Effects of hatching egg storage duration and warming rate from storage to incubation temperature on morphological broiler embryo development

Hatching egg storage affects the development and survival of broiler embryos. Storage for longer than 7 d is associated with decreased hatchability, delayed hatching, and lower day-old chick quality. These negative effects may be mitigated by the rate at which eggs are warmed from storage temperature (18°C) to incubation temperature (37.8°C), which is referred to as the 'warming rate'. The current study investigated effects of broiler egg storage duration in interaction with warming rate on morphological embryo development and survival, and how albumen and yolk pH are affected. An experiment with a 2 × 3 factorial arrangement, testing 2 storage durations (4 and 14 d) and 3 warming rates (10, 24, and 144 h), was conducted. During 14 d of storage, embryos advanced morphologically, but during warming and incubation, these embryos lagged behind compared to those stored for 4 d. This might be due to the larger difference between albumen and yolk pH after 14 d of storage, potentially explaining the shorter chicks at hatch compared to a 4 d of storage (19.5 vs 19.6 cm; P = 0.04). A 24 h and 144 h warming rate allowed the embryo time to develop before reaching incubation temperature, without affecting growth during incubation. A 144 h warming rate resulted in longer chicks at hatch (19.6 vs 19.5 cm; P = 0.04) and a shorter incubation duration (77 h; P < 0.01), compared to a 10 h warming rate. After 4 d of storage, hatchability increased from 93.6 % for the 10 h warming rate to 96.0 % following a 144 h warming rate (P = 0.04). After 14 d of storage, hatchability was similar for all warming rates. Incubation duration, however, increased for the 10 h and 24 h warming rate compared to 4 d of storage (2 and 9 h respectively; P < 0.01), but not for the 144 h warming rate. The absence of a hatch delay suggests that a warming rate of 144 h may have compensated for the developmental delay typically associated with 14 d of egg storage.