The term respiration is used here in a broad sense that is equivalent to oxidative metabolism, or to the liberation of energy for all aspects of body maintenance such as heat production and muscular work. However, in practice, it is difficult to use the relationship between heat loss and rate of growth to assess productivity. Bulls, for example, exhibit a high heat loss coupled with a rapid growth rate. In this case, the energy lost as heat is more than offset by the greater efficiency of lean meat deposition relative to fat deposition. If you don't eat, you don't grow, as many generations of parents have yelled at their kids across the dinner table.
Farm animals have considerable control over the amount and the nature of the things that they eat.
In many practical and experimental situations this behavior may be a primary factor in the regulation of growth. Control may be passive, as in the increased energy cost of locomotion as an animal grows heavier. Active controlling elements may involve hypothalamic feed-back circuits. Roughage Ruminants consume a considerable volume of roughage, and the rumen may be filled before energy requirements are satisfied. Normally, however, feeding behavior changes to accomodate differences in the energy content of the feed.