Towards an understanding of the concept of genotype-dietary interaction

The concept of genotype-dietary interaction ha~ considerable bearing on especially two aspects of the beef industry: performance testing of bulls and the matching of most suitable genotypes to particular production systems. With regard to performance testing the results imply that the order of merit between bulls could be altered due to genotype-dietary interaction. Therefore, it is preferable that bulls should be tested within the nutritional environment in which they are kept. With regard to the concept as possibly applicable to production systems, it would appear that some results in the literature need re-evaluation. What is possibly being interpreted as genotype dietary interaction could be a function of inadequate apprehension of the impact of the effects of scaling for size, the multiplicative (curvilinear) nature of growth and the differential size of measurement error with different feeds and feeding levels.