B12 is basically never made by eukaryotes. We humans use bioreactors or traditional fermentation cats to have bacteria do the job. Ruminants like cows get B12 by fermentation in the gut. Animal with smaller guts like chicken need it in food like us, generally via fermented food. There is no significant difference in bioavailability that I know of for B12, but there’s an argument to be had that meat is more palatable than pills or weird fermented acquired-taste foods.

Iron is probably the only nutrient I can immediately think of where there’s a significant (~2x) bioavailability difference between plants and animals. Not big enough to make the animal source "more efficient" from a resource use perspective considering the feed conversion still.