The issue is not that the cow becomes fat, the issue is how do humans digest eating other species.

Cow’s milk is optimized for making baby cows grow into full-grown cows in two years. Humans have drunk cow’s (and goat’s) milk for ages when human milk was lacking. Obviously human babies are not baby cows, and the enzymes and bacteria are not optimized for growing baby humans. Drinking non-human milk it is no longer needed in most places in the world, but is a tradition and REALLY big business.

Human cells produce cholesterol. Cows produce cholesterol. Human bodies are not optimized for breaking down and expelling cow cholesterol. So eating a lot of beef tends (obviously everyone is different, but the causation is clear) to lead to excess cholesterol in humans, and all the health issues that come with blood ways blocked by plaque buildup.