The main difference is that cavalry fighting dismounted had their own specific way of doing so, wherein companies (later termed troops) were divided into groups of four men - the same as the four riding abreast in a normal road column - and every fourth man would act as horse-holder for the other three. That means whenever you're considering unit strengths for engagements you have to deduct one-forth of the numbers of the unit fighting dismounted from the battle line. Since cavalry like Buford's were usually armed with carbines, their effective range when firing was shorter than infantry rifles - a main reason they often gave way when fighting infantry. Since they were still a mounted force, the normal tactic - as employed by Buford - was to call up the mounts held by the fourth men from the safe distance in the rear, mount up, and withdraw to the next defensible position, and repeat. Major James Kidd commanding the Fifth Michigan Cavalry in Custer's brigade described how two of the four regiments were "saber regiments" and two were "skirmishing regiments", meaning two of the four regiments in the brigade had received more training in this tactic, while the other two were usually employed in mounted charges using sabers as the prime weapon. (Though in actuality, all the regiments were at least capable of fighting mounted or dismounted.)