effect of digestible protein and sulfur amino acids in starter diet on performance and small intestinal (jejunum) morphology of broilers

introduction protein is an essential constituent of all tissues of animal body and has major effect on growth performance of the bird. a better understanding of the nutritional requirements of amino acids allows a more precise nutrition, offering the possibility for the formulator to optimize the requirement of at least minimum levels of crude protein by essential amino acids requirements, generating better result and lower costs for the producer. methionine + cystine (total sulfur amino acid = tssa) perform a number of functions in enzyme reactions and protein synthesis. methionine is an essential amino acid for poultry and has an important role as a precursor of cystine. methionine is usually the first limiting amino acid in most of the practical diets for broiler chicken. the efficiency of utilization of dietary nutrients partly depends on the development of the gastro intestinal tract. material and methods a 2×3 factorial arrangement in a crd experiment was conducted to study the effect of digestible protein (dp) and sulfur amino acids (dsaa) during the starter period on performance and small intestinal (jejunum) villous morphology. a total number of 300 day-old ross 308 male broiler chicks were randomly distributed to 30 groups with 10 chicks each. treatments consisted of two dietary levels of dp (19.5 and 21.5%) and three dietary levels of dsaa (0.94, 1.02 and 1.1%) that were fed for 10 days. for each group and treatment, feed intake (fi), weight gain (wg) and feed conversion ratio (fcr) were calculated and all the data were statistically analyzed by the sas software. results and discussions the effects of different levels of protein and digestible sulfur amino acids on the mean feed intake, feed conversion ratio and daily weight gain are shown in the table 3. increase in the percentage of digestible sulfur amino acids, increased the levels of feed intake and feed conversion ratio in the starter period but, had no effect on the wg. adding the dsaa amount, higher than the recommended levels by ross in the starter period, had no significant increase in the wg, fi and fcr. increasing dsaa in the starter diet, although did not improve the fcr, but significantly increased daily weight gain and feed intake at the end of the period. with a decrease of 10 percent in digestible protein of the starter diet and its counter-action with digestible sulfur amino acids had no effect on wg, fi and fcr in any experimental periods. by taking the use of the diets of 20% crude protein (cp) and 0.641% and 0.926% of total sulfur amino acids (tsaa) or the 22% of cp and 0.705% and 0.926% of tsaa, no weight gain difference was observed from 1 to 7 days of age. also, a 2% reduction of cp in diet of the starter period was not effective on the wg. the results of the present experiment showed that in the starter diets containing 3025 kcal/kg of metabolism energy, the levels of the digestible protein could be increased 20 gr per every kg of diet, without observing any negative effect on the performance of the broilers and in this situation extra amino acids are added to the diet. results of the effects of different levels of the digestible protein and digestible sulfur amino acids on the carcass parts and the gastro intestinal tract are presented in the table 4. increasing the dsaa, had no significant effect on carcass parts and relative weight of the gastro intestinal tract in the day 42, but the abdominal fat decreased (p<0.05). similar levels for the methionine are needed to improve the output of the diet and the breast yield among the range of 3 to 6 weeks age. the morphology of the jejunum of the broilers of 10 days age, are shown in the table 5. with an increase of 8.5% in dsaa of the diet, length and width of the villous of the jejunum were increased in the day 10. by decreasing 10% of the digestible protein of the starter diet, muscle thickness of the jejunum was lessen in the age of 10 days. in the starter period, the levels of the digestible lysine had no effect on the length of the duodenum and jejunum villous. relative lengths of the gastro intestinal tracts are accessible in table 6. conclusion increasing the percentage of the digestible sulfur amino acids in the starter diet, improved the fi and fcr but had no effect on the wg. increasing the dsaa in the starter period, daily weight gain and feed intake were significantly increased in the final total periods but not for the fcr. 10% decrease in the dp and it’s interaction with digestible sulfur amino acids of the starter diet, had no effect on any of the parameters in any periods. with an 8.5% increase in dsaa of the starter diet, the abdominal fat in the 42 days age was decreased. 10% decrease in digestible protein of the starter diet, decreased the muscle thickness in the age of 10 days.