What is the primary purpose of the "3rs" concept from russell and burch?

The 3Rs by Russell and Burch are known to be the "alternative methods" to improve the treatment of laboratory animals, at the same time to advance the quality of science that uses animals for studies.

The 3Rs are Replacement, Reduction, and Refinement.  Replacement is defined as minimizing the pain and suffering of the animals used in research. Reduction is for reducing the number of animals being used, and using healthier animals. Replacement is using alternative to animals such as tissue cultures and computer models.

The 3Rs have a wider range than merely inspiring another course of action to animal testing but goal to develop animal well-being and scientific excellence where the use of animals cannot be evaded. These 3Rs are now explicit in legislation governing animal use in many countries. It is normal to exploit the first letter of each of the three 'R' principles to avoid uncertainty and clarify mention to the 3Rs principles.