Results and Discussion
Calculated and analyzed values for CP and amino acid content are shown in Table 2. Analyzed CP values for all diets were in good agreement with the calculated values. Analyzed levels of all supplemental amino acids were all in close agreement with the calculated values.The amino acid content in all diets was higher than the NRC (1994) recommendation for essential amino acids.
Reduction of CP level in the diets had a significant influence on the live performance of male broilers (Table3; Fig. 1). As noted in the previous results from our laboratory, a reduction in the dietary crude protein to levels lower than 22% resulted in a significant reduction performance when added to diets with 16 or 18% CP.in the BW gain and an increase in the FCR even though The FCR of birds fed the 18% CP diet supplemented the low CP diets were formulated to provide a minimum with the EAA mixture did not differ significantly from that of 110% of NRC (1994) amino acid recommendations. of birds fed the 22% CP diet but was significantly less
Addition of a mixture of EAA to bring total dietary levels than that of birds fed the diet with 24% CP. The equal to that of the 22% CP diet improved performance improvement in FCR of chicks fed the 16% CP diet slightly when added to the 20% CP diet and significantly supplemented with the EAA mixture was equal to that when added to diets with 16 or 18% CP. Chicks fed the obtained on the 18% CP diet but was less than that EAA-supplemented 18 and 20% CP diets did not differ obtained on diets with 22 or 24% CP. significantly in BW from those fed the 22% CP diet but Addition of the NEAA mixture to provide N equivalent to were significantly lighter than those fed the 24% CP that from the EAA mixture had variable results. There diets. Addition of the mixture of NEAA to equal the N was no apparent benefit observed when added to diets
content of the EAA mixture also improved the BW of with 20% CP but a significant improvement when added chicks fed the 20% and 16% CP diets but had no effect to diets with 18% CP. Addition to the diet with 16% CP on BW of chicks fed the 18% CP diet. resulted in a numerical but nonsignificant improvement Reduction in dietary CP had a significant effect on feed in FCR.
conversion by male broilers (Table 3; Fig. 2). Decreasing The nitrogen excretion significantly decreased as the CP the dietary CP resulted in significant increases in FCR at levels declined, but was increased by the addition of each reduction in dietary CP level. Addition of a mixture mixtures of EAA or NEAA at each level of CP (Table 3;of EAA to bring total dietary levels equal to that provided Fig. 3). The increased N excretion that resulted from by the 22% diet had no significant effect when added to addition of the mixtures of EAA or NEAA suggests that the diet with 20% CP but significantly improved the supplements were not totally used to support protein
accretion but were being excreted. This research suggests that the growth performance
These results indicate that problems encountered in may be maintained when dietary protein accretion but were being excreted. This research suggests that the growth performance
These results indicate that problems encountered in may be maintained when dietary protein levels are
diets with low levels of CP might be overcome through moderately reduced and diets are supplemented with
more EAA supplementations as we observed at the 20% the EAA (Daghir, 1983; Han et al., 1992; Morris et al.,
CP diet and the 18% CP diet. This may also indicate that 1992; Deschepper and DeGroote, 1995). However, a
the NRC (1994) recommendations for some EAA are not further reduction in CP levels still has a detrimental
sufficient when the CP levels in diets decrease. effect on the performance that cannot be overcome by
However, adding sufficient amounts of essential amino simple additions of EAA or NEAA mixtures. Further
acids to the 16% CP diet and bringing essential amino experiments should be carried out to examine the
acids in the diet up to content same as the 22% CP diet possibility of more varieties and quantities of the EAA
did not totally overcome the adverse effects of the low CP supplementations to the diet low in CP to improve the
diet. In a like manner, the addition of an equivalent performance of chicks fed the low CP diet.
amount of nitrogen in the form of a mixture of NEAA had Stucki and Harper (1961) pointed out the importance of
limited effects compared with the EAA supplementation. providing NEAA in diets with low crude protein.