pH Changes in Egg Compartments During Embryo Development in Broiler Chickens

Broiler chickens spend one third of their lives developing inside an egg. Hence, understanding and optimising the in ovo environment is fundamental. The pH of body fluids is tightly regulated to maintain critical physiological functions such as gas exchanges. Enzymes equally have an optimum pH range that determines their efficiency. Changes to these conditions, may impact on the efficiency of O2 transport or enzyme activity. Embryonic development requires a continuous flow of O2 delivery and supply of amino acids and energy through the activity of digestive enzymes. Albumen and yolk provide most nutrients to the embryo during incubation, the amnion provides protection, and the allantois serves as an excreta reservoir (Moran, 2007). It is anticipated that each structure will have a tightly controlled pH during incubation. The current study was developed with the objective to better understand the dynamics of pH changes in egg compartments. We hypothesized that the high respiration rate during embryonic development would be associated with CO2 release and partial depletion of bicarbonate, which is thought to be the main buffer in the egg. Thus, we expected metabolic alkalosis (a decrease in pH) to occur in all main water-rich compartments (albumen, amnion, and allantois).

The pH changes in albumen and yolk, were measured using a laboratory pH meter (HANNA instruments, Model HI98163) on embryonic days (E) 0 (T1), E3 (T2), E6 (T3), E9 (T4), E12 (T5), E15 (T6), and E17.5 (T7). The pH changes in amnion and allantois were studied on E9 (T4), E12 (T5) and E15 (T6). Data was analysed using ANOVA in R Studio. Significance level was set at P< 0.05.

The results showed higher albumen pH on E0 (9.21, P< 0.05) than in successive days with values in continuous decline to 8.94, 8.31, 8.10, 7.39, and 7.18 on E6, E9, E12, E15 and E17.5, respectively. Albumen pH was negatively correlated with incubation day (P< 0.05) showing maximal negative increments (P< 0.05) between E7 to 9 and E13 to 15. In contrast, yolk pH increased from E0 to 15 with values of 6.67, 7.03, 7.56, 7.73, and 8.046 on E0, E6, E9, E12, and E15, respectively. However, by E17.5 the pH decreased back to 7.734 (P< 0.05). Yolk pH was positively correlated with incubation day (P< 0.05). The pH of amnion decreased over time, being higher (7.64) on E9 than on E12 (7.36) and E15 (6.83) (P< 0.05). Amnion pH showed a negative correlation with incubation day (P< 0.05). Similarly, allantois which had a higher pH at E9 (8.83), decreased over time to 8.16 on E12 and 6.54 on E15. The yolk pH was negatively correlated with the pH of the albumen, amnion, and allantois (P< 0.05), while the pH of amnion, albumen, albumen, and allantois pH were positively correlated (P< 0.05).

During the course of incubation, the pH of water-rich compartments (albumen, allantois, and amnion) decreased, while the pH of the fat-rich compartment (yolk) increased, thus confirming our hypothesis. Evidently, a dynamic homeostasis of metabolic acid-base balance is critical for embryonic respiration and development.

ACKNOWLEDGEMENTS: This study was supported by AgriFutures and Delacon.