Changes During Incubation Within Double-Yolked Duck (Anas platyrhynchos domesticus) Eggs: Yolk Position, Mortality, Hatchability and the Importance of an Optimal Egg Size

Double-yolked (DY) and single-yolked (SY) duck eggs (n = 1318 for both) were candled and weighed on Days (d) 2, 8, 12, 15, 19, 22 and 25 of incubation and yolk/embryo position was recorded on d2, d8 and at post-mortem. From d8 only eggs with live fertile yolk(s) remained in the incubator. On d2, 99.39% of yolks in DY eggs were in the adjacent position and by d8 yolk positions changed to parallel position in DY1F (one fertile yolk) and DY2F (two fertile yolks) eggs, 14.1 and 88.62%, respectively (p<0.001). Thus yolk position is associated with yolk fertility. In eggs with two infertile yolks yolk position remained adjacent in 88.21% of the eggs. Early (d1-d8), mid (d9-d21) and late (>d22) embryonic mortality was significantly higher in DY compared to SY eggs (p<0.001). Early mortality was higher in DY1F eggs (31.58, vs. 12.03% DY2F eggs; p<0.001). Late mortality was higher in DY2F eggs (70.38, vs. 51.03% DY1F eggs; p<0.001). Hatchability of fertile SY eggs was 87.2% (1001/1148). Single ducklings hatched from 11 of 437 DY1F eggs (2.52%) and from two of 449 DY2F eggs (0.44%). The egg weight of hatched DY eggs tended towards the SY egg norm suggesting an optimal DY egg size and associated yolk volume for the successful production of viable ducklings.