Metabolism of a human as an example of a large mammal
Because so many humans are interested in their weight and thus their diets, there is abundant free information on the web about the caloric requirements of humans and the caloric content of foods. The following information was obtained from the web in just a minute or so.

I have calculated the beef required to feed a human to an age if 20 years, assuming constant consumption. Of course babies doesn't eat as much, which would decrease the amount. However, the numbers from the web assume only moderate physical activity, and most animals have to work hard for a living. Humans today live to a much older age, but animals in the "wild" live just past their age of effective breeding or age when they are eaten; thus the 20 year life time I have used here. In any case these numbers are only intended as an approximation: the conversion effeciency is about 2 percent.

 life time (days) 7,300 cal per day (160 lb man) 2,300 cal needed per life time 16,800,000 cal per kg of beef 3,600 kg beef eaten per life time 4,700 kg beef eaten per kg man 65 per cent effeciency (man/beef) 1.5
However, in "Natural History of Marine Animals, 2ed", on pg 13 MacGinitie and MacGinitie suggest an effeciency of 10 percent for layers of a food chain. Let's split the difference here, and pick 5 percent as an approximate value (after all it's just an educated guess).