EFFECTIVENESS OF TOLAZOLINE IN REVERSING XYLAZINE-INCREASED SEDATION IN CALVES

Objective-To test effectiveness of IV administration of tolazoline hyd rochloride in reversing xylazine hydrochloride-induced sedation in cal ves. Design-Prospective study. Animals-12 female and 12 male Friesian- cross calves from 5 to 7 months old. Procedure-Calves were assigned to 1 of 4 treatment groups. Calves were given xylazine (0.3 mg/kg [0.14 mg/lb] of body weight, IM). Twenty minutes later, calves were treated with saline (0.9% NaCl) solution (1 ml/50 kg [1 ml/110 lb], IV) or tol azoline (1, 2, or 4 mg/kg [0.45, 0.9, or 1.8 mg/lb], IV). Behavioral a nd physiologic measurements included elapsed time from xylazine admini stration to recumbency, arousal and standing times after reversal drug administration, heart rate, and respiratory rate. Results-Mean (+/- S D) recumbency time for all calves was 5.4 +/- 1.8 minutes. Compared wi th administration of saline solution, all 3 doses of tolazoline signif icantly decreased arousal and standing times. Mean arousal time for ca lves receiving saline solution was 27.8 +/- 11.5 minutes. Administrati on of tolazoline at 1, 2, and 4 mg/kg resulted in mean arousal times o f 4.7 +/- 3.8, 0.9 +/- 0.5, and 0.7 +/- 0.3 minutes, respectively. Mea n standing time for calves receiving saline solution was 38.8 +/- 2.8 minutes. Administration of tolazoline at 1, 2, and 4 mg/kg resulted in mean standing times of 14.0 +/- 11.0, 3.0 +/- 1.2, and 2.4 +/- 1.1 mi nutes, respectively. Clinical Implications-For routine use, tolazoline doses of 1 to 2 mg/kg should suffice. In cattle, IV administration of tolazoline reverses pharmacologic effects of xylazine, thereby hasten ing recovery from xylazine-induced sedation.