Holly Spooner, a graduate student in the Department of Animal Science at Texas A&M University, said a negative calcium balance could create acidosis (high blood pH), which might affect bone cells and prevent their repair and formation. High protein intake has specifically been associated with hypercalciuria (the excretion of abnormally high concentrations of calcium in the urine) and reduced bone density.
However, a feeding trial using high levels of protein did not show a decrease in bone density. Utilizing 10-month-old horses, Spooner fed them a ration of concentrates and Coastal Bermuda hay. The control group was fed 14.5% crude protein; the test group was fed 19.75% crude protein. Spooner noted that during the 128-day study, all horses grew normally and there were no significant differences observed due to diet.
"Analyses of serum failed to indicate any negative effects of the high protein diet, as serum calcium, serum phosphorus, and blood pH all remained within normal limits," said Spooner. While an increase in protein in the diet caused calcium absorption to be somewhat lower (although urinary calcium loss was not different), she concluded that in contrast to other studies, bone density was not affected by excess dietary protein.
"It appears then that in this study, excess dietary protein did not cause metabolic acidosis, and while calcium absorption was reduced in horses consuming excess dietary protein, there was no effect on resulting calcium balance on bone density," concluded Spooner.
Antibiotic resistance is a major concern in the livestock industry. "The main concern is that antibiotics used to treat specific human pathogens are also used to treat livestock," said Lance Baker, MS, PhD, associate professor of animal science at West Texas A&M University. It is speculated that if pathogens become resistant, not only will livestock suffer, but humans might also be affected because common pathogens will no longer respond to antibiotic treatment. The risk of pathogen resistance has been sufficiently influential to cause regulatory officials in the European Union to ban particular antimicrobials and antibiotics.
"In order to maintain efficient production in commercial agriculture, alternative treatments need to be developed and tested," said Baker. "One non-pharmaceutical alternative to antibiotics is the use of mannan oligosaccharide (MOS)."
MOS is a naturally occurring antimicrobial that lives in the cell wall of yeast. When MOS enters the body through digestion, it serves as an attachment site for Gram-negative bacteria, thereby preventing the bacteria from hooking up with regular body cells and causing disease.
Previous studies on pregnant mares fed MOS showed that their foals' levels of IgM (immunoglobulin-M, or the antibodies mares pass to foals via colostrum) were higher than non-supplemented foals. It was suggested from that study that the MOS supplementation might have caused the mares to secrete additional antibodies in the colostrum, and that the foals receiving these antibodies were better able to cope with microbial challenges to the digestive system.
While the results of this study in mature horses showed that there was no significant effect on white blood cells after feeding MOS, there was an increase in mean eosinophils (white blood cells active in allergic diseases, parasitic infections, and other disorders) and packed cell volume (the percentage of red blood cells circulating in the blood stream), said Baker. These could be used to help ward off disease. He noted that further research might be warranted to determine the effects of various amounts of MOS supplemented, as feeding a different amount of the supplement might create a different result.
Horse Feed Glycemic Index
Glycemic indexes are available for many human foods and rank food according to how it affects blood glucose levels, said Anne Rodiek, MS, PhD, professor of animal science at California State University in Fresno. Foods with a high glycemic index quickly release glucose in the blood when digested. Low glycemic index foods break down slowly, releasing glucose gradually into the bloodstream.
Ranking equine feed by glycemic index might help feed companies develop rations for horses that have special needs and require diets with a lower amount of starch, such as horses with Cushing's disease, laminitis, or those that are obese.
Rodiek measured the blood glucose responses when broodmares in good weight were fed 10 different feeds: Steam-rolled barley, steam-rolled corn, oats, commercial sweet feed (steam-rolled corn, oats, barley, and molasses), jockey oats (also referred to as heavy oats), flaked rice bran, alfalfa, loose beet pulp, loose soy hulls, and flaked wheat bran.
"The highest blood glucose response came from sweet feed," said Rodiek. Oats and corn had the next-highest blood glucose responses, respectively, followed by jockey oats, barley, wheat bran, beet pulp, alfalfa, rice bran, and soy hulls.
Rodiek grouped the feeds into high, medium, and low glycemic index groups, which is similar to how human foods are categorized. Sweet feed, oats, and corn were placed in the high category; jockey oats, barley, and wheat bran were in the medium category; and beet pulp, alfalfa, rice bran, and soy hulls were in the low category.
It was noted that with the exception of alfalfa, the feeds with a low glycemic index all took the longest time for a horse to consume.
Insulin Sensitivity is Predetermined--Sort of
Repeated exposure to high-glycemic feeds can have detrimental effects, began Tania Cubitt, a graduate student in the department of animal/poultry science at Virginia Polytechnic Institute and State University.
