The effect of timing of oral meloxicam administration on physiological responses in calves after dehorning with local anesthesia

Abstract

Dehorning is a painful husbandry procedure that is commonly performed in dairy calves. Parenteral meloxicam combined with local anesthesia mitigates the physiological and behavioral effects of dehorning in calves. The purpose of this study was to determine the influence of timing of oral meloxicam administration on physiological responses in calves after dehorning. Thirty Holstein bull calves 8- 10 weeks of age (28-70 kg) were randomly assigned to one of three treatment groups: placebo-treated control group (CONT) (n=10), calves receiving meloxicam administered orally (1 mg/kg) in powdered milk replacer 12 h prior to cautery dehorning (MEL-PRE) (n=10) and calves receiving meloxicam administered as an oral bolus (1 mg/kg) at the time of dehorning (MEL-POST) (n=10). Following cautery dehorning, blood samples were collected to measure cortisol, substance P (SP), haptoglobin, ex-vivo prostaglandin E2 (PgE2) production after lipopolysaccharide stimulation and meloxicam concentrations. Maximum ocular temperature (MOT) and mechanical nociceptive threshold (MNT) was also assessed. Data were analyzed using non-compartmental pharmacokinetic analysis and repeated measures ANOVA models. Mean peak meloxicam concentrations were 3.61 ± 0 .21 μg/mL and 3.27 ± 0.14 μg/mL with average elimination half-lives of 38.62 ± 5.87 h and 35.81 ± 6.26 h in the MEL-PRE and MEL-POST groups respectively. Serum cortisol concentrations were lower in meloxicam-treated calves compared with control calves at 4 h post-dehorning (P=0.0004). SP concentrations were significantly higher in control calves compared with meloxicam-treated calves at 120 h after dehorning (P=0.038). PgE2 concentrations were lower in meloxicam-treated calves compared with control calves (P=0.001). MNT was higher in control calves at 1 h after dehorning (P=0.02) but meloxicam-treated calves tended to have a higher MNT at 6 h after dehorning (P=0.07). There was no effect of timing of meloxicam administration on plasma cortisol concentrations (P= 0.69), SP concentrations (P=0.86), haptoglobin concentrations (P=0.86), MOT (P=0.90), or MNT (P=0.99). However, PgE2 concentrations in MEL-PRE calves were similar to CONT calves after 12h post-dehorning, while MEL-POST calves had lower PgE2 concentrations for 3 d post dehorning. These findings suggest that meloxicam reduced cortisol, SP and PgE2 after dehorning but only PgE2 production was significantly affected by the timing of meloxicam administration.