Which of the following methods is considered least invasive for animal identification?

Microchipping is regarded as the least invasive method for animal identification because it involves the insertion of a small chip, typically about the size of a grain of rice, under the skin of the animal. This procedure is quick and can be performed with minimal discomfort, often without the need for anesthesia.

The microchip contains a unique identification number that can be scanned using a special reader, allowing for easy retrieval of the animal's information without causing ongoing physical alteration or distress.

In contrast, ear notching involves removing a small piece of tissue from an animal's ear, which can cause pain and long-term changes to the animal. Tattooing requires the application of ink into the skin, which while less painful than some methods, still involves puncturing the skin and may lead to infection or irritation. Branding, which involves applying a heated instrument or liquid to mark the skin, is markedly more painful and can result in severe scarring and potential long-lasting harm.

Given these considerations regarding invasiveness, microchipping stands out as the most humane option for identifying animals.