Assessment of tetanus revaccination regimens in horses not vaccinated in the previous year.

A two-dose revaccination against tetanus is recommended for horses over 2 years old in Japan with no history of vaccination in the previous year. Here, the need for two-dose revaccination was evaluated in terms of antibody titers for each vaccine type, namely monovalent or multivalent. There was no difference in antibody titers between one- and two-dose regimens for up to 1 year, except at 8 weeks with the multivalent vaccine, and all horses had sufficient antibody titers for 1 year of tetanus prophylaxis. These results suggest that one-dose revaccination, regardless of the vaccine type, is as effective as two-dose in preventing tetanus for at least 1 year in horses not vaccinated in the previous year.

Anesthetic management with sevoflurane combined with alfaxalone-medetomidine constant rate infusion in a Thoroughbred racehorse undergoing a long-time orthopedic surgery.

A three-year old Thoroughbred racehorse was anesthetized with sevoflurane and oxygen inhalation anesthesia combined with constant rate infusion (CRI) of alfaxalone-medetomidine for internal fixation of a third metacarpal bone fracture. After premedication with intravenous (IV) injections of medetomidine (6.0 µg/kg IV), butorphanol (25 µg/kg IV), and midazolam (20 µg/kg IV), anesthesia was induced with 5% guaifenesin (500 ml/head IV) followed immediately by alfaxalone (1.0 mg/kg IV). Anesthesia was maintained with sevoflurane and CRIs of alfaxalone (1.0 mg/kg/hr) and medetomidine (3.0 µg/kg/hr). The total surgical time was 180 min, and the total inhalation anesthesia time was 230 min. The average end-tidal sevoflurane concentration during surgery was 1.8%. The mean arterial blood pressure was maintained above 70 mmHg throughout anesthesia, and the recovery time was 65 min. In conclusion, this anesthetic technique may be clinically applicable for Thoroughbred racehorses undergoing a long-time orthopedic surgery.

Effects of intravenous fentanyl administration on end-tidal sevoflurane concentrations in thoroughbred racehorses undergoing orthopedic surgery.

To evaluate the effects of IV fentanyl administration on the end-tidal sevoflurane concentration (ET(SEVO)) in thoroughbred racehorses, the ET(SEVO) required for internal fixation of longitudinal fractures was compared between horses anesthetized with sevoflurane-fentanyl (Group SF; n=9) and those anesthetized with sevoflurane alone (Group S; n=9). The loading dose of fentanyl (5.0 µg/kg) was administered over 15 min followed by a maintenance dose of fentanyl (0.1 µg/kg/min) throughout the operation in Group SF. The mean ET(SEVO) during the operation in Group SF (2.6 ± 0.2%) was significantly lower than in Group S (3.0 ± 0.3%). The plasma fentanyl concentrations (6.12 ± 0.88 to 7.78 ± 1.12 ng/ml) in 7 out of 9 horses in Group SF were stable and did not change significantly throughout the operation. The mean dobutamine infusion rate required for maintaining a mean arterial blood pressure between 60 and 80 mmHg during the operation in Group SF (0.56 ± 0.30 µg/kg/min) was significantly lower than in Group S (0.90 ± 0.16 µg/kg/min). The qualities of the recoveries were clinically acceptable, and serious complications were not observed in either group. In conclusion, continuous IV fentanyl administration reduced the sevoflurane requirement by 13% in thoroughbred racehorses undergoing orthopedic surgery; however, fentanyl was considered to be less effective in horses compared with other species.

Histopathological characteristics of an ossifying fibroma formed in the maxilla of a racehorse.

A 1-year-old male thoroughbred racehorse experienced swelling of the left upper lip. The swelling was attributable to enlargement around the incisive bone of the interdental space posterior to the third incisor in the left maxilla. Even after two operations to reduce the bulk of the mass, it continued to increase in size. Dyspnea caused by stenosis of the nasal cavity forced us to perform euthanasia, and a pathological examination was conducted. Macroscopic examination of a section of the mass revealed the formation of multiple areas of solid fibrous tissue, and trabeculae within the incisive bone which had displaced the cortical bone. On histology, the mass was composed of trabecular bone-like structures due to the proliferation and aggregation of fibroblasts. Therefore, we diagnosed it as an ossifying fibroma. Equine ossifying fibroma is characterized by development in the mandible, but was formed in the maxilla in this case. Equine ossifying fibroma has not been reported previously in Japan. This is the first case of equine ossifying fibroma identified in Japan.