No, beef and lamb are the most energy consuming sources of meat. (A dairy producing cow is different.)

https://en.wikipedia.org/wiki/Feed_conversion_ratio

    For cattle, a FCR range from less than 5 to more than 20 kg feed dry matter per kg gain may be encountered.[

Whereas for chickens:

    Poultry has a feed conversion ratio of 2 to 1.

I believe you, but I'm very surprised. That has larger animals almost universally less efficient than smaller animals, which is the exact opposite of the expected efficiency due to Kleiber's law: https://en.wikipedia.org/wiki/Kleiber%27s_law

>a cat, having a mass 100 times that of a mouse, will have a metabolism roughly 32 times greater than that of a mouse.

And yet this is saying that a mice sized animal should be expected to have the same, or perhaps even better Feed conversion ratio than a cat sized animal.

Again, I believe you, but it makes no sense.

The larger livestock will usually have a much longer lifespan. It has to keep its flesh heated above ambient for that entire lifespan. If Mouse A lives 100x longer and puts on the same weight and achieves the same stature as Mouse B, it's spent ~100x as much energy getting to the same physiological place as Mouse B.

Again, that's simple mass efficiency. We can also talk about other efficiencies, like cost of feed versus cost of meat.

They are not more efficient in terms of how many acres are required to produce a given amount of calories.

Cows are slaughtered at 80 weeks while chickens are slaughtered at 6 - 8 weeks. That extra order of magnitude of basal metabolic rate is where the energy gets consumed.

Not really. There's a basic thermodynamic inefficiency as organisms get larger, and consume farther away from the energy source, in this that being the sun.

How are cattle consuming farther away from the energy source than chickens?