Observations of turkey eggs stored up to 27 days and incubated for 8 days: embryo developmental stage and weight differences and the differentiation of fertilized from unfertilized germinal discs

For logistical reasons, egg storage prior to incubation is a growing practice in the commercial turkey industry. Yet the consequence of increasing egg storage over 7 d is a progressive increase in embryo mortality. The objective of this study was to provide the information necessary to differentiate an early dead embryo from an unfertilized egg after 8 days of incubation (DOI). Five groups of eggs each from inseminated and virgin hens were stored for progressively increasing periods of time (5-d or less, 6 to 10 d, 11 to15 d, 16 to 20 d, and 21 to 27 d) and incubated. At 8 DOI, eggs were examined and the stage of development (Hamburger and Hamilton, 1951) and embryo weights in normally developed eggs were determined. There was a significant negative correlation between the stage of development and embryo weight with increasing storage periods. All remaining eggs from the inseminated and virgin hens were broken-out and the appearance of the yolk and the fertilized and unfertilized germinal discs examined. The yolks of both hen groups with unfertilized ova maintained a homogeneous uniform yellow-orange color. In contrast, yolks of ova that had been fertilized, with or without early-dead embryos, and yolks from virgin hens that showed evidence of parthenogenetic development (3%) had a heterogeneous appearance. Using fluorescence microscopy, the heterogeneous appearance was due to sheets of aberrant cells and less frequently dispersed cells and folds of the perivitelline layer. It was concluded that clear egg breakouts need to be performed to more accurately assess the impact of egg storage on embryonic mortality. Furthermore, such breakouts should be performed with a high intensity light directed across the surface of the germinal disc to clearly differentiate the subtle differences between an early-dead embryo and an unfertilized germinal disc.