Effect of timing of subcutaneous meloxicam administration on indicators of pain after knife castration of weaned calves

The newly revised Canadian Codes of Practice for the management of beef cattle requires that as of 2018, calves older than 6 mo of age be castrated using pain control. Castration is a husbandry procedure commonly done without pain control, and there is a lack of agreement on an effective pain mitigation strategy specific to castration. The aim of this study was to identify the optimal time of administration of meloxicam prior to castration. Thirty-four Angus and Angus crossbred bull calves (282 +/- 28.0 kg BW) were randomly assigned to 1 of 3 treatments receiving a single s.c. injection of meloxicam (0.5 mg/kg BW): 6 h (6H; n = 11), 3 h (3H; n = 12), or immediately (0H; n = 11) before knife castration. Measurements included visual analog scale (VAS), head movement (HM), accelerometer movement (AM) and strain gauge exertion force (EF) on the squeeze chute, stride length (SL), lying and standing behavior, salivary cortisol (SC), haptoglobin, serum amyloid A (SAA), substance P (SP), and scrotal temperature (ST). Samples were collected on d -7, -5, -2, -1, and immediately before castration (T0) and 30, 60, 120, and 240 min and 1, 2, 5, 7, 14, 21, and 28 d after castration, except for VAS, AM, EF, and HM, which were obtained at the time of castration. A time x treatment effect (P = 0.01) was observed for SP, where 0H had lower concentrations than 3H and 6H calves 1 d after castration, whereas 3H calves tended to have greater levels than 6H calves 5 d after castration. Mean ST was greater (P < 0.01) in 6H calves compared to 0H and 3H calves 120 min after castration, whereas 6H and 3H calves had greater ST compared to 0H calves 240 min after castration. On d 1 after castration, 6H calves had greater ST than 0H and 3H calves, whereas 0H calves had greater ST compared to 3H and 6H calves on d 28 after castration. The SL tended (P = 0.09) to be shorter in 3H and 6H calves than 0H calves 30, 60, 120, and 240 min after castration. Number of peaks from the AM between 2 and 3 SD above or below the mean were greater (P = 0.03) in 3H and 6H calves than in 0H calves. No treatment differences (P > 0.10) were observed for the number of peaks and area for AM and EF, VAS, HM, SC, or haptoglobin. On the basis of these results, the optimal time to administer s.c. meloxicam in 7- to 8-mo-old knife-castrated calves is immediately before castration (0H), as evidenced by fewer indicators of pain and inflammation compared to 3H and 6H calves.