Roughly 1% of the cattle produced in the US are grass fed (source below). The rest are fed in feed lots and receive primarily a diet of corn and soy. The rule o

Roughly 1% of the cattle produced in the US are grass fed (source below). The rest are fed in feed lots and receive primarily a diet of corn and soy. The rule of thumb is that for each step you go up the food chain, an order of magnitude of biomass efficiency is lost-- that is, you have to give an animal 10 calories of feed to produce 1 calorie of meat. In beef, the caloric and protein efficiency metrics are 3%, meaning that you're feeding the cow 33x as many calories and grams of protein as you're getting out of it (source below). This is incredibly inefficient and is one of many reasons that a meat-based diet is not sustainable for a growing population and particularly a growing (global) middle class. https://iopscience.iop.org/article/10.1088/1748-9326/aad401#:~:text=Currently%2C%20'grass%2Dfinished',current%20US%20supply%20%5B12%5D https://iopscience.iop.org/article/10.1088/1748-9326/aad401#.... https://iopscience.iop.org/article/10.1088/1748-9326/11/10/105002 https://iopscience.iop.org/article/10.1088/1748-9326/11/10/1...