Endurance.Net Ridecamp Archives

In the Eleanor Kellon article she metions that horses can get their
daily maintenance needs of chloride from 8.5 pounds of hay or 5.5 pounds
if supplemeneted with enough salt to meet their sodium needs.

Since I feed my horses between 20 and 30 pounds of hay a day (it takes
them about four days to go through about a 100+ pound bale of grass plus
the 5-8 pounds of alfalfa that he gets on top of that) I am having
trouble seeing how this would be a problem.  At endurance rides, in
addition to having a few days worth of hay in their gi tract, they will
consume more than they normally do at home.

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It has been established that the intestinal contents of a horse contain about 14 mg of chloride per kg of body weight, so a 500 kg horse will potentially have 7000 mg or 7 grams available from this "reservoir" at any particular time. The electrolytes from food or supplements do not stay in the intestinal tract for long. They are absorbed by a combination of passive diffusion - i.e. from high concentrations in the gut to lower concentrations in the extracellular fluids on the other side of the intestinal lining - and by active absorption. It takes about 4 hours after electrolytes are consumed for levels to equilibrate out. Any excess is removed by the kidneys.

 

Regardless of what the diet was in the days preride, from available information you are only starting with 7 grams of chloride available from that source at time 0 on race day (before the horse eats anything).

 

10 kg (22 pounds) of hay on the average, assuming 0.75% chloride, could provide about 112.5 grams of chloride; 15 kg (33 pounds) about 127.5 grams. Sounds like a lot, but we know absolutely nothing about the digestibility of chloride from forages, whether it simply leaches out in the small bowel and equilibrates in the first 4 hours after eating or whether it is more "time released" with fermentation in the small bowel. If we assume it's all available within 4 hours of the horse having eaten, how much is available when the horse starts the ride depends on how much he ate before starting. If we call it 4 kg, that's 30 grams of chloride for a total of 37 grams.

 

The problem comes in with sweat composition. Sweat losses for a 500 kg horse over one hour will range from 27.5 grams to a high of 110 grams with very heavy sweating. That's per hour.

 

To put it another way, it would take 8 pounds of a 0.75% chloride hay to support just 1 hour of the lowest rate of chloride loss in sweat. 0.75% chloride in a hay is actually a bit on the high side.

 

The horse can also "steal" chloride from the extracellular fluid, the fluid outside the cells and outside the blood stream. This is a limited source, however. It's really small wonder that chloride deficits severe enough to show up as hypochloremia and alkalosis begin to appear as quickly as 2 hours into a ride.

 

Eleanor

 

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Eleanor M. Kellon, V.M.D.
Equine Nutritional Solutions
58 Maple Farm Road
Ephrata, PA 17522