Table 1.

Summary of the effects studied regarding in ovo injections in chicken embryos at various locations and times of incubation and biologics supplemented.

Biologics injected	Reference	Stage of incubationa	Location of injection	Results
Carbohydrates	(51, 66, 113–115)	Late stage	Amniotic fluid	Trophic effects on small intestine and effects on goblet cell activity; effects on embryonic metabolism and body weight
Amino acids	(116–118)	Late and early stage	Amniotic fluid, yolk sac, air cell, site not specified (needle length and narrow/broad end of egg given)	Effects on chick-to-egg ratio, body weight, bursal weight, and thymus weight; effects on body weight in relation to location and day of injection; effects feed intake, feed conversation ratio, and immune response
Hormones	(119–121)	Late and early stage	Albumen	Effect on muscle content; effects on body weight, skeletal growth, feed efficiencies, and adipose tissue development
Prebiotics, probiotics, synbiotics	(122–125)	Early stage	Air cell, amnion	Effects on muscle fibers and histology; effects on Salmonella colonization; effect on final body weight gain and pancreatic enzyme activity; effect on number of bifidobacteria in feces
Proteins (antibodies)	(126, 127)	Late and early stage	Yolk sac, albumen, amniotic fluid	Effects on body weight and muscle mass varied among injection locations; effects on antibiotic residue detection
Immunostimulants	(128–130)	Late stage	Amniotic fluid	Effects on in vitro bactericidal activity of heterophils and protection against Salmonella invasion; effect on macrophage and antibody response

^aDay of incubation, early stage = 0–12 days of incubation; late stage = 13–21 days of incubation; see reference for exact day of incubation.