The equine gastrointestinal system is extensive, with the small intestines measuring 70 feet in length alone. Because the small intestines are coiled throughout the abdomen, diagnosing a specific lesion in the small intestines is extremely challenging for equine veterinarians.
"Ultrasounding the small intestine is helpful when evaluating horses for chronic colic, weight loss, and protein-losing disorders," advised Tracy E. Norman, VMD, Dipl. ACVIM from the Department of Large Animal Clinical Sciences at Texas A&M University, who presented at the 2010 American Association of Equine Practitoners Convention, held Dec. 4-8 in Baltimore, Md.
Norman and colleagues hypothesized that nasogastric administration of water mixed with mineral oil (administered through a stomach tube) could separate the loops of small intestine and reduce gas in the small intestines. They also thought that fasting the horse could increase the value of an ultrasound examination.
Norman et al. assessed the use of ultrasonograpy in 10 horses which were eating their normal ration, fasted for 24 hours, or fasted and administered an oil/water mixture that acted as a contrast agent.
Key findings were:
- Fasting significantly improved the quality of the images obtained via transabdominal ultrasound (i.e., across the body wall); and
- Administration of the contrast agent did not significantly improve the quality of the images.
Norman noted, "Fasting appears to be a valuable technique to aid in the diagnosis of conditions that cause thickening of the intestinal wall, such as inflammatory bowel diseases, tumors of the small intestine, or enlargement of the muscular layer of the intestinal wall."
Most vets looking at horses in emergency situations don't have the option of fasting the horses; however, when the small intestine is full of fluid because it is blocked or not moving for some reason (e.g. enteritis, the inflammation of the intestinal tract), the loops of intestine are much easier to see than in a normal, fed horse, indicating a potential problem.