Benefits and limitations of the genetic selection of broilers for rapid growth

Abstract

Consequences of broiler selection for rapid growth are examined using a calculation model based on a 6 equations system developed in a previous paper (Carré and Méda 2015). With a 2.5 kg slaughter body weight objective, this model predicts that one day reduction in the rearing period linearly reduces the feed conversion ratio by a value ranging from 0.031 to 0.036. Thus, according to this calculation, genetic selection for increased growth rate is by far the most efficient way to improve feed efficiency. Also, feed saving associated with future increased growth rate will affect both energy and protein feed sources. However, the anticipated protein saving effect will come mainly from increased utilization of pure amino acids, not from improved growth rate. In modern broiler lines, the reduction in relative organ sizes resulting from the increased meat yield was at the opposite of what it should be expected when considering an increased feed intake relative to body weight. This paradox can be explained in modern broilers either by an improved efficiency of organs or by a disappearance of some functions, as assessed by previous studies on the size and efficiency of the digestive tract performed in commercial broilers and in the experimental genetic broiler lines D+ and D- divergently selected for digestion efficiency.