There is almost nowhere on Earth that you could hope to raise cattle on 0.5 acres per cow long-term.
For instance, the Texas Land Association gives guidance of 50-75 acres per cow for natural wooded pastures. If you develop a "managed pasture" (ie, you're driving tractors over it to spray fertilizer, have irrigation, etc) you could get that down to 2-6 acres per cow. Source: https://landassociation.org/how-many-cows-per-acre-in-texas-...
You got the numbers reversed, I said 40 acres with 20 cows. They have an additional 40 acres of roughage that can be opened up at times but its not managed grass. I live in an area that is very very fortunate for its weather and soil.
The beef we purchase produces 300 hamburgers from 1/4 cow not counting the steaks, ribs and roasts, from 40 acres of land shared with 20 others cows.