Is sentience only a nonessential component of animal welfare?

According to Broom (2014), animal welfare is a concept that can be applied to all animals, including single-celled organisms that are obviously not sentient. Such a stance makes it difficult to draw a connection between welfare and sentience, and that is the book’s downfall. Some excellent points are made about sentience and there are very good discussions on animal welfare. However, unless sentience is considered the essential component of welfare, any attempt to link the two phenomena will be unsuccessful — and that, indeed, is the case with this book