A trial was set up by the NC State University in the US to determine the effect of egg warm-up temperature and duration of warm-up prior to incubation upon embryo growth.
A series of 9 trials were conducted. Only fresh eggs were used from a collection 1 hour after the initial collection of the day from a Cobb 500 flock for trials 1-6 and from a Heritage flock for trials 7-9.
Immediately after collection eggs were stored for 3 days at 18.3°C. After the 3 days of storage, the eggs were randomly assigned to 6 groups of 15 eggs each. Two groups were placed in one of 3 force draft incubators for warm up temperature treatment maintained at 18.3, 23.9 or 29.4°C. Within each warm up temperature there were 2 duration groups, one group was warmed for 8 hours and the other for 12 hours (trials 1-4), in trial 5-6 eggs were warmed for 12 or 16 hours and in trials 7-9, eggs were warmed for either 12 or 20 hours. After warm up, the eggs were incubated for 36 hours at 37.5°C.
Four viable embryos from each treatment group (temp and duration) were removed from the egg and examined under a microscope for the number of somites present. Only embryos that could be examined within a one hour time period were used.
There was a significant difference in the number of somites for duration of warm up (10.17 versus 11.93 in trials 1 to 4 but no effect by warm up temperature. In trials 5 and 6 there was no effect due to warm up temperature on the number of somites. Trial 6 demonstrated a significant effect due to duration of warm up (10.75 versus 11.58) and trial 5 approached significance for duration. Trials 7 to 9 where the Heritage broiler eggs were used, the embryos exhibited no significant effect due to duration, but in 2 of the 3 trials there was a significant effect due to temperature during warm up.
NC State University reports that the evidence of the trials suggests that there can be effects of either duration of warm up prior to incubation as well as the warm up temperature but that it may also be related to strain of the broiler.