I have posted information from the 30 Jun 76 horse returns for each company and the regimental HQ. This comes from Hammer's original edition of "Men with Custer."
These returns probably include all the horses riden by men detailed within the regiment, detailed to Terry's HQ and Column, and any horses that may have been taken aboard the "Far West" before the regiment marched from the Rosebud. They may also include any horses known to have been left at Ft Lincoln, Ft Rice, and the Yellowstone/Powder River Depot.
It wouldn't account for privately owned horses, but probably would account for 7th Cavalry horses used by officers. It would not include Quartermaster horses which might have been used by surgeons and scouts as saddle and pack horses.
Total 7th Cavalry Regiment horse returns for 30 Jun 76