The local l anaesthetic In Numnuts is a powerful fast-acting drug that blocks transmission of pain signals by nerves. The local anaesthetic is injected directly where the ring is applied to the tail and scrotum. The pain of ring castration and ring tail docking commences at these sites. LA is the ideal class of drug for reducing acute pain. The marking ring disrupts blood flow to the tail and testicles. Pain develops around 2 – 5 minutes later from loss of oxygen supply, and the acute pain associated with the procedure lasts 60-90 minutes. LA reduces the conduction of pain by nerves for a similar time frame. Local anaesthetics are therefore an excellent choice for reducing the acute pain when lambs are marked with a rubber ring.
In contrast NSAIDs have a slower onset than local anaesthetics. They act by a different pathway to reduce production of chemicals (prostaglandins) that provoke tissue inflammation and pain. NSAIDs are a good choice for reducing dull and chronic pain, once the immediate and most intense phases of pain have passed.