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

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 to 10 wk of age (28-70 kg), were randomly assigned to 1 of 3 treatment groups: placebo-treated control group (n=10), calves receiving meloxicam administered orally (1 mg/kg) in powdered milk replacer 12h before 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 and mechanical nociceptive threshold (MNT) were also assessed. Data were analyzed using noncompartmental pharmacokinetic analysis and repeated measures ANOVA models. Mean peak meloxicam concentrations were 3.61±0 0.21 and 3.27±0.14 μg/mL with average elimination half-lives of 38.62±5.87 and 35.81±6.26 h for MEL-PRE and MEL-POST, respectively. Serum cortisol concentrations were lower in meloxicam-treated calves compared with control calves at 4 h postdehorning. Substance P concentrations were significantly higher in control calves compared with meloxicam-treated calves at 120 h after dehorning. Prostaglandin E2 concentrations were lower in meloxicam-treated calves compared with control calves. Mechanical nociceptive threshold was higher in control calves at 1h after dehorning, but meloxicam-treated calves tended to have a higher MNT at 6h after dehorning. No effect of timing of meloxicam administration on serum cortisol concentrations, SP concentrations, haptoglobin concentrations, maximum ocular temperature, or MNT was observed. However, PgE2 concentrations in MEL-PRE calves were similar to control calves after 12h postdehorning, whereas MEL-POST calves had lower PgE2 concentrations for 3 d postdehorning. These findings support that meloxicam reduced cortisol, SP, and PgE2 after dehorning, but only PgE2 production was significantly affected by the timing of meloxicam administration.