'Splint' is the term used to describe a bony hard lump that can appear where the splint bone and the cannon bone touch. When they first appear, the horse is often slightly lame, this lameness can last up to 6 weeks.
These infections spread when there is direct contact between horses and they usually occur in the summer or autumn period, when it is dry and dusty, or at the end of winter.
Rain scald is a skin condition caused by Dermatophilus congolensis ; an organism that is widespread.
A healthy horse, free of worms and on a healthy diet will have a rich glossy coat, so long as it doesn't have a skin infection eg ringworm.
There are several serotypes of this bacteria that can infect a horses gut. Salmonella typhimurium appears to cause more severe symptoms than others.