The differences between drugs
Pain is sometimes classified as immediate (fast) pain, and chronic (slow) pain. During painful animal husbandry procedures, there may be immediate pain associated with the procedure, as well as slower long-term pain associated with any injury and healing.
Local anaesthetics vs Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
In general, local anaesthetics deal with immediate pain, making the animal more comfortable while the procedure occurs and shortly after. Generally, local anaesthetics are immediate and short-acting, lasting for less than one hour. They provide a high degree of analgesia (pain relief) during that period, but no pain relief once they wear off. NumOcaine uses a short-term local anaesthetic (lignocaine), so will only provide any level of analgesia for less than one hour. Tri-Solfen contains two local anaesthetics, lignocaine and bupivacaine (a longer acting local anaesthetic), as well as adrenaline, and appears to provide longer analgesia (up to 24 hours has been reported) when applied to a wound, particularly in terms of reducing wound pain.
NSAIDs reduce inflammation, pain and fever. They stop the transmission of pain signals by blocking the synthesis of prostaglandins. They have been used in people (e.g. Nurofen, Voltaren) and in cattle (e.g. flunixin injections) for years, but have only recently been registered in sheep (Metacam, Buccalgesic). NSAIDs take 15–30 minutes to take effect, and generally provide pain relief for at least nine hours, but often longer. For example, Colditz et al (2019) reported meloxicam’s maximal effect 6–9 hours post treatment. Small et al (2014) reported a seven-fold decrease in adverse animal behaviours seven hours after surgical castration and hot iron tail docking with post treatment of buccal meloxicam, and only a small effect at 24 hours.
Despite being anti-inflammatory, Colditz et al (2019) reported no effect of meloxicam on inflammation and appetite in sheep, and Small et al (2014) found no improvement in movement of treated lambs or any production gain.
Take home message
Most pain relief products help with some of the pain an animal experiences, but not all. Using a combination of products will provide greater pain relief. Local anaesthetics provide relief from immediate pain but are short-acting. NSAIDs provide a longer duration of pain relief but do not deal well with the immediate pain.