Feed intake (FI) of ruminants is of high interest to study feed efficiency, greenhouse gas emissions and health traits. However, FI is a very expensive trait to record. Here, we investigated the genetic correlations between true average daily feed intake (ADFI) considered either as a continuous or categorical trait, and the correlations between simple predictions of FI based on body weights and growth with true ADFI. ADFI is genetically the same trait whether considered as a continuous or categorical trait. RFI calculated from categorical ADFI was genetically the same trait as RFI calculated from true ADFI. However, estimated ADFI from a simple model accounting for zootechnical traits, although positively correlated with true ADFI, led to reduced genetic correlations between categorical traits and ADFI: a maximum of 25% of misclassification of lambs is expected if qualitative predictions of ADFI or RFI have to be considered in future analyses.