The USDA APHIS database has published the numbers of horses inspected in 2011 by each of the recognized HIOs.
SHOW 19,696
PRIDE 16,467
KY-HIO 15,468
NWHA 13,827
FOSH 3,354
IWHA 3,003
WHOA 2,999
MFTHBA 2,838
HAWHA 2,148
WIWHA 2,122
SSHBEA 2,101
OHA No data published