Which of the following is an example of refinement per the three Rs of Russell and Burch?

Refinement in the context of the three Rs (Replacement, Reduction, Refinement) refers to strategies that improve animal welfare and minimize pain and distress in research. The option citing the use of a new blood collection technique that causes less pain and distress actively enhances the living conditions of the animals involved by ensuring that their experiences are less invasive and traumatic. This aligns perfectly with the principle of refinement, which aims to improve the methods of animal research to reduce suffering.

In contrast, the other options do not fit the criteria for refinement. Choosing a less intelligent animal does not inherently improve the welfare of the animals used; it simply shifts which animals are used without addressing their treatment or experience. Reducing the number of animals used relates to the principle of reduction, focusing on minimizing the number of subjects in research rather than improving their conditions. Lastly, using only non-endangered species pertains to ethical considerations in conservation and species protection rather than directly improving the welfare of animals within a research setting. Thus, option A is the clear example of refinement.