Giving thanks implies that the animal voluntarily sacrificed his or her life so that humans might eat – and nothing could be further from the truth.
Non-human animals value their lives in much the same way that humans do, shown by the way they display fear and attempt to escape from situations where they’re under threat. It’s highly unlikely that an animal would choose to be killed for any reason never mind to provide pleasure for another species.
In any case they are not given the choice – they are farmed, slaughtered and eaten whether they like it or not. Given that, it seems quite inappropriate to say ‘thank you’ to an animal for something that was forced upon them and they most likely would not have wanted to happen.
The only way to truly respect animals is to consider their point of view and accept that they would not want to be exploited and used for your benefit – and when there are so many delicious plant-based foods available, showing them this consideration isn’t difficult to do.