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Can NSAIDs be used to reduce signs of post-operative pain in calves castrated without local anaesthesia?

Although calves under eight weeks old can legally be castrated without anaesthesia or pain relief, the use of effective analgesia would improve calf welfare during these procedures

21 July 2021, at 9:00am

Calf castration is a common management practice, and while it is accepted that castration is painful, calves under eight weeks old can legally be castrated without anaesthesia or pain relief. Calves older than this must be castrated by a veterinary surgeon with appropriate anaesthesia. Both the Farm Animal Welfare Council (FAWC) and British Veterinary Association (BVA) recommend the use of local anaesthesia and longer-acting analgesia for all castrations and recommend non-steroidal anti-inflammatory drugs (NSAIDs) to manage more chronic pain.

The use of effective analgesia would improve calf welfare, even in the absence of local anaesthesia. So, it is important that you explore the evidence behind the efficacy of NSAIDs in reducing signs of post-operative pain during castration.

The evidence

Twenty studies were critically appraised; all were controlled trials and, of these, 17 were randomised. Only NSAIDs currently licensed for use in cattle in the UK were explored – meloxicam, ketoprofen, carprofen and flunixin. Studies assessed pain response by measuring physiological parameters (eg cortisol concentrations, acute phase proteins concentrations, scrotal or rectal temperature) and behavioural parameters (eg standing, lying and stepping behaviour, and specific discrete behaviours such as tail-flicking and lesion-licking).

Assessing pain

The studies showed mixed results for the efficacy of NSAIDs alone in reducing signs of post-castration pain, although 13 out of the 20 studies showed some improvement in pain indicators following NSAID administration. Pain is inherently subjective and is therefore difficult to assess objectively. Limitations of using physiological pain indicators are that some lack specificity to pain alone. Behaviours such as lesion-licking and changes in standing and lying behaviour may be more pain-specific (Millman, 2013) than physiological markers, but are more difficult to objectively assess. While objective measurement of behavioural parameters can be obtained using devices – such as pedometers as observed in 11 of the aforementioned studies – they generally cannot collect data on discrete and more pain-specific behaviours. Due to the limitations in both physiological and behavioural pain assessment methods, it is preferable to use both together to obtain the most accurate results.

Castration method

Castration method may affect the type of pain experienced and therefore the analgesic ability of NSAIDs. Of the five studies that showed improvement in both physiological and behavioural pain indicators, three investigated surgical castration and two investigated both surgical and band castration. Of the seven studies which showed no significant improvement in pain, four only investigated band castration. Future studies could explore whether band castration is less amenable to pain relief through NSAIDs.

Timing of analgesia

Twelve studies involved NSAID administration before castration and of these, four showed reduced physiological and behavioural indicators of pain and a further four showed reduction in either physiological or behavioural indicators.

NSAID administration concurrently with castration reduced both physiological and behavioural signs in one study, and either physiological or behavioural indicators in a further three.

Post-operative NSAID administration appears to be the least effective, with only two studies reporting improvement in pain signs; however, it is important to note that these studies incorporated NSAID administration at several different time points.

Choice and dose of NSAID

Thirteen studies investigated meloxicam (of which eight reported some benefit), four investigated ketoprofen (of which one reported improvements in physiological and behavioural parameters, and one reported behavioural improvements) and three investigated flunixin (of which two reported reduced cortisol concentrations). Only one study, Paull et al. (2015), reported increased pain following NSAID administration, which is thought to be due to tissue irritation due to subcutaneous injection of flunixin into the scrotum.

A further confounding factor affecting NSAID efficacy is dose and administration. The most common dose for meloxicam was 0.5mg/kg (7 out of 13 papers investigating meloxicam), and of these five papers found some improvement in pain signs following meloxicam administration. A higher dose of 2.0mg/kg meloxicam showed no significant improvement in pain (Daniel et al., 2020); however, this study investigated band castration, which, according to the appraised evidence, was less amenable to pain relief via NSAIDs.

Conclusion

Overall, it appears that NSAID administration is likely to reduce post-castration pain by some degree, with 13 out of the 20 studies identifying improvement in pain indicators after NSAID use. The degree to which pain is reduced is variable and depends upon factors including, but not limited to, castration method, specific NSAID given, dosage, administration and calf age. Of the NSAIDs investigated, meloxicam appears to be the most effective although further research is required. Future research should further investigate the effects of NSAIDs alongside local anaesthetic administered 10 to 15 minutes prior to castration, as this appears to be the most effective way to mitigate both acute and more chronic pain associated with castration.

The full Knowledge Summary, with a full reference list, can be read in RCVS Knowledge’s open access journal Veterinary Evidence – and was the winning paper in the 2021 Veterinary Evidence Student Awards.