Effects of chronic hypoxia and protein malnutrition on growth in the developing chick

OBJECTIVE: The purpose of this study was to determine how chronic hypoxia and/or protein malnutrition in ovo affect growth in developing chicks. STUDY DESIGN: Chicken eggs were incubated under normoxic (21% oxygen; n = 30 eggs) or hypoxic (14% oxygen; n = 80 eggs) conditions. Hypoxia was imposed from day 0 (n = 38 eggs), day 10 (n = 22 eggs), or from day 0 to 10 (n = 20 eggs). Protein malnutrition alone (n = 20 eggs) or in combination with hypoxia (n = 24 eggs) was induced by removal of 10% of the estimated total albumin content of the egg. Embryos/chicks were killed and weighed at day 10, 15, or immediately after hatch; organs were removed and weighed. RESULTS: Embryos to which hypoxia was imposed from day 0 weighed less than control embryos at day 10, which stayed the same until hatch (64.67% ± 3.56% egg mass vs 69.36% ± 3.90% [mean ± SD]; P < .05). Malnourished chicks at day 15 and at hatch (63.42% ± 4.28%; P < .05) weighed less than control chicks, as did malnourished plus hypoxia chicks (59.74% ± 3.41%; P < .001). Malnourished plus hypoxia chicks weighed less than malnourished chicks alone (P < .05). Embryos that were hypoxic from day 0 to 10 weighed less than control embryos at day 15 (P < .05), but not at hatch. At hatch, neither hypoxia nor malnutrition decreased crown-rump length. Brain and heart weights were increased in both malnourished groups, but not chicks that were hypoxic from day 0. CONCLUSION: Chick embryos exposed to malnutrition show asymmetric growth restriction with relative "sparing" of the brain and heart. Early growth restriction that was induced by hypoxia from the beginning of incubation is reversed by the restoration of normoxia at mid incubation.