What is the Number One best excuse to explain a failure to loose weight?

A: I eat too much.

B: My friends (husband, wife or family) force me off my diet.

C: I have a very slow basal metabolism.

The best excuse is “C”. It is safest to blame basal metabolism as it leaves your will power unscathed and your friends untouched. But what exactly is Basal Metabolic Rate (BMR) and how does all this relate to horses?

Let's begin by defining Basal Metabolic Rate. BMR is the amount of energy it takes for an animal to maintain itself in a state of complete physical rest, in a comfortable environment and approximately 12 hours after eating. In other words at rest but not sleeping.

To maintain normal body functions at rest, calories are burned creating heat - heat that warms the body. The amount of heat that is given off is directly proportional to the total body surface area. For example, it takes more energy to maintain a horse than a man.

There is also a correlation between body surface area and weight. The bigger the animal, the more it weighs and the more surface area it has. This means that bigger animals need more energy to maintain their basal metabolism .

But there is another factor to the equation. Not only is body weight correlated to surface area it is also related to body type. The more compact and round the animal, the less surface area for a given weight.

To account for different body types, nutritionists have added a species specific constant to the formula used for calculating the energy required for maintenance (BMR). The constant for an animal like a pig is a smaller number than for a dairy cow because the pig has less surface area for its weight than the cow. This means that if a cow and a pig weighed the same, the cow would need more energy for maintenance than the pig.

But that's where science deserts us. We all know that within any given species there are a variety of body types. There are bull-dog quarter horse types, long and lean thoroughbred types, and everything in between.

If we rely entirely on science to calculate how to feed "the horse", we are going to run into problems - the kind of problems that were graphically pointed out to us one cold Maryland winter. That year we were wintering about thirty mares at the University of Maryland Equine Research Unit. About half of these were tall and lanky broodmares while the others were short and dumpy quarter horse types.

Before going into winter, the mares were routinely weighed in September when they were in good flesh. Despite the difference in height, all the mares were pretty close to the 1000 lb standard.

Banding the mares together, we turned them out on 150 acres of winter pasture. The cold descended from the North early and by the time winter had set in, the grass was frost bitten and covered with snow. Way too soon, it was time to start supplementing their diets with hay and grain.

For the first month or so, the mares were fed in a group feeding situation. The thoroughbred-type mares got skinnier; the quarter-type mares got fatter and rounder. In fact, the shorter rounder mares were getting too fat but we were afraid to cut back on the feed because of the poor condition of the others.

It was decided to send in a team of students to watch the group. Were the fat mares driving the skinny mares away from the food?

No. Actually, the thoroughbred-type mares were chasing off the quarter-type mares. They were eating more and gaining less (a trick many of us might wish we could apply to own nutritional program.)

So why were the thoroughbred types skinner than the quarter types? The answer again relates to BMR. There must be a basic difference in Basal Metabolic Rate between these two groups accentuated by heat loss during the cold weather.

The taller slimmer mares were losing more heat as they tried to maintain their body temperature of 101.5 degrees F. in weather that sometimes had a chill factor of -40 degrees F. This made their energy requirement for maintenance, in some cases, almost double that of the shorter rounder models.

Even though it took more facilities, time and labor, our solution to the problem was to divide the herd. This situation also allowed for further testing of management techniques which might help improve the situation for all these horses subjected to such a severe environment.

One strategy that was especially effective was to feed coarse or slightly over mature hay to the mares during extremely cold weather. Since it takes more energy to digest this type of hay, it was hoped that more heat would be generated and the horses would be warmer. This seemed to work particularly well in the taller, lanky herd of mares so we decided to run a little feeding trial.

The thoroughbreds-type mares were divided into two groups: one getting 20 lbs of grain and 10 lbs of regular hay; the other group received 10 lbs of grain and 20 lbs of coarse hay. The ration of the first group contained roughly 12,000 more calories than the diet of the second. Still, in spite of this difference, the group consuming the coarse hay appeared to have less stress from the cold weather than the group eating the higher energy diet.

This concept of body surface area to body weight is also evident in the spring when horses start to loose their winter coats. Those animals that are bigger and heavier tend to shed that winter fur much sooner than the lighter, more angular individuals.

Try this experiment yourself: Next spring compare yearlings to in-foal broodmares to see which one sheds hair earlier and which one tends to keep that winter coat in order to prevent heat loss from the body surface. The answer will tell you a lot about which one of your horses needs the most feed during the colder winter months.

Here is the basic formula to calculate BMR. BMR = Y(Body Weight in kilograms).75)where Y is the body type constant for the species.

For the horse this value (Y) is 155.

Therefore the BMR for any given horse is 155 (Weightkg).75

For our average 1000 pound horse this calculates out to 155 (454).75 or 15,252 calories.

In practical terms, this means that it takes 15,252 calories to keep the average mature horse alive but doing nothing. Nothing at all but breathing. That's roughly 12 ¾ lbs of oats a day.