Bioenergetics, bioengineering and growth

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Abstract
The effects of conventional and novel methods for the manipulation of growth in meat animals are reviewed within the context of the fundamental laws that determine the biological efficiency of energy conversion. Interspecies comparisons reveal large differences in the energetic efficiency of growth between mammals and birds. The similarity between mammals of different sizes is remarkable, both between and within species, which suggests that manipulation of growth rate per se has little effect on efficiency. The best way to improve the efficiency of growth is to maximize the conversion of metabolizable energy (ME) to lean tissue at all stages of maturation. The principal destination of ME is heat, however thermogenesis linked to essential metabolic functions is resistant to manipulation. It is more profitable to manipulate the partition of retained energy between protein and fat. Whether this is achieved by nutrition, conventional breeding or bioengineering, it is necessary to ensure that it does not compromise the normal health and vigour of the growing animal.