The sizes and breeds of horses and ponies employed underground depended upon the kind of work that they were needed for and the circumstances in which that work had to be done. The animals ranged from Shetland at 9 hands [36 inches or 91 cms] to horses of 17 hands [68 inches or 1.73 metres]. Generally ponies were about 14 hands [56 inches or 1.42 metres]

Nearly all the ponies used were male with each colliery having its own policy regarding geldings. Many collieries had their own breeding programmes, as approximately 10,000 new ponies were required annually in the British coalfields. However, when these programmes failed to meet the required numbers, ponies were obtained from as far a field as Iceland, Scandinavia, Russia, Belgium and even the U.S.A.

Often by the time a pony reached the colliery, it would have passed through several hands in the trade. Dealers from coal mining areas ranged far a field to obtain animals to supply local pits, buying in large numbers from breeders; wild pony auctions and ‘collector-dealers’ who would assemble ponies for sale to the colliery suppliers.

By law, ponies had to be at least 4 years old when employed underground and their age, as with all horses, was assessed by their teeth.