An in ovo injection apparatus capable of injecting a plurality of avian eggs carried by an egg carrier having a leading end and a trailing end, the apparatus comprising: a frame and an injection assembly moveably attached thereto, the injection assembly having a plurality of injection devices, each injection device being configured to inject a respective avian egg when aligned therewith; and an advancement system configured to advance an egg carrier carrying a plurality of avian eggs to the injection assembly for injection thereof, the advancement system comprising: a guide assembly fixed, connected or attached to the frame, configured to receive the egg carrier and provide support thereto during advancement of the egg carrier; a manual advancement device configured to slidingly engage the guide assembly such that the manual advancement device is movable along the guide assembly, the manual advancement device being capable of interacting with the trailing end of the egg carrier to advance the egg carrier to an injection position; and at least one stop positioned to interact with the manual advancement device during advancement of the egg carrier along the guide assembly toward the injection assembly so as to prevent progression of the manual advancement device beneath the injection assembly, thereby locating the egg carrier at the injection position. a frame and an injection assembly moveably attached thereto, the injection assembly having a plurality of injection devices, each injection device being configured to inject a respective avian egg when aligned therewith; and an advancement system configured to advance an egg carrier carrying a plurality of avian eggs to the injection assembly for injection thereof, the advancement system comprising: a guide assembly fixed, connected or attached to the frame, configured to receive the egg carrier and provide support thereto during advancement of the egg carrier; a manual advancement device configured to slidingly engage the guide assembly such that the manual advancement device is movable along the guide assembly, the manual advancement device being capable of interacting with the trailing end of the egg carrier to advance the egg carrier to an injection position; and at least one stop positioned to interact with the manual advancement device during advancement of the egg carrier along the guide assembly toward the injection assembly so as to prevent progression of the manual advancement device beneath the injection assembly, thereby locating the egg carrier at the injection position. a guide assembly fixed, connected or attached to the frame, configured to receive the egg carrier and provide support thereto during advancement of the egg carrier; a manual advancement device configured to slidingly engage the guide assembly such that the manual advancement device is movable along the guide assembly, the manual advancement device being capable of interacting with the trailing end of the egg carrier to advance the egg carrier to an injection position; and at least one stop positioned to interact with the manual advancement device during advancement of the egg carrier along the guide assembly toward the injection assembly so as to prevent progression of the manual advancement device beneath the injection assembly, thereby locating the egg carrier at the injection position.