One hundred and twenty unsexed one-day old Muscovy ducklings were
distributed into four equal groups each of 3 replicates (10 birds/replicate). Ducklings
were fed on starter diets during the first 14 days post hatching followed by grower
diets till the end of the experiment. Starter and grower diets differed in energy level
and added Yeast culture (YC) to form 4 dietary treatments being diet 1 (control),
containing adequate-energy levels (approximately 2940 and 3040 kcal ME/kg during
the starter and grower periods, respectively). Diet 2 was as diet 1 but with addition of
YC. Diet 3 has diluted-energy levels (approximately 2700 and 2480 kcal ME/kg during
the starter and grower periods, respectively). Diet 4 was as diet 3 but with addition of
YC. Results indicated that body weight (BW) and body weight gain (BWG) were
decreased during most age intervals by feeding the diluted-energy diet with
insignificant increases occurred with addition of YC, but final BW was still lower
compared to the control. Addition of YC to the adequate-energy diet increased BW
and BWG during the early age but had no effect thereafter. Feed intake (FI) was
increased by feeding the diluted-energy diet with further increase observed with
addition of YC. However, such increases cannot maintain energy intake similar to the
control. Addition of YC to the adequate-energy diet did not affect FI. Ducklings fed en
the diluted-energy diet with Or without YC were less efficient in converting feed into
gain. Addition of YC to the adequate-energy diet improved feed conversion during the
early age but not thereafter. However, dilution of dietary energy either wUh or without
YC and also inclusion of YC in the adequate-energy diet resulted in better effIciency pf..
energy utilization compared to the control. Edible and inedible parts, eviscerated
carcass and visceral and pad fats were decreasedwith feeding. the diluted-energy diet
with further decreases occurred due to addition of YC. Addition of YC to the adequate-
energy diet caused insignificant increase in eviscerated carcass with small decrease
in visceral and pad fats. Decreasing dietary energy had no effect on meat crude
protein, while it decreased its fat. Addition of YC to the adequate-energy diet         significantly decreased meat fat.                                                                             _ It is concluded that diluting dietary energy of Muscovy ducklings achieved
desired reduction in carcass fatness but it decreased carcass yield and negatively affected
economic efficiency. Addition of YC to such diluted diet caused further decrease in
carcass fatness with small increase in carcass yield without improving economic
efficiency. Addition of YC to adequate-energy diet caused a slight increase in carcass
yield with a small decrease in carcass fatness without affecting economic efficiency.