Abstract: The aim of this study was to investigate whether antibodies specific to growth hormone receptor (GHR) extracellular domain (ECD) could activate or inhibit GHR signal transduction, and whether the antibodies could be used to regulate animal growth performance. Firstly, an N-terminal 120-amino acid residue chicken GHR ECD was prepared by recombinant technology, and was used as the antigen to immunize growing pullets. Anti-GHR antibody titres rapidly increasedafter the primary immunization in both high and low groups (P<0.01), and were similar in both GHR ECD immunized groups, but were significantly higher than the non-specific levels in the control group throughout the experiment (P<0.05). Immunization against GHR ECD was significantly (P<0.01) inhibited live weight gain in both high and low group pullets, that the live weights were already lower only 30 d following the primary immunization than that of control group (P<0.05). Following suppression of weight gain, GHR ECD immunized groups also exhibited significant (P<0.05) depression in daily feed intake at the later stage of the experiment. Upon slaughter, the control pullets had higher carcass weight, slaughter rate, semi-enviseration and enviseration percentages, and higher abdominal fat ratio than did the high and low groups. These results demonstrated that immunization against GHR ECD inhibited chicken growth, which implied the antibodies to GHR exhibited a GHR signal transduction blockade effect. The results also implied that immunization against GHR ECD would be unlikely to be used to promote animal growth, but might be applicable to restrict animal growth as in the case of breeder pullet rearing.

Key words: chicken; immunization; GHR; growth; feed intake