Comparison of preoperative tramadol and pethidine on postoperative pain in cats undergoing ovariohysterectomy - Evangelista, Marina C; Silva, Rodrigo A; Cardozo, Larissa B; Kahvegian, Marcia A. P; Rossetto, Thais C; Matera, Júlia Maria; Fantoni, Denise Tabacchi (BMC Veterinary Research, 2014)