For the low-input system, it is inadequate to think
of genetic improvement only in terms of increases
in output traits, such as body weight, milk or
egg production, or fleece weight. Efficiency is
also a key criterion. Unfortunately, very little
is known about the genetic improvement of
intrinsic efficiency. Increased efficiency is usually
measured in terms of increased gross efficiency.
The increased gross efficiency observed in highproducing
animals results from the fact that a
lower proportion of the animals’ nutrient intake
is used for maintenance, and a correspondingly