Genetic variation in the feeding efficiency of maize genotypes evaluated from experiments with fattening bulls

— Genetic variation in the feeding efficiency of maize genotypes was evaluated from experiments with fatten- ing bulls. Maize genotypes were chosen to represent a range of digestibilities from previous experiments with standard sheep. The variation in daily gains observed when bulls were fattened with hybrids of low digestibilities or high energy values was about 65 g per animal. When fed to bulls, the voluntary silage maize intake could be different in hybrids with similar energy values. Thus, differences in feeding efficiency of maize hybrids were related both to digestibility and ingestibility, especially for late hybrids among which variations for digestibility appeared lower than among earlier ones. As observed with brown-midrib (bm3) hybrids, genotypes with a greater digestibility and/or ingestibility might allow a reduced supply of energy-giving concentrates in the diet. Bull performances appeared to be related to both sheep digestibility estimates and the enzymatic solubility values of the whole plants, but this link could have been overestimated due to the similarity among hybrids in grain and dry-matter content of the silages. For maize breeders, the prediction of hybrid efficiency in cattle rearing must include both digestibility and ingestibility factors. Because the stover digestibility and the starch content can be predicted reliably with the use of NIRS (near infrared reflectance spectroscopy) calibra- tion, the most important challenge for maize breeders in the future will probably be the development of a criterion for the intake prediction.