With the advent of ivermectin-based dewormers in the late seventies, horse owners could control the large strongyle. Migration of this extremely destructive strongyle's larvae up the mesenteric arteries and the ensuing damage was largely responsible for limiting the horse's life to around the 20-year mark. This limit on a horse's life meant we rarely had to deal with geriatric diseases of horses. Since the use of this dewormer, the incidence of life-threatening infarction of the blood supply to the bowel has steadily declined. Horses can now be expected to live well into their 30s or beyond, depending on many factors, including the level of health care. However, with the increase in older horses we are seeing more problems that result in weight loss despite continuing a good diet.
This article discusses diagnosis of common problems that cause weight loss and lists some of the most common problems, lists treatment options, and provides links to articles with detailed information.
Many geriatric patients can be safely fed a maintenance ration designed for all horses without modification. In cases where the horse has loss of body condition and no other existing disease, the horse should be fed a very palatable, easily masticated, easily digested, dust-free diet that has a higher protein content (12-16%), maintenance levels of calcium (1%), and slightly elevated P content (0.4 - 0.65%), maintaining a Ca:P ratio of close to 1.5:1.
Older horses may be more sensitive to cold and adverse conditions. Be sure the horse always has shelter to get out of the wind and rain when cold. They may also not compete as aggressively for food, so they should be fed separately from their pasture mates. Older horses may not adapt as rapidly to change, particularly when moved into a new situation. Changes should be made slowly the horse carefully monitored for successfully coping with the new situation.
As horses age, attention should be placed on maintenance of body condition, in the 4-5-6 range (1-10 scale). Whenever presented with an older horse in poor condition, a complete physical examination, a thorough oral exam, and fecal test should be performed. The most common problems encountered in the aging horse with unexplained weight loss are:
If any systemic problems, particularly depression and/or weight loss, are identified on the physical, blood should be collected for laboratory tests. These should include:
When laboratory results between a healthy group of geriatric (20 yrs of age) horses and young horses (5 yrs of age) is compared the only differences were an elevated median corpuscular volume (MCV) and decreased plasma ascorbic acid concentrations. This decrease in plasma ascorbic acid concentration may be associated with the increase incidence of Cushinoid Disease in geriatric horses and has been the basis of the recommendation of vitamin C supplementation in older horses.
From the history, the physical exam, and laboratory tests the following problems may be identified:
Inadequate or Inappropriate Feed:
Dental Disease
An annual, or in some cases a biannual, oral
examination should be performed on all geriatric horses. Older horses may be
afflicted with a variety of forms of dental disease. Just as other parts of the
body wear out, so do the teeth. Long incisors, loose cheek teeth, broken,
missing, misshaped, sharp points, and/or malaligned teeth are common findings on
oral examination in older horses. When possible, dental corrections should be
made, but care is taken to avoid over-correction.
With severe dental disease, the ability to masticate hay and grains is impaired even with good dental care. Besides switching from sweet feeds to extruded concentrates, changing from hay to grass cubes free choice and alfalfa cubes at 0.5% bwt will help the horse ingest forage. If there still is a problem the cubes can be soaked. In the most severe cases soaked pelleted forage may be required. Soaked beet pulp is another choice for horses with poor teeth but does require some manipulation of the diet to balance the calcium and make up for missing nutrients
Pituitary Dysfunction and Cushinoid Disease
Common symptoms are unexplained weight loss,
long hair coat and/or slow shedding of the winter coat, excessive drinking and
urination, and chronic founder. Pergolide 0.003 to 0.005 mg/lb orally daily.
This is more effective than cyproheptadine, but more expensive. Geriatric horses
with Cushinoid Disease may have a reduced insulin response or glucose
intolerance. Many of these animals may be found to have hyperglycemia and
altered mineral (particularly phosphorus) balance. In cases of high blood
glucose sweet feeds (3% molasses) should be avoided. Vegetable oil can be added
to the diet for energy.
Chronic Kidney
Disease
Chronic disease of the kidneys may result in
failure of their ability to remove toxins from the blood. Though depression,
weight loss, and increase drinking and urination (PU/PD) can be expected, other
more common diseases, like Cushinoid Disease, also result in these symptoms. The
diagnosis is generally made on the results of the laboratory work demonstrating
elevated BUN and Creatinine. In cases of geriatric horses with renal disease,
beet pulp, legume hay, should be avoided. Grass hay with a protein content of
8-10% should be fed. Vegetable oils (1-2 cups/d) can be fed if the animal is a
low body condition score. Supplemented B-vitamins and Brewers yeast may be
beneficial. Ralston reported a higher incidence of renal calculi in aged mares
and geldings fed alfalfa hay.
Choke
Older horses may have reduced esophageal
functions and salivary production. As choke appears more common in aged horses
who do not salivate or chew well, pelleted feeds may need to be avoided, unless
presoaked in water.
Recurrent Colic
Older horses have a higher incidence of colic. A
University of Auburn study reported that of 104 referral colic cases in horses
above 17 yr old, grazing difficulties, lipomas, and dental disease were the
major predisposing causes. Cohen suggested that some of the factors predisposing
to colic were being stalled 50% of the time, recent (2 wk) changes in housing,
and being fed water from a bucket. Access to a pond, access to pasture, or
feeding extruded feeds, all decrease the incidence of colic.
Other
Considerations
A chronic founder which may also be associated
with Cushinoid Disease is a common problem in older horses and particularly
ponies. Foot care should be meticulous to prevent further painful episodes and
abscesses. A starch intake should be curtailed and a fiber intake increased. If
Cushinoid Disease is possible, pergolide therapy should be instituted.
Chronic pain from arthritis will result in a decreased food intake. The careful use of nonsteroidal anti-inflammatory drugs, intra-articular injections, and oral PSAG and other chondroitin sulfates may improve the overall quality of life and feed intake.
Geriatrics should be provided shelter but allowed free access to pasture. If they are fed with younger, more aggressive horses, they should be fed separately. On the other hand having a companion may make him more comfortable.
In the case of chronic liver (hepatic) disease, both high fat and high-protein diets should be avoided. Modify diet to a lower protein--perhaps 10% of high quality protein. Soybean meal would be an example.
Chronic infection in horses displays as, recurring abscesses, skin lesions, or possibly recurrent respiratory, including sinus infections, disease. Cushinoid disease a common cause of decreased immune function and should be treated with pergolide, if immune problems are evident. Vitamin C 10 gm twice daily and Brewer's Yeast 2 to 4 oz. daily may be of some benefit.
More and more it is becoming obvious that immune function is an important component of parasite resistance, even in horses that are dewormed regularly. Older horses, and particularly those with Cushinoid disease, may require more frequent deworming with increased dosages. However care must be taken deworming debilitated or heavily parasitized horses as they may be more sensitive to the effects of dewormers. Use of daily strongid pellets is a good option for those who are having problems,
No matter what the cause of weight loss it represents that too few calories are being consumed for the current conditions. It is imperative that any problems, particularly dental disease and Cushinoid Disease, be addressed to help resolve the problem but weight loss always indicates the need to review the quality and balance of the diet and after correcting imbalances, increase the caloric intake of the horse.