Aim: This study aimed to examine the effect of dietary Spirogyra jaoensis in starter feed on growth performance, pectoralis muscle (PM) growth, and small intestine morphology of broiler chickens. Materials and Methods: One hundred twenty one-day-old Cobb-500 broilers (body weight 46±2.6 g) were divided into four equal groups with 3 replicates in each group and given basal feed supplemented with dried S. jaoensis at doses of 0%, 0.5%, 1%, or 2%. The treatment was carried out until the chickens were 18 days old to examine growth of broiler chicks at starter period (8-21 days old). Results: Supplementation with S. jaoensis at doses of 0.5% and 1% resulted in increased weight and improved feed conversion ratio compared to the control group. At the end of treatment, chickens fed with 0.5% and 1% S. jaoensis weighed 428.3±47.8 g and 426.9±31.8 g, respectively, and were significantly heavier than the control group (373.1±44.1 g). Furthermore, parameters related to PM growth and small intestine morphology of chickens supplemented with 0.5% S. jaoensis in basal feed were improved compared to the control group. Conclusion: The results of this research indicate that S. jaoensis at a dose of 0.5% improves growth performance, PM growth, and small intestine morphology in broiler chickens. Keywords: broiler chicken, feed supplement, pectoralis muscle growth, small intestine, Spirogyra jaoensis.

<p><span lang="EN-US">The needs for chicken meat have been dominated by meat from exotic broilers (bred from imported parent). The potential of local broilers chicken in Indonesia is expected to be able to provide the meat for national needs for chicken meat. The objective of this research was to determine the day-old-chick (DOC) phenotypic characteristics of chickens in Indonesia that have the potential as broilers. The phenotypic characteristics are in the form of body morphometry, visceral organ weight and small intestinal histo-morphology. The chickens used were the DOC type of exotic Broiler, Kampung, exotic male Layer, KUB-1 and Pelung. A total of 125 chickens consisting of 25 chickens of each strain at posthatched age were observed for its body morphometry and its visceral organ weight, and small intestinal histo-morphology. The observed data were then analyzed by similarity analysis using MVSP 3.22 to create a dendogram with the Unweighted Pair Group with Aritmetic Average (UPGMA) method. Results showed that there were 2 different clusters from the level of similarity in their characteristics. Exotic broilers had 94.65% similarity to male exotic layer chicken and 92.26% to pelung chicken, while Kampung chickens had 90.16% similarity to KUB-1Chicken. In conclusion, it is indicated that the level of similarity of the phenotypic characteristics of pelung chickens were close to the type of exotic broiler and male exotic layer chicken. This level of similarity lead  to the expectation that pelung chickens potential to be a candidate for meat-type of local chicken.</span></p>