Discussion
The higher body weight of Growth strain in this study is
in contrast to that found in the first trial from this
laboratory (Cerrate et al., 2007a) in which the Yield strain
had superior growth rate. However, it should be again
mentioned that birds from the two different strains were
obtained from breeder flocks of two different ages,
obtained from two different hatcheries, transported
different distances to the research facility and held
different times before being placed on feed. It is
important to note, however, that the differences in growth
rate were reflected in the choice of diets by the two
strains. Birds of the Growth strain were significantly
heavier and had a significantly higher feed intake with a
concomitantly higher intake of both energy and protein.
However, the efficiency of utilization of both energy and
protein did not differ significantly between the two
strains. It appears that the growth rate was a primary
determinant in the selection of choice diets. Only for the
last period, 42-49 days of age, was the feed conversion
of YIELD strain better than that of Growth strain. It has
been shown that lean strains had better feed conversion
than did fat strains (Mastika and Cumming, 1981;
Leclercq and Guy, 1991).
The lack of difference in body weights and feed
conversion between birds fed choice diets and control
diets found in this study is in agreement with previous