I understand that Toady and Three Two have just implemented the grazing/pasture feature a few releases ago and probably have not included everything they wanted into this new area; I could not, however, find more detailed information about new add-ons for this features and thus would like to suggest an improvement.
As of the current release (0.31.25), purchasing grazing animals for use in pastures is almost always not recommended because the net utility gained does not equal the substantial disadvantages that coming with grazing. While using grazing animals provide you with a new source of relatively high-quality food (i.e. milk and cheeses), the disadvantages are significant: (1) your animals must graze outdoor (for most of the early- and mid- game) where Fun is readily available, (2) food produced from grazing animals are, on average, less efficient per value, than other available means, and (3) your dwarves have to exposed themselves to Fun every time they venture outside.
As such, one way to better balance the advantages and disadvantages of using grazing animals is to introduce the concept of animal droppings, specifically allowing the player to collect animal droppings from grazing animals in order to use in the production of fuel. There is a strong historical basis for this type of industry; Native Americans and the pioneers coming after them often collected animal droppings (buffalo chips!), sun-dried into a brick-like form, and used it as a source of fuel. In-game, you might allow dwarves to collect animal droppings and drop them off in a compost (built on a tile requiring OUTSIDE and LIGHT properties). After a certain period of time (varying by the temperature of the biome), the collected droppings would develop into dried, solid material that could be used in place of charcoal or coke. Of course, certain factors would not to be adjusted to account for realism and gameplay balance: animals produce different quantities of compost-ready material relative to their size (elephants could be useful again!), "animal bars" produced from the compost might be less efficient than charcoal or coke to account for their relatively ease-of-production, etc.
Thoughts appreciated as always.