How much does an animal in the slaughterhouse typically eat before he is slaughtered?

I'm getting pretty tired of my omni friends accusing me of being "greedy" or "wasteful" when I eat a lot of food, considering that their diets have a lot of meat, which, every time they eat it, is the equivalent of eating ALL of the food that that animal ate his entire life in ONE MEAL. It would be impossible for me to waste as much as they do as a vegan. My question is, what is the average amount of food that an animal in the slaughterhouse typically eats before he is slaughtered? I want an exact statistic to shut them up the next time they accuse me of eating too much.