Not a mortal sin, but it is disgusting where these practices exist, and it's a fine show of a lack of interest in the well being of the world when people simply don't care, or point to a different issue to care more about. Catholics should be at the forefront of justice, even when it is for animals. This does not mean assigning human privileges to animals-- I believe we can eat them, as God said-- but it does mean treating them humanely, and thinking about the impact that the meat industry has on the world as well.
Creation is God's, and it is good. It is not to be treated cruelly for, even God, the master of creation, took pity on his animals in the last verse of Jonah.
Not all of us can do something about everything, nor are we called to-- but those who sweep it under the rug without a second thought, their actions are offensive to God.
(Edit: if you are particularly concerned, and you don't know if your meat is coming from a safe place [don't forget those videos are just as propaganda and misleading as anything the meat industry will tell you for their side], just stop buying meat. I eat it when it is offered to me but I've only bought meat a few times in the last year. I also raise chickens so I don't have to buy eggs, which industry is likewise horrifying. Cook vegetarian dishes for your friends and family, but never talk about it-- just if they ask)