Eat them, and then don't grow more.

Way more humane to let them live in squalor until the day some 14 year old slave labourer cuts their throats amiright?

(Assuming you're asking with best intent)

I'm suggesting we stop breeding "livestock" (sentient animals) into existence for a life of torture to then be killed and eaten by humans.

80% of agricultural land is used for animal agriculture. Rewilding most of that land, making some of it habitable, and the remaining converted to plant agriculture would be a far more eco-friendly solution.

What I think you're getting at with

If we stop caring for the cows, they'll die.

(paraphrased)

Which I agree is unethical; however, real world solutions don't happen immediately like that. A slow movement builds, and as demand for meat, dairy, eggs, etc. reduces, the supply will reduce over time until only a small portion of farmed animals remain. They should be cared for in a similar way that elephants on Sanctuaries or rescues are cared for.