59 Egg albumen and yolk contain amino acids for the developing embryo, however, a large fraction of egg protein consists of antibodies, which the hen produces during the immune response experienced at the time of egg laying (Losch et al . 1986). Under normal circumstances, these immunoglobulins are fully functional at the time of hatch (Brierley and Hemmings 1956). Gluconeogenesis from protein provides glycogen that fuels hatching activities (Klasings 1998). Thus, early provision of nutrients affects immediate embryo survival and disease resistance and also the ultimate attainment of genetic potential. Efforts were made to achieve higher protein synthesis by injecting AA directly into the egg (Ohta et al. 2001, Bhanja et al. 2004b). Accelerated enteric development and improved nutritional status afforded by in ovo feeding improved hatching weight, growth rate (Al-Murrani 1982, Ohta et al. 1999 and Bhanja et al. 2004b), immune responses (Konashi et al. 2000, Bhanja and Mandal 2005), gastro-intestinal development (Uni and Ferket 2004) and meat yield. In ovo supplementation of amino acids during later stage of embryonic development Indian Journal of Animal Sciences 82 (9): 993–998, September 2012 Modulation of post hatch-growth and immunocompetence through in ovo injection of limiting amino acids in broiler chickens SUBRAT K BHANJA 1 , ASIT BARAN MANDAL 2 , SUSHIL K AGARWAL 3 and SAMIR MAJUMDAR 4 Central Avian Research Institute, Izatnagar, Uttar Pradesh 243 122 India Received: 16 November 2010; Accepted: 30 January 2012 ABSTRACT Early post-hatch growth and immunity was assessed through in ovo injection of some critical amino acids on 14 th d of incubation at the broad end of the egg using 25 mm needle. Percent hatchability in lysine (lys) and arginine (arg) injected groups were better than un-injected control group. Threonine (thr) and methionine (met) injected eggs had higher chick weight and chick to egg weight ratio and met and arg injected chicks had higher fourth and seventh week body weight than un–injected control chicks. No significant difference was recorded for FCR of in ovo amino acids injected birds. Met and glycine (gly) injected chicks had higher bursa weight, whereas, those injected with met thr, gly and isoleucine (ile) had higher spleen weight on the day of hatch. Humoral immune response (SRBC titre) was higher in most of the amino acid injected chicks except lys group. Cell mediated immunity (response to PHAP mitogen) was higher in lys, arg, gly and ile injected chicks. The chicks injected with amino acids invariably had higher plasma protein and lower plasma glucose on the day of hatch. It may be concluded that met and thr were critical for the growth of chicken embryo, however, during post–hatch period met and arg played major role. In ovo injected amino acids can also act as immunomodulator but their role in gastrointestinal development needs further research. Key words: Amino acids, Immune response, In ovo injection, Gastrointestinal tract, Growth Present address: 1 Senior Scientist, 3 Head, 4 Principal Scientist, Poultry Housing and Management, (subratcari@gmail.com); 2 Principal Scientist, Division of Avian Nutrition and Feed Technology (abmcari@rediffmail.com). (in ovo feeding) may spare those antibodies from utilization as protein source during embryonic and neonate stages. The present investigation was aimed to study the effect of in ovo injection of some critical amino acids on embryonic and post– hatch growth performance, immune response and development of digestive organs in broiler chickens. MATERIALS AND METHODS In ovo injection: Standard size fertile eggs (800), collected from a dam line of a coloured broiler strain, were weighed and distributed into 8 treatment groups– 25 mg each of limiting amino acids viz. lysine (lys), methionine (met), threonine (thr), arginine (arg), glycine (Gly) and isoleucine (ile) dissolved in 0.5 ml of sterile water, a sham control (0.5 ml sterile water) and un- injected control. The treatment solutions or sham control were injected into the yolk of the 14-day-old embryo, through a pinhole made at the broad end of the egg, using a 24G hypodermic needle (25 mm long) as per Bhanja et al. (2004a). Prior to in ovo injection the injectants were warmed to 30° C. The procedure was carried out under a laminar flow system and the pinhole site was sealed with sterile paraffin wax immediately, and eggs were returned to the incubator. On 18 th day of incubation the eggs were transferred to a hatcher and placed in pedigree hatching