276 Proceeding of the 2 nd International Seminar on Animal Industry | Jakarta, 5-6 July 2012 The Effects of Dietary Energy Sources on Immune Organs of Broilers Exposed to Heat Stress M. Prayuwidayati 1, *, T. Pasaribu 1 , R. Palupi 1 , K. G. Wiryawan 2 , A. Sudarman 2 , & R. Mutia 2 1 Graduate Study Program of Bogor Agricultural University 2 Department of Nutrition and Feed Technology, Faculty of Animal Science, Bogor Agricultural University, Indonesia *e-mail: widayub@gmail.com Abstract The aim of this experiment was to study the effect of palm oil addition as energy source in the ration on the percentage of limfoid gland, thymus gland and bursa fabricius of broilers exposed to heat stress. The research was conducted in Experimental Station, Faculty of Animal Science, Bogor Agricultural University, in November to December 2011. The experiment was conducted in a Completely Randomized Design (CRD) consisting of two treatment rations with three replications. The treatments were as follow: R1 = ration with 22% crude protein and 3050 kcal Metabolism Energy containing 1% palm oil; R2= ration with 22% crude protein and 3050 kcal Metabolism Energy containing 7% palm oil. The parameter observed were limfoid gland percentage, thymus gland percentage and bursa fabriosis percentage. The result of the experiment showed that the addition of palm oil in the ration until 7% DM basis in broiler’ration did not significantly affect the lymphoid organ percentage, thymus gland percentage, and the bursa fabriosis percentage in broilers exposed to heat stress. It could be concluded that addition of palm oil as energy sources in the ration gives similar effect on broilers exposed to heat stess. Keywords: broiler, heat stress, lymphoid organ, thymus gland, and bursa fabriosis Introducton Global clmate change has sgnfcant effects on agrculture producton, ncludng poultry producton. Heat stress s one of bg concern n poultry ndustry, especally n tropcal and sub-tropcal countres. It has been well known that heat stress could reduce the productvty and ncrease the mortalty of the chcken, that wll n turn affects the performance of poultry ndustry. Hgh envronmental temperature could hamper the average daly gan of the chcken, as results of lower appette and feed ntake.