A new method of administering local anesthesia for calf disbudding: Findings from a comparative on-farm study in New Zealand.

Anesthesia of the horn bud for calf disbudding commonly is attained by injection of local anesthetic over branches of the cornual nerve, with anesthesia achieved in 3 to 20 min. With experienced and trained staff, this method is effective in 88 to 100% of calves. Variability in response and time of onset can compromise calf welfare if calves are disbudded before anesthesia is attained. Proposed legislative reliance on effective local anesthetic as the minimal method of pain relief for calves at disbudding means that administration of local anesthetic must achieve a repeatable level and rapid onset of analgesia. We describe an alternative method of local anesthesia administration that uses local site infiltration of anesthetic over the horn bud. However, this method has not yet been scientifically validated. This study assessed differences between disbudding using the cornual nerve block and disbudding with local anesthesia administered by local site infiltration. Efficacy of local anesthesia was assessed at 30-s intervals after administration by absence of reaction to 3 consecutive needle pricks over the horn buds. Behavior indicating pain was assessed during disbudding and scored from 0 to 3. Calf behavior was also recorded for 3 h after disbudding. Accelerometer data loggers were fitted to each calf for 24 h before and after disbudding to assess lying and standing times. Median time to cutaneous desensitization for local infiltration was 60 s compared with 225 s for cornual nerve block, and the variance in time to desensitization was less with local infiltration. Calves disbudded under cornual block had a larger behavioral response (indicated by a graded aversive body reaction) than calves disbudded under local infiltration. A multivariable model predicted that the mean body reaction score would be 0.6 for calves disbudded under local infiltration and 1.2 for calves disbudded under cornual block. There was no difference in any behaviors between the treatment groups in the 3 h after disbudding. Method of analgesia had no effect on lying time over the 24 h after disbudding. In this study, local infiltration was at least as effective in providing analgesia for disbudding as the cornual nerve block. Our results suggest that a more consistent, effective level of analgesia during disbudding was achieved using local infiltration and that there was no difference in postoperative expressions of pain.

Effects of local anesthetic and a nonsteroidal antiinflammatory drug on pain responses of dairy calves to hot-iron dehorning.

This study examined the effects of a nonsteroidal antiinflammatory agent (NSAID) on physiological responses of calves immediately after hot-iron dehorning (DH) and during the time that local anesthetic (LA) wears off (2 to 3 h) after this procedure. Forty-six calves (33 +/- 0.3 d of age) were randomly assigned to 6 treatments: hot-iron DH versus sham DH with either no pain mitigation, LA alone, or LA with NSAID (i.v. Meloxicam). Eye temperature (measured using infrared thermography) was recorded every 5 min for 3 h after treatments. Heart rate (HR) and heart rate variability (HRV) were recorded continuously; for analysis of HRV, short segments of 512 interbeat intervals were examined. After DH without LA or NSAID, HR increased by 35 +/- 3.0 beats/min in the first 5 min and remained elevated above baseline for 3 h. The HRV around the time of DH did not differ between treatments; however, the root mean square of successive differences decreased from 68 to 41 +/- 12.6 ms immediately following DH without pain relief, suggesting a decrease in vagal tone at this time. Between 2 and 3 h following DH with LA, there was a decrease in eye temperature (-0.6 +/- 0.1 degrees C), an increase in HR (8 +/- 3.0 beats per min) and changes in HRV. Changes in HRV at this time included a decreased high-frequency power and an increase in the low-frequency power and low-frequency/high-frequency ratio, indicating a change in sympatho-vagal balance. The changes in eye temperature, HR, and HRV between 2 and 3 h following DH with LA indicated the onset of pain coinciding with the time that the LA effects wear off. In addition, this study demonstrated that the combination of LA and NSAID mitigated the onset of pain responses when the LA wanes.

Eye temperature and heart rate variability of calves disbudded with or without local anaesthetic.

The possibility that pain can be detected from changes in eye temperature and heart rate variability (HRV) during disbudding was examined in thirty calves, randomly assigned to four treatments: 1) sham handling (control), 2) local anaesthetic (LA, cornual nerve injection) and sham disbudded, 3) sham LA and disbudded, 4) LA and disbudded. During a 40 min sampling period, maximum eye temperature, behavior and HRV parameters were recorded continuously. One week later, twelve disbudded calves were injected with adrenocorticotrophic hormone (ACTH) or saline and maximum eye temperature was recorded. There was a rapid drop in eye temperature during the 5 min following disbudding without LA (P<0.05). Eye temperature then increased and was higher than baseline over the remaining sampling period following both disbudding procedures (P<0.001), a response which could not be explained by increased physical activity LA increased eye temperature prior to disbudding (P<0.001). Heart rate increased (P<0.001) during the 5 min following disbudding with and without LA, however, LF/HF ratio only increased during this time (P<0.01) following disbudding without LA. Eye temperature did not change following ACTH, suggesting that hypothalamus-pituitary-adrenal axis (HPA) activity is not responsible for the changes in eye temperature following disbudding. The increase in LF/HF ratio following disbudding without LA suggests an acute sympathetic response to pain, which could be responsible for the drop in eye temperature via vasoconstriction. HRV and eye temperature together may be a useful non-invasive and more immediate index of pain than HPA activity alone.