Obesity associated laminitis is studied by MARE Center PhD candidate
Submitted by: Donna McDonald
Phone: 540-687-3521 ext 22
Email Address: dmcdo05(at)vt.edu
Date Added: 7/1/2008
Obesity associated laminitis is studied by MARE Center Ph.D. candidate
By: Donna McDonald
Middleburg, Va., July 1, 2008 – Laminitis has major economic and welfare implications for the equine industry, as according to a survey conducted by the USDA, apart from colic, laminitis was the most common cause for a horse or pony to be presented for veterinary treatment. Additionally, laminitis associated with consumption of “lush” pasture accounted for an estimated 54 percent of laminitis cases for which the initial cause was identifiable.
Increasing evidence indicates a link between this pasture-associated form of laminitis and the metabolic abnormalities that occur with obesity. Just as in humans, obesity seems to be a growing problem in horses. A recent study performed by the Virginia-Maryland Regional College of Veterinary Medicine Equine Field Service practice indicated that the prevalence of overweight or obesity may be as high as 50 percent in horses in southwestern Virginia.
Equine scientists at Virginia Tech have been investigating the relationship of obesity and laminitis. As part of the research program, graduate students have the opportunity to participate in research while working toward their master’s degree or Ph.D..
Becky Carter graduated from the University of Delaware in 2003 with a bachelor’s of science degree in biochemistry. Like most undergraduates, Carter was undecided as to what career path she wished to pursue. Being an avid horse enthusiast since the age of eight, the possibility of combining her interest in science with her interest in horses was a motivating factor for continuing her education with graduate studies.
Via the Internet, Carter found Virginia Tech’s Animal and Poultry Sciences department which is part of the College of Agriculture and Life Sciences. Through APSC she discovered the department offered studies focusing on equine nutrition. Coupling her interest in the health and well-being of the horse, with her excellent academic scores, Carter applied for and was granted a John Lee Pratt Fellowship to pursue her masters degree in equine nutrition through Virginia Tech.
Thus began Carter’s journey in equine nutrition. “Before I began my masters I came up to the MARE Center and spent a couple of weeks working and helping other graduate students. I did this to help get acclimated to the farm and the types of research taking place here before I started at the Blacksburg campus”, stated Carter. Having liked what she saw happening at the MARE Center with equine research, and after finishing her course work at the Blacksburg campus, Carter returned to the center along with her husband, John in the summer of 2004.
At the MARE Center, while collaborating with her research group, Carter began delving into thyroid studies in the horse. She measured thyroid hormones in ponies with a predisposition for laminitis. “Laminitis is a disease in the hoof that can be very painful, debilitating and in severe cases can lead to euthanization”. Carter stated, “These hormones were lower in predisposed ponies; however not out of normal ranges. I found that having low thyroid hormone concentrations was not a risk factor for developing laminitis on spring pasture during the few months after the hormones were measured”. It was concluded that hypothyroidism was not causing the laminitis in ponies that Carter was observing. Carter and her colleagues at the MARE Center believe that there are metabolic causes for the disease. For the past several years, under the guidance of Drs. David Kronfeld and Ray Geor, researchers at the MARE Center have been looking at how nutrients in the pasture grasses interact with the ponies’ metabolism to cause pasture-associated laminitis. “We look at insulin resistance which is a type of cell malfunction in the horse that prevents blood sugar from being taken up into the cell,” said Carter. “In the spring time of the year, when pasture sugar content is the highest, laminitis is most prevalent, presumably because ponies with insulin resistance are not able to properly metabolize the sugar from the pasture”. To ascertain that the sugar content in the pasture grasses was high enough to be considered a risk factor for laminitis, samples of the pasture were taken and to a commercial lab for analysis.
Having completed her master’s degree in 2005 under the direction of the late Dr. David Kronfeld, Carter continued to live at the MARE Center while working on her PhD. Under the direction of Dr. Ray Geor, Carter began investigating the role of obesity in changing metabolism and risk for laminitis. “I looked at different levels of obesity in horses, especially a “cresty neck”, which proved to be an increased laminitis risk”, Carter said. Carter then hypothesized that obesity causes insulin resistance through increased inflammation in the fat tissue. To prove this, Carter completed a weight gain study in which horses were taken from a moderate to an obese body condition by increasing feed intake.
Having made a connection between insulin resistance and obesity in horses, which are risk factors for laminitis in horses, Carter next looked at ways to reduce these factors. She believed exercise to be the answer and so she began her exercise studies on the same horses she used during her weight gain research. “I used the automatic horse exerciser (hot walker) which allowed me to preselect duration and speed while exercising the horses. I also used the treadmill which allowed me to use a higher intensity exercise method and to get the horse to a canter while using a heart rate monitor,” Carter said. During Carter’s horse exercise study, feed was not decreased from the horse’s maintenance level. Therefore, Carter saw modest decreases in body weight (4%) and didn’t see long term changes in metabolism. “By restricting dietary intake and increasing exercise we would expect to see a more positive affect on weight loss and improvements in metabolism in the horse. There is still much research to be done on the causes of laminitis and management strategies to avoid laminitis,” stated Carter.
Carter will complete her PhD in equine nutrition through Virginia Tech’s Animal and Poultry Sciences department this summer. Carter said, “My research at the MARE Center has afforded me the opportunity to pursue laminitis research in a post doctoral position at the University of Pennsylvania’s New Bolton Center located in Kennett Square, Pennsylvania.” Students, like Carter, who come to the MARE Center to study equine research become part of our lives here at the center. While we will greatly miss her, we understand the value of her research as it continues to better the lives of horses around the globe by improving the knowledge of laminitis in horses and ponies, and we wish her all the best in the future. She has created another milestone at the MARE Center by paving the way for our future graduate students.
Virginia Tech’s Middleburg Agricultural Research and Extension Center’s mission is to advance the health and well-being of the horse through graduate education for equine professionals, nutritional and pasture management research, and community educational programs. Located in Middleburg, Va., the center is one of 13 Agricultural Research and Extension Centers located across the state that help serve the commonwealth's agricultural needs.
For more information Donna McDonald, dmcdo05@vt.edu or 540-687-3521 ext. 22. Visit our website at http://arecs.vaes.vt.edu/middleburg
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