Horsefaq.org
A Handbook for Horse Owners
(2) A horse's colour should be good of its kind. 'Washy' colours are bad; the term denotes the faded or washed-out appearance of some coats. When the colour gets light towards the extremities it is called 'mealy'. The hairs of a well-coloured horse are dark at the points and extremities. The saying 'a good horse is never a bad colour' has much truth in it.
A horse means a stallion. A gelding is a castrated horse. A colt is usually an unbroken horse up to 3 years. A filly is usually an unbroken mare up to 3 years. A foal is a horse of either sex under 1 year. The word 'filly foal', or 'colt foal' can be used if necessary. A rig is an imperfectly castrated horse.
In purchasing a horse the age is naturally an important consideration and should be understood thoroughly. An 'aged' horse is one over 7 years. The reason for this term is that, up to 7, the age can be accurately determined by the length of and markings on the teeth. But as the horse grows older the exact year of birth becomes less certain, and unless one knows from other sources exactly what the real age is, it is safer to call him 'aged'. The age of a horse is reckoned from the 1st January, no matter when it may have been foaled. So that a horse foaled in May becomes a yearling on the 1st January following, although in reality it is then only seven months old. Hence the value, for racing purposes, of early foaling.
The age is determined by the front teeth, in the following way:
Foals, like children, have baby teeth, which are easily detected; they are small and white. But care should be taken not to mistake a two-year-old for a six-year-old mouth, as frequently happens. Looked at from the side a horse's teeth should meet evenly, touching each other almost vertically. But as age increases ie tendency is for teeth to protrude so that they meet it a slant. Horses have a 'tush', mares have none.
At 21 years the central front teeth appear. At 3 years the central front teeth are in full use. At 3 years the side front teeth are cut. At 4 years the side front teeth are in full use. At 4 years the corner teeth are cut. At 5 years the corner teeth are in use, but not fully. The rule is simple: There are six front teeth, and At 3 years old a horse has full use of the two centre ones. At 4 years old a horse has full use of the four centre ones. (Between 4 and 5 a horse or gelding cuts his tush, which is a sharp isolated tooth on each side of the final teeth.) At 5 years old a horse has nearly full use of the six teeth. At 6 years old all six teeth are in full use. At 10 years appears Galvqyne's Mark, a depression on the outer side of the corner upper front tooth; at 15 it reaches halfway; after 20 it begins to disappear, and at 30 it has gone. This is useful when making a rough guess at the age of an old horse; it is not infallible.
Notes: (1) A horse up to 1st July is called his age 'off' and after that date he is 'rising' the next year's age. (2) On the ends of the teeth, the biting surface, are to be seen black marks. These are most prominent at 6, and often disappear altogether at about 10. (3) At 7 there is a distinct notch on the upper corner tooth, where it overlaps the under one. This is sometimes removed by 'copers' and should be looked for.