Durojaye OA, To SDF, Elliott KEC, Gerard PD and Peebles ED*
Air cell size profile during incubation and its relationship with eggshell temperature (EST) and cumulative percentage egg weight loss (CPEWL) in Ross 708 broiler hatching eggs was determined. On each of the 4 middle tray levels of a single-stage incubator, 72 eggs were weighed and set. On each level, 7 different eggs were randomly selected at the same time each d between 3 and 12 days of incubation (doi) to measure egg weight, EST, air cell depth (ACD), total egg volume, and air cell volume (ACV). Daily CPEWL and relative ACV (RACV; percentage of total egg volume) of each egg was calculated. Mean daily CPEWL (R2=0.8687), EST (R2=0.4757), ACD (R2=0.7106), ACV (R2=0.8424) and RACV (R2=0.8447) increased, whereas egg weight (R2=0.2722) decreased between 3 and 12 doi. Between 3 and 12 doi, ACD increased by 0.43 cm, which averaged approximately 0.048 cm per day. Mean ACD and ACV, respectively, increased from 0.87 cm and 0.97 mL on 3 doi to 1.30 cm and 4.53 mL on 12 doi. Moreover, across 3 and 12 doi, CPEWL was positively correlated with ACD, ACV, and RACV, and EST was positively correlated with RACV. Within doi, CPEWL was observed to have a significant positive correlation with ACD from 3 to 5 and 7 to 12 doi, and with ACV and RACV from 4 to 12 doi. To maintain their close proximity to the inner shell membrane, the dimensions of temperature sensing devices and the timing of their insertion into the air cells of broiler hatching eggs should be commensurate with the described changes in ACD and ACV between 3 and 12 doi. Furthermore, the relationships described between CPEWL, EST, and air cell size (ACD, ACV, and RACV) confirm that CPEWL is the major factor in determining air cell size profile throughout incubation, and that the additional influence of EST can become manifest through its effect on RACV.
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