B Vitamins are produced in horses hindgut. However, when horses are on a high carbohydrate and/or low fibre diet, or stressed by – travel – performance pressure – change of environment – or by illness, b vitamin production can be impaired. Research has shown that B Vitamins, particularly Thiamine, can be insufficiently made in the gut and therefore lower in supply and so many horses may need supplementation, especially if access to good pasture is not available.
Signs of low Thiamine can be distracted, spooky behaviour, edgy and difficult manner. Often this type of behaviour is attributed to low magnesium levels, even though a natural diet with a small feed usually provides sufficient magnesium. Many feeds and additives contain Organic or chelated Magnesium, which is not water soluble, and so it can be overdosed to a toxic level with negative effects to the horse. Magnesium oxide is water soluble but is inorganic but less popular (there is a trend for organic), and so safer for the horse.