Supplementary plant extracts did not change
dietary ME (P > 0.05) but improved (P < 0.05) dietary
NE by reducing the heat increment (P < 0.05) per kilogram
feed intake. Feeding phytogenics improved (P <
0.05) total carcass energy retention and the efficiency
of dietary ME for carcass energy retention. The number
of interactions between type of diet and supplementary
phytogenic feed additive suggest that the chemical
composition and the energy to protein ratio of the diet
may influence the efficiency of phytogenics when fed
to chickens. The experiment showed that although supplementary
phytogenic additives did not affect dietary
ME, they caused a significant improvement in the utilization
of dietary energy for carcass energy retention but
this did not always relate to growth performance.