GENETIC-VARIATION IN THE FEEDING EFFICIENCY OF MAIZE GENOTYPES EVALUATED FROM EXPERIMENTS WITH DAIRY-COWS

Genetic variation in the feeding efficiency of maize genotypes was evaluated from experiments with dairy cows. Maize genotypes were chosen to represent a range of digestibilities from previous experiments with standard sheep. The variation in milk yield observed with dairy cows fed genotypes with low or high digestibilities or energy values was about 1.0-2.0 kg per animal per day. Moreover, the range of variation in body weight was about 10-30 kg during the 3 months of the experiments. Hybrids with similar energy values had a similar effect on milk yield, but the intake of each hybrid could be very different when they were fed to dairy cows, even if no difference in intake had been observed in sheep. The higher silage maize intake of 'DK265' was mostly converted into a body weight gain rather than an increased milk yield. probably because the milk yield potential of the animals was soon reached. It appeared that those hybrids whose predicted energy value from sheep measurements was low led to relatively low performances in cows. Dairy cow performances also appeared to be related to the enzymatic solubility values of the whole plants. For maize breeders. the prediction of hybrid efficiency in dairy cow rearing must include digestibility and ingestibility factors. The most important challenge for maize breeders now will probably be the adjustment of a criterion for predicting intake because the stover digestibility and the starch content can be predicted reliably with the use of NIRS calibrations.