The animal's only energy source is plants. Some portion of that energy goes into producing muscle and organ tissue. Some of it is converted to heat. The rest is used for respiration, digestion, thinking, walking around, dreaming, and all the other ongoing processes of life. Animals don't undergo photosynthesis, nor do they spontaneously generate energy.
Unless there's something else you're getting at here. Energy loss and trophic levels is a pretty well-understood idea.
http://kids.britannica.com/students/assembly/view/90132
Admittedly, there is a bit more nuance to the issue; for example, a cow can produce milk and meat from grass, which, for humans, creates available nutrients where there were none before. However, we could also plant that field of grass with corn or potatoes and get many more calories for the same amount of water and sunlight.
>Please explain this in more detail.
Sure! Plants are much less nutrient dense that animals. So for them to create fake meat that's equally nutrient dense as real meat, their farms have to be adequately large. You need a ton of plants to achieve the density of meat. Animals on land however are already nutrient dense. The only physical space they need is enough room to graze.
>>and sequesters carbon/methane as a side effect
>I have not heard of a farming practice that sequesters methane released from ruminants. Can you provide more information?
Scientists and farmers in this area can do a much better job explaining it than I [1], [2], [3].
[1]: https://www.ted.com/talks/allan_savory_how_to_green_the_worl...
[2]: https://www.youtube.com/watch?v=4Z75A_JMBx4
[3]: https://vimeo.com/80518559