Nutrition for Rehabilitating the Starved Horse

Dr. Carolyn Stull and her team of equine welfare experts provide new guidelines for refeeding starved horses

"Kung K'ai" (Emaciated Horse), by Yuan Dyn

It is difficult to comprehend the long-term neglect and surrounding situation that produce such a devastated, depressed creature as a starved horse. The bones are so prominent that the skeleton appears to belong to a larger horse, the head is disproportionately large compared with the body, and the tail is always low and motionless. But the low hanging head tells it all. The ears barely move to any sounds in the environment, no extra energy is spent interacting with herd mates. The eyes are dull, without expression, without expectations.

Researchers from the UC Davis Center for Equine Health conducted a survey to assess the prevalence of starved horses in California and found the results quite disturbing. Among the responders to the survey were animal control and humane society organizations in 36 counties, with an estimated equine population of 1,041,560. Of this number, 2,177 horses were found to be severely malnourished. The most common reason for these cases was owner ignorance, followed by economic hardship.

A research team comprised of Dr. Carolyn Stull (UC Davis Veterinary Medicine Extension), Dr. Anne Rodiek (California State University, Fresno), Dr. Christine Witham (private clinician), Dr. Pamela Hullinger (California Department of Food and Agriculture), and Kelly Weaver (UC Davis Veterinary Medicine Extension) has been studying the problem. Funded in part by Purina Mills, Inc., the study provides a standard body condition scoring system to assess the weight status of a horse and compares different diets for refeeding the malnourished horse. In both humans and horses, abrupt refeeding can cause dysfunction of the body's metabolic systems, which can lead to failure of the heart and lungs and ultimately to death. The goal of this research is to provide new information and guidelines for recognizing and treating malnourished horses.

This horse has a body condition score of three. The ribs can be observed easily, even with the horse's winter coat, the tail head is prominent and can be felt easily, and the hip bones are rounded and protruding. (above and below right). Note the dip in the withers in front toward the neck and behind toward the back, exhibiting little or no fat deposit around this area.

At left, the hip shows an inverted V shape with the spine at the apex, representing a lack of fat deposition

What Happens During Starvation

During the starvation process, the horse initially uses any fat and carbohydrate stores in his body to supply energy for metabolism. This is the normal process for any healthy horse: fat and carbohydrates are used for energy, exercise, brain function, circulation, etc., and are then replaced with nutrients from food. The cycle is constant and never-ending, even during sleep. In a starved animal, once this source of fat and carbohydrate is gone, energy is derived from the breakdown of protein. While protein is a component of every tissue, there are no inert stores of it in the body such as there are for fat and carbohydrates. Consequently, the starved body uses protein not only from muscles, but also from vital tissues such as the heart and even gastrointestinal tissues-tissue that is necessary for life. The starved body cannot select which tissue protein will be metabolized for energy. As time goes by, the horse's survival is in a precarious situation. When a horse loses more than 50% of its body weight, the prognosis for survival is extremely poor.

The Refeeding Problem

Refeeding starved animals, including humans, is not an easy process. In humans suffering from starvation caused by illnesses such as anorexia, cancer, or gastrointestinal obstruction, patients can develop "refeeding" syndrome when they are given concentrated calories, and this in turn can lead to heart, respiratory, and kidney failure usually 3 to 5 days after the initial meal. This same syndrome has been reported in the literature for horses. Thus, our research team wanted to develop a refeeding program for horses that would minimize these effects and enable the horse to return back to normal body weight. Our goals were to test feeds that were commonly available and used in horse rations, so the refeeding program could be implemented easily in any area of the country.

Experimental Diets for Refeeding

We selected three types of feed that were very different in nutrient composition: alfalfa hay, oat hay, and a commercially available complete feed consisting of grain, molasses, fat, and alfalfa. Alfalfa is known to be high in protein (20%) but low in carbohydrate starch (3%). Oat hay is high in fiber but low in protein (7%). The complete feed represented a feed high in carbohydrate concentration, with 19% starch. The three types of feed were given to 22 starved horses that were brought to the UC Davis research site as representative of horses rescued by equine organizations. Horses were fed one of the three diets over a 10-day rehabilitation period. The researchers focused on this time period as critical to successfully transitioning the gut from a starved state to a fed state. Even though the diets were different in composition, they were fed in amounts that were equivalent on a caloric basis, so that horses assigned the oat hay diet, for example, received the largest volume of feed, while the horses on the complete feed received the smallest amount but the same number of calories at each meal.

This horse has a body condition score of five (above). She appears very smooth, with no skeletal prominence. Her neck and withers blend smoothly into her shoulders. Ribs do not show, and the loin and hip are nicely rounded.

Right, this horse has a score of nine. Note the obvious crease from his spine sunk between fat deposits on either side.

Which Diet Worked Best?

Our results with the complete feed were very consistent with human studies conducted 20 years earlier using concentrated calories. As the horse ate the high-carbohydrate diet, insulin was released in response to the high level of starch. The job of the hormone insulin is to store the carbohydrate in cells for future energy use, but it also simultaneously draws the electrolytes phosphorous and magnesium from circulation into the cell. Since the starved horse has no stores of electrolytes, this depletion may lead to kidney, heart, and respiratory failure. These effects do not occur with the initial meal but usually several days to a week later due to the repetition of insulin release following a high-carbohydrate meal and the cumulative depletion of electrolytes. The oat hay diet was very bulky and caused diarrhea in several horses. Several essential nutrients such as phosphorous and magnesium were low in the oat hay compared with the other diets; thus, this diet did not support a successful rehabilitation. The alfalfa had the best results due to its high composition of quality protein, but also the major electrolytes, phosphorus and magnesium. Since alfalfa hay is very low in carbohydrate content, there were minimal effects due to insulin response.

In a subsequent feeding study, we compared an alfalfa hay diet to a diet of combination alfalfa hay and corn oil. Equine diets usually do not contain much fat, but in recent years the use of corn oil to increase the energy density of a meal has been widely used in nutrition programs for older horses and in horses undergoing intensive training programs. The two diets were fed again on an equal-calorie basis. Although the corn oil had no harmful effects, substituting calories from corn oil for alfalfa decreased the total nutrient content of phosphorous and magnesium in the diet. Thus, the response to the diet combining corn oil and alfalfa showed a decreasing blood phosphorous level over the 10-day period, which was not advantageous to the rehabilitation. Again, the alfalfa diet was the most effective at delivering the necessary nutrients in the correct amounts to the starved horse.

Our research showed that starved horses had very different responses to several diets. We found that the best approach for initial refeeding of the starved horse consists of frequent small amounts of high-quality alfalfa. This amount should be increased slowly at each meal and the number of feedings decreased gradually over 10 days. After 10 days to 2 weeks, horses can be fed as much as they will eat. The horse will show signs of increased energy after about two weeks. Ears, eyes and head movement will be the first noticeable movements. Some weight gain can be achieved in one month, but three to five months usually are needed to rehabilitate back to a normal body weight. Veterinary care and nutritional advice should be sought as complications can arise.

 

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