"Fetal development is dependent on the intrauterine environment. Whatever the dam is eating affects the fetus," stated Cubitt. The fetal horse lives off the constant placental supply of glucose during its growth and development stages. However, when the foal is born, he only gets an intermittent supply of glucose from feed, whether it is milk or forage. This radical change in diet over a relatively short period of time has an effect on insulin sensitivity and can affect growth rate, metabolic efficiency, and susceptibility to certain diseases (namely metabolic disorders).
Previous studies in obese geldings fed meals high in starch and sugar found those horses to be insulin-resistant and more prone to metabolic disorders.
Studying two crops of Thoroughbred foals (40 foals total) kept on mixed grass/ legume pasture, Cubitt found that plasma glucose concentration and plasma insulin concentration both declined as the foals aged, thus resulting in an increase in insulin sensitivity. "This increase (in insulin sensitivity) was especially evident from about 40 to 210 days of age," said Cubitt.
"The present results in foals confirm an adverse effect of chronic adaptation to repeated high-glycemic meals that has been observed previously in weanlings and mature Thoroughbreds," said Cubitt.
To keep insulin resistance from occurring later in life in these Thoroughbreds, Cubitt suggested feeding pasture alone or pasture supplemented with a feed rich in fiber and fat during growth and when they reach maturity.
NRC Equine Project Update
The revision of the 1989 National Research Council (NRC) Nutrient Requirements of Horses is underway, and it is to be released to the public in early 2006. The project objective is to prepare a report that will evaluate scientific literature on the nutrient requirements and management techniques for horses and ponies in all stages of life.
Laurie M. Lawrence, MS, PhD, professor in the Department of Animal Science at the University of Kentucky and chair of the project, described the revisement process.
"The NRC 6th revised edition was initiated in fall 2003," said Lawrence. The committee appointment occurred in February 2004, the initial committee meeting was in March 2004, and committee conference calls and public information meetings have been ongoing since then, she said.
Sponsors for the revised publication include Kellogg Endowment Funds, American Feed Industry Association, American Quarter Horse Association, American Paint Horse Association, Equine Science Society, and North American Equine Ranching Information Council.
Additions to the revised manual include a section on nutrient management, said Lawrence, which will have better feed composition tables, the amino acid content of common feeds, and the fatty acid composition of fat sources.
"We will be using feed composition tables already available in other NRC publications (such as swine and dairy cattle)," she said, so the information provided in the revised version will be a better average of feed composition.
A computer program will also be created that is more useful than the previous one, allows more inputs, and contains a ration analysis component, she said. A CD is also a possible addition to the revision, said Lawrence. Putting pictures in the publication is cost-prohibitive, but they can easily be included on CD.
The creation of a derivative publication(s) is also being discussed, said Lawrence, although this depends on time and money available. "This is an initiative to produce user-friendly publications that might include body condition scoring and forage identification and composition," she said.
Lawrence said the revised text will have more information on the digestion of nutrients and nutritionally related problems. Also added will be requirements for special needs horses, such as those with HYPP and COPD. Noted Lawrence, "Even though there are numerous publications on what you should feed these horses, if there is no comparative data, we won't consider it."
Lawrence also said, "It is undecided what place nutraceuticals will have in the publication." Commented a committee member from the audience, "Because of FDA regulations, there are some things we aren't going to address. If it isn't a 'nutrient,' we can't put it in."
Lawrence said the committee is looking for quality data to support nutrient requirements for horses--data that doesn't necessarily have to be peer-reviewed.
For more information on this project, see www.nationalacademies.com.
"No" for Nutraceuticals
Courtney Welch, graduate student in the department of animal science at Texas A&M University, found that mature horses fed pure glucosamine and pure chondroitin sulfate had no detectable amounts of either substance in their blood plasma. She said these findings do not support the theory that orally dosed glucosamine and chondroitin sulfate nutraceuticals are readily available to the joints through the bloodstream.
Ulcers in Lesson Horses
It is well documented that horses in competition and strenuous exercise regimens are at an increased risk for stomach ulcers, said Jennifer Nadeau, MS, PhD, assistant professor in the department of animal science at the University of Connecticut. Yet out of 80 adult horses in the school's riding program, only 11% of the horses had ulcers. She concluded that "Horses utilized in their own environment, regardless of activity level, have a lower incidence of ulcers."
Christa Iacono, graduate assistant in the Department of Animal Science at Texas A&M University, found that horses transported to slaughter over a 20-hour period do not need to be watered. Iacono found horses that were provided water had little differences in physiological terms compared to those that did not receive water.--Marcella Reca
About the Author
Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.
POLL: Horses Living With Livestock