Ahimsa is a Sanskrit word meaning "non-injury" or "harmlessness". As one of the yogic niyamas or prohibitions, it specifically denotes harmlessness to other sentient beings in thought and deed.
It seems evident to me, both from personal experience and from reading the research of others, that sentience is not a quality limited to human beings alone. My cats are thinking, feeling creatures; so are the cows, pigs, chickens, and sheep that the farming industry treats as machines and economic units. Furthermore, the provenance of the natural processes that they go through in living out their lives naturally belong to them, and not to me; I would not drink the milk of a human mother, because that milk is intended for her baby. So it is with a cow and her calf, or a goat and her kid, or a sheep and her lamb. I have no revulsion at the idea of eating the unfertilized eggs of chickens, but the idea of keeping a chicken for the purpose of having an egg machine repels me, and I refuse to support it.
The practice of biology and medicine is also affected by extending sentience beyond humans. It renders medical testing on animals absolutely unconscionable. Acknowledging sentience in other species does not prohibit testing using computerized simulations, or tissue cultures, or human beings who are capable of consenting because they understand the risks. Acknowledging sentience makes the mass killing of fish, turtles, frogs, rats, pigs, cats, and others for the purpose of dissection into mass murder, but does not prohibit the sourcing of animal cadavers from those that have died naturally.
None of this means that animals are above humans, or equal to humans. No one species is equal to another, since they all serve different purposes in their environments. An animal does not hold property rights the same way that a human does, but in our incredible talent for abstraction, we can assign an animal a right to a habitat that is diverse in the resources with which it evolved. We can also extend definitions of consent and custody to our fellow beings, inasmuch as it is reasonable to do so.
I am convinced that all humans have in them the capacity to understand sentience the way that I do. I am also convinced that many humans deny this capacity with great energy, because they fear the loss of those things to which they are accustomed to having as a result of the exploitation of other sentient beings. I understand that fear, having lived with it for the first 21 years of my life, and recognize that I am unusual in having renounced it. I do not expect others to change their behavior based on what I do or say, as nice as it would be if they did. This does not mean that I am silent, nor does it mean that I never become angry or impassioned when I see injustice being done. I am harmless, but I am not voiceless or toothless.