This study was performed to evaluate the performance of broiler chicks fed
diets containing different combinations of plant protein sources during the period from
17 to 45 days of age. Five isoenergetic-isonitrogenous diets (ME of about 3000
kcal/kg and CP of about 19%) were formulated and used. Soybean meal (SSM) was
used to provide the main plant protein in the control diet. Equal amounts of protein of
cottonseed meal (CSM) and corn gluten meal (CGM) were used to replace 25, 50, 75
or 100% of SBM protein in the corn-SSM control diet. Two hundred and ten 17-day-
old unsexed broiler chicks were randomly distributed into five equal experimental
groups, each with 6 equal replications, kept at the rearing batteries and fed ad libitum
their respective mash experimental diets. The growth performance criteria, including
live body weight, weight gain, feed intake and feed conversion, were measured
weekly and for the entire experimental period. Total mortality and net profit per kg gain
were also measured. Nutrient digestibilities of the experimental diets were determined
when the birds were 35 days of age. The proximate analyses for representative
samples of the experimental diets and excreta were undertaken. Also, crude protein
and crude fiber contents of CSM were determined. At the end of study, certain criteria
of carcass yield and components and some blood constituents (blood hemoglobin
concentrations and serum levels of glucose, total protein, total lipids and cholesterol
as well as activities of serum transaminases: AST and AL T) were quantified. The most important results, for the entire experimental period, can be
summarized as follows: +- Dietary treatments had no significant effects on either the
percentages of carcass yield and components or blood constituents, except blood
hemoglobin concentration which decreased significantly in the SSM-free diet group
compared with that of the control group. t Dietary treatments did not adversely affect
feed intake, feed conversion, net profit per unit of gain or digestibility coefficients of
nutrients when up to 50% of SSM protein was replaced by CSM plus CGM. ~
Replacing 75 or 100% of SSM protein with CSM plus CGM resulted in significant
decreases in criteria of growth, feed conversion, digestibilities of dry matter, organic
matter, crude protein, ether extract and nitrogen free extract and percentages of
nitrogen retention, compared with the corresponding values for the control group. In conclusion, when SSM represents the main protein source in plant protein
broiler diets, taking the practical, nutritional and economic aspects into account, up to
50% of SSM protein can safely be replaced by equal amounts of protein from both
CSM and CGM. The diets also should be well balanced in terms of their contents of all
nutrients, particularly, the most limiting amino acids.