Larger animals like buffalo and cows tend to have more fat on them compared to smaller animals like deer, making them better sources of fat for human consumption.

“intriguingly you know the larger the animal the more the fat so if you're eating a deer that you hunted there's not gonna be any fat on that your ancestors would not have had enough fat on that to live but if you're eating a buffalo or a cow there's a decent amount of fat on a buffalo or a cow for a human to live on”