9 C.F.R. § 352.19
Notwithstanding part 309 of this subchapter, an official establishment that wishes to slaughter horses can apply for voluntary ante-mortem inspection according to § 352.3 . Such establishments shall pay the applicable base time, overtime, and holiday rates for ante-mortem inspection in accordance with § 352.5 . Such ante-mortem inspection shall be made in pens on the premises of the establishment at which the horses are offered for slaughter in accordance with § 309.1(b) , and such establishments also shall comply with all applicable provisions of §§ 352.8 and 352.9 . If the establishment complies with all these requirements for ante-mortem inspection, FSIS will conduct ante-mortem inspection at that establishment in accordance with § 352.10 , and all other provisions in part 309 of this subchapter that pertain to horses will apply. FSIS may deny or withdraw ante-mortem inspection services at official establishments that slaughter horses for any applicable reason under § 352.6 . Official marks and devices to identify inspected and passed horse carcasses and parts of carcasses, or horse meat food products shall be those in § 312.3 of this subchapter.
9 C.F.R. §352.19