Horse vitamin supplements is a big industry because every concerned horse owner wants to feed them Horse Vitamin supplements.
It can be an older horse who becomes rigid or has trouble sustaining weight or it can be a performance horse who is under stress because of a tight schedule as there's a supplement available in the market for every problem. You can search online if you want to know about equine supplies.
But the question arises why a horse needs to take an equine vitamin?
From nature basically, the horse gets all the nutrients from herbs, grass etc. Natural choice means that sometimes horses find trouble living on the available cellulose so their reproduction becomes slow which results in the slow, stiff, hard and rigid body.
Once humans trained the horse they started breeding for specific qualities other than stinginess; things like size, speed, jumping ability, and pulling power.
If any animal tended toward slimness, then proper feed in the form of concentrates like grains must be given.
We know that this horse is lacking something but if a horse is fat even on the small diet then he must be lacking some underlying deficiency. Similarly, a horse in good flesh may have a dry coat which tans or changes color, easily in the summer.
It may have weak hooves, prone to splitting and breaking. The mane and tail may be small and ragged-looking, with split ends.
Depending on which supplement is missing, he suffers from problems like lethargy etc.