Abstract: Male broilers of a commercial strain were grown to 10 d
of age on a common starter diet and then from 11 to 49 days were offered
single diets (control), a choice of starter and finisher diets,
isoenergetic choices between 12 and 24 or 32% Crude Protein (CP) diets and
isoenergetic choices between 15 and 24 or 32% CP diets. Birds fed the
isoenergetic diets varying in protein content had almost similar body
weight, feed intake, energy intake and carcass characteristics as did
birds fed the control diets or the choice of starter and finisher diets.
In general the feed and energy conversions by birds given the choice
between 12 and 24 or 32% CP diets were worse than those of birds given the
other feed systems; however, the protein consumption and conversion by
birds fed the former diets were lower than those of birds fed the latter
diets. There was a marked preference for the low protein diets (12 and 15%
CP) over the high protein diets (24 and 32% CP), but this preference was
reduced when the low protein diets were offered with the 24% CP diet. The
levels of protein selected of the isoenergetic diets varying in protein
content were lower than those of control diets or choice between finisher
and starter diets and declined with age except for the last week of the
experiment, possibly due to feed form variation. Birds given the choice
between 15 and 24 or 32% CP diets had similar performance, except for
slightly better protein conversion but slightly worse energy conversion,
as those fed control diets or given a choice of starter and finisher
diets; even though these choice-fed broilers chose lower protein contents
than did birds fed the other two systems. These data indicate that choice
of isoenergetic diets varying in protein content can be used to determine
protein requirements of broilers, being more effective and efficient with
a narrow range of two protein contents. |