Magnesium, Vitamin E and Vitamin B1
Magnesium, Vitamin E and Vitamin B1 all play an important role in energy metabolism, hormonal control, sodium conduction, calcium metabolism and stress management. Deficient horses can show signs of nervousness, muscle weakness, poor tolerance to work and it can also predispose ‘tying up’ in performance horses. Understanding the functions of magnesium, vitamin E and vitamin B1 in the equine body can help shed some light on why adequate supplementation is so important.
Horses evolved consuming large quantities of roughage, which supplied adequate amounts of magnesium daily. Nowadays, feeds are high in other nutrients, such as calcium, which can hinder the absorption of magnesium and speed the digestive transit, so there is less time for magnesium to be absorbed (Altura et al, 1996).
When a horse is exposed to stress, there is a chain reaction of flight or fight responses. The domesticated horse is subject to high level of stress and all horses react differently (Berlin et al, 2009). For some, the stress response is always partially engaged, leading to hypersensitivity. In response to stress, the body releases hormones and nerves assist in increasing heart, metabolic and breathing rates, redistribute blood flow to the muscles, increase blood pressure, blood glucose and delay the onset of fatigue (Elin, 1994). The most significant hormone in the reaction is adrenaline, and magnesium is the key to controlling this onset.
At a cellular level calcium and magnesium work hand in hand. Calcium is involved in contracting the muscle; when a muscle cell is triggered for movement by a nerve, the cell membrane opens and calcium rushes in. This increase in calcium concentration causes a reaction and in turn the muscle cell contracts. Once the contraction has occurred, magnesium in the cell helps drive out the calcium, relaxing the muscle. This occurs in every muscle cell, at a very rapid rate (Stewart, 2011). Unfortunately, when magnesium is inadequately provided in the horse’s diet or there is an overwhelming amount of calcium, this balance is disturbed and the muscle remains stimulated and does not completely relax.
The far-reaching systemic nature of the stress response means that magnesium supplementation can benefit and prevent many health issues.
Depending on the horses workload, the NRC (2012) recommended requirements for magnesium for horses is between 8 -15 g/BW per day.
Vitamin E is an essential vitamin that needs to be supplemented in the horses diet, as they are unable to synthesize it themselves. It is first and foremost an antioxidant that plays a role in protecting cells from free radical damage.
Free radicals have an odd number of electrons, which gives them an unstable electrical charge. In an attempt to become more stable, they ‘steal’ electrons from other molecules. This causes a new molecule to become unstable, and it may not be able to perform its normal function. Free radical formation is often referred to as oxidative stress, and a chain of oxidative destruction can damage the cell and sometimes cause cell death (McBride et al, 1999). As exercise increases the, the number of free radicals increases. Free radical formation is a natural consequence of the body utilizing fat and carbohydrate stores for energy.
Antioxidants in the body control free radical damage as they bind to the free radicals inhibiting their ability to ‘steal’ electrons. To avoid damage to muscle cells during exercise, adequate levels of antioxidants must be available to counteract all the extra free radicals. As the horse’s workload increases, the requirement for Vitamin E supplementation increases (White et al, 2001). Signs of oxidative stress in working horses include muscle soreness and slower than normal recovery from intense exercise.
The NRC (2012) recommends horses be supplied with 50 IU/kg DM or approximately 1 IU/kg BW per day.
Vitamin B1, also known as Thiamine is a water-soluble vitamin. This means it is not stored in the body and needs to be replenished daily. Thiamine plays a vital role in carbohydrate metabolism, converting carbohydrates to energy and nerve transmission, development of the myelin sheath that surrounds the nerve to enable efficient transmission of signals (Irvine et al, 2011).
Hard working horses, or those on high grain, low forage diets may have reduced availability of thiamine in the hindgut due to stress or hindgut acidosis. The NRC (2012) requirement for thiamine daily is 5 mg/kg DM for horses in work and 3 mg/kg DM for all others.
Altura, B.M., Altura, B,T. 1996. Role of magnesium in patho-physiological processes and the clinical utility of magnesium ion selective electrodes. J Clin Lab Invs.56, 53-67.
Berlin, D., Aroch, I. 2009. Concentrations of ionized and total magnesium and calcium in healthy horses. Effects of age, pregnancy, lactation, pH and sample type. Vet J. 181. 305-311.
Elin, R.J. 1994. Magnesium: the fifth but forgotten electrolyte. J Clin Pat. 102, 612-622
Irvine C. H. and Prentice N.G. (2011) The effect of large doses of thiamine on the horse. NZ Vet J, 10, 86-88
McBride, J.M and Kraemer, W.J. (1999) Free radicals, exercise and antioxidants. J Str Cond Res. 13, 175-183.
Stewart, A.J., 2011. Magnesium disorders in horses. Vet Clin North Am Equine Pract. 27, 149-163.
White, A., Estrada, M., Walker, K., Wisnia, P., Filgueira, G., Valdes, F., Araneda, O., Behn, C. and Marinez, R. (2001) Role of exercise and asorbate on plasma antioxidant capacity in Thoroughbred racehorses. Com Biochem Physiol. 128, 99-104.