By Katherine K. Williamson, DVM, Manager, Veterinary Services, Land O'Lakes Purina® Feed
One of the most common manifestations of health problems in horses is poor feed consumption and horse weight loss. Trying to discover the ultimate cause for these health problems in horses can be a long and costly endeavor for horse owners, and very frustrating for veterinarians and feed dealers. The following outline covers some of the more common causes of poor feed consumption and horse weight loss. This outline is by no means all-encompassing, but it at least can offer a place to start.
Medication - Many medications, particularly nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics, can induce adverse effects on the gastrointestinal tract and other organ systems.
NSAIDs - Drugs in this category include bute (phenylbutazone), flunixin meglumine, ketoprofen, naproxen, firocoxib. These drugs are often used in combination, particularly in athletic horses, for musculoskeletal inflammation and pain.
Problems encountered when using these drugs include overdosing, chronic usage, multi-drug interactions, and hypersensitivity in certain horses (especially to bute). These drugs can produce oral, gastric, esophageal and colonic ulcers. They can also produce kidney damage and liver toxicity - all of which can manifest in poor appetite and weight loss.
Clinical signs associated with adverse effects to these drugs and that may be incorrectly attributed to feed failure include: weight loss, diarrhea, inappetance, colic, poor hair coat/hoof quality, anemia and low protein (hypoproteinemia).
Antibiotic therapy - Antibiotics are used to treat a wide range of bacterial infections. Commonly used antibiotics in adult horses include penicillin, trimethoprim/sulfa, metronidazole, ceftiofur (Naxcel, Excede), enrofloxacin (Baytril) and gentamicin.
Certain antibiotics, including trimethoprim/sulfa and penicillin, have been more commonly associated with diarrhea in horses. However, it should be noted that any antibiotic has the potential to induce an adverse effect. Diarrhea is thought to be induced by a disruption of the normal gut microflora due to the antibiotics' action on the bacterial population of the gut.
Medical Conditions - There are numerous medical conditions that can result in poor feed intake and utilization. Below are some of the more commonly seen conditions.
Oral/dental conditions - Oral ulcers, wave mouth, dental hooks and points, retained caps and missing molars can all affect chewing and grinding, which is essential to proper feed utilization in the gut. Additionally, injuries or neurological conditions can affect the lips, tongue and cheeks, making it difficult for the horse to pick up feed and chew it adequately.
Esophageal abnormalities - Tumors, ulcers, erosions, strictures (particularly those associated with prior episodes of choke) and neurological abnormalities affecting swallowing and peristalsis (passage of feed down the esophagus and into the stomach) can all affect feed consumption.
Gastric issues - Ulcers, cancer, and delayed gastric emptying can greatly affect appetite and intake amounts leading to weight loss.
Small intestinal abnormalities - These can lead to maldigestion and malabsorption of nutrients, preventing the horse from effectively utilizing what it is eating. These conditions may be inflammatory in origin or due to cancers such as lymphoma. Many of these conditions are chronic.
Colitis - This is a very broad term for inflammation of the large intestine. Colitis can be caused by many different things, and usually results in at least some degree of diarrhea and protein loss into the gut. This category can be broken down into different classes of causes:
• Infectious- Salmonella, Clostridium spp., Lawsonia, Neorickettsia risticii (Potomac Horse Fever)
• Parasitic - Strongylosis, bots, cyathostomiasis (encysted small strongyles)
• Toxic - NSAID's, antibiotics, cantharidin (blister beetle) toxicosis, arsenic poisoning
• Miscellaneous - carbohydrate overload, sand enteropathy
Colic - Horses that have undergone severe episodes of colic and/or colic surgery commonly experience restricted access to feed, inappetance (sometimes prolonged), poor gut motility, poor absorption, and fragile bowel tissues, all while faced with an increased energy demand due to the healing process. Lack of intake in the presence of increased energy demand can result in very rapid, and often profound, weight loss.
Age - Aging horses can experience many problems that can result in poor intake and weight loss, including but not limited to Cushing's syndrome (PPID), diarrhea due to poor water absorption in the large colon, dental issues such as tooth loss and wave mouth, decreased saliva production leading to difficulty swallowing and poor digestion of feed, pain associated with arthritis, chronic diseases of the kidneys and liver, and loss of nutrient absorptive capacity in the small and large intestine.
Respiratory diseases - Long-term respiratory diseases such as pleuropneumonia and recurrent airway obstruction (RAO, heaves) greatly increase a horse's calorie needs while often suppressing appetite. Additionally with RAO, dietary restrictions regarding hay and dusty grains may be necessary, and many of these horses must be kept outdoors where they may be exposed to inclement weather (further increasing caloric demand). The end result may be significant loss of body condition.
Chronic diseases - Virtually every chronic disease will result in poor feed efficiency and some loss of body condition. Specifically, melanoma, lymphoma, liver and kidney disease can affect horses of all ages, but are most prevalent in senior horses. These can lead to ill thrift and poor body condition and hair coat.
Chronic pain - The effect that pain can have on the appetite and calorie needs of horses cannot be underestimated. Laminitis, osteoarthritis/degenerative joint disease, fractures, tendon and ligament injuries or degeneration, and navicular syndrome are just a few examples of diseases that can result in sustained pain in horses and lead to dramatic weight loss.