Keep the environment familiar. Animals seem to recover from surgery quicker when housed in familiar environments and handled by familiar persons. Maintain a stable environment. Removing excessive noises or other environmental stresses helps reduce anxiety. Accustom the animal to your laboratory procedures.
Fear can be a big component of pain perception.
One way to relieve fear and its accompanying stress is to familiarize animals with the routine procedures, such as blood sampling, so they know what to expect. Interact with the animal. Talking, stroking and petting it can reduce restlessness, rapid breathing, increased heart rates and other signs of discomfort. Use some common sense here, because this would not work for wild animals. Handle the animals appropriately.