Twenty-four sets of full-sib ram lambs, each born from a different sire, were kept individually in pens and hand-reared from birth up to 50 kg live mass. Feed intake and mass of each lamb were determined every third day. Growth curves [ ln(mass) against ln(cumulative feed intake)] were plotted for each lamb. Three growth phases could be identified. Very low heritabilities (h2) were calculated for feed conversion ratio in the second and third phases whereas the h2 in Phase I was 0.32 ± 0.40. Heritability of average daily gain (ADG), estimated with least squares means and regression methods, was 0.40 and 0.39 in Phase I, 0.68 and 0.48 in Phase II, and 0.26 and 0.18 in Phase III. Heritability of the Kleiber ratio followed the same trend but was generally higher. Only the product-moment correlations between feed conversion, ADG and the Kleiber ratio within the same growth phase, differed significantly from zero (P < 0.01). Genetic and phenotypic correlations between traits over phases, were low and insignificant.
