Anatomy and morphology
For better and realistic proportions, always refer to real photos of horses in the breed you want to create. This drawings are small tips on the place you can check when you find propotions strange on a model. You can create your own references for special breeds you like !
The horse body is contained in a propotional square (3 heads high and wide).
Remember that the ribcage may be different depending on the breed and the weight of the horse.
The foal height up to one month after birth is around 60 to 70% of the mother height (on withers)
The leg length represents ⅔ of his body height such as an adult.
While the foal is higher than long, the pony has shorter legs and is longer than high.
Notice the differences with a horse are the neck and back (shorter) and the legs (depends on the breed).