The objective of this study was to determine if the bore diameter of needles used for in ovo injection of amino acids (AA) would affect subsequent chick hatchability. In Experiment 1, needles of different bore diameter were inserted into the egg. In Experiment 2, needles of different bore diameter were used to administer an AA solution that is identical to the AA pattern of the whole egg protein. In both experiments, 27, 24, 22, 20, and 18 gauge needles were tested. Needles were inserted to a depth of 13 mm in both experiments. Non-injected eggs were served as control in each experiment. Needle bore diameter did not affect (P&lt
0.05) hatchability or body weight (BW) of hatched chicks in either experiment. © 2002, Japan Poultry Science Association. All rights reserved.