Thiamine (B1) is a member of the water soluble group of B vitamins. Following absorption it is metabolized to its active form, TPP – thiamine pyrophosphate. TPP is an essential cofactor in multiple reactions involving energy generation from carbohydrate (glucose) and branched chain amino acids.
Specifically, TPP is involved in steps needed to get energy sources burned by aerobic metabolism. For example, TPP is required for the pivotal enzymatic reaction that sends pyruvate from glucose into aerobic metabolism instead of conversion to lactate. In fact, elevated lactate is one sign of thiamine deficiency, as is impaired muscular function.
Since the primary and preferred fuel of the brain and nervous system is glucose, thiamine also is critical to their normal functioning. Thiamine deficiency has been linked to a host of neurological conditions – confusion, weakness, gait abnormalities, impaired thinking are among the signs of severe deficiency. Thiamine status has also been linked to depression or anxiety in times of stress.
Other signs of deficiency noted specifically in horses include loss of appetite, poor growth, low heart rate, even death.
Should you supplement? How much?
Full blown, potentially life threatening, thiamine deficiency has never been reported in horses eating typical diets. The minimum requirement to sustain life has been set at 3 mg/kg of dry matter in the diet – about 30 mg/day for the average horse not in significant work. Exercising horses need about 50 mg/day. There is also evidence that growing horses have more efficient growth and weight gain when fed diets that have twice the density of thiamine as the adult minimum requirement.
These are the bare minimum requirements. Do they differ from optimal intake? The answer is most likely yes. A 2017 paper in the Israel Journal of Veterinary Medicine (Laus et al) found that horses given intravenous supplementation in the form of TPP (the active form of thiamine) produced significantly less lactate on a standardized exercise test compared to horses of identical fitness.
This is similar to findings in human athletes where oral thiamine supplementation in higher than typical recommended minimums reduces lactate, ammonia and fatigue to an even greater extent than formal endurance training. Supplementary thiamine has also been found to support performance and mood under stressful conditions.
Thiamine is virtually nontoxic, with the only noted side effect of even massive doses being nausea. Horses at maintenance or in light work may not need any supplemental thiamine. Horses in heavier work schedules and/or under stress could benefit from supplementation of between 300 and 1000 mg/day for the average size horse for maximal support of metabolism and the brain.
Eleanor Kellon, VMD