> Meat production is using some parts of this energy (e.g. transportation of feedstock + food).

Everything is using energy.

Transportation is not included in the 45% (check the link in my previous comment). And AFAIK we also need to transport vegetables, using machines for agriculture, etc.

> Vegetarianism (or better veganism) sounds like the best thing to start with.

Objectively, chicken and pork have much lower emissions than beef.

Also, removing beef consumption would increase consumption of other foods so the emissions reduction wouldn't be as drastic.