In fact, the bill (which, by the way, has not yet been adopted, it passed two readings out of three in the House of Lords, and has not yet been considered by the House of Commons) there is no such strange statement. It talks about the ability of animals to feel, so the bill prohibits causing them suffering.
The reason for this confusion is the English word sentient, which can be translated as either “reasonable” or “sensitive.” No wonder, in English, feeling and reason are designated by the same root words; novel by the writer of the XIX century Jane Austen, known in Russian translation as “Sense and Sensibility”, in the original is called Sense and Sensibility… The full title of the bill is “On the establishment of a committee for the protection of animal senses with functions of influencing public policy regarding the welfare of animals as sensitive creatures.”
There is nothing fundamentally new for Great Britain in this formulation: it contains in the 2007 Lisbon Treaty, which was part of the British legal system as a document of the European Union. But after the UK left the EU, it turned out that the country had no law protecting animal senses; it is this gap that the new bill must fill.