Physiological response of broiler embryos to different incubator temperature profiles and maternal flock age during incubation. 1. Embryonic metabolism and day-old chick quality

Broiler strain, maternal age, and incubation temperature influence embryo metabolism. Hatching eggs were obtained from young (Y; 28 to 34 wk, $\bar{\rm x}$ = 31.2 wk), mid (M; 36 to 45 wk, $\bar{\rm x}$ = 40.5 wk) and old (O; 49 to 54 wk, $\bar{\rm x}$ = 51.4 wk) Ross 708 (n = 88; Experiment 1) and Ross 308 [(n = 45; Experiment 2: (Y; 25 to 34 wk, $\bar{\rm x}$ = 30.5 wk), (M; 35 to 44 wk, $\bar{\rm x}$ = 40.2 wk), and (O; 49 to 54 wk, $\bar{\rm x}$ = 51.6 wk)] breeders. Eggs were stored for 2 to 4 d (18°C, 73% RH), and incubated for 14 d at 37.5°C and 56% RH. At 15 d (E15), 8 fertile eggs per flock age were incubated in individual metabolic chambers at 36.0, 36.5, 37.0, or 37.5°C until E21.5. Each temperature was repeated one additional time. O2 consumption and CO2 production were used to calculate embryonic heat production (EHP). Embryo temperature was measured as eggshell temperature (EST). Initial egg weight was used as a covariate; significance was assessed at P < 0.05. In Ross 708, daily EHP tended to be higher in M and O than Y treatments at E16; EHP of M was higher than Y and O eggs at E18; M and O were higher than O eggs at E19. Incubation at 37.0°C resulted in the highest EHP from E15 to E21, except at E17. Embryos at 37.5°C had reduced EHP beyond E17. Daily EST from E15 to E21 was higher at 37.5 and 37.0°C than at 36.0 and 36.5°C. In Ross 308, daily EST was highest at 37.5°C except at E20. Incubation temperature and EST were highly correlated (R2 = 0.90 to 0.89; P < 0.001). Ross 708 chicks were longer and hatched earlier at 37.0°C than at 36.0 and 37.5°C. EST and EHP increased with incubation temperature in Ross 708. In Ross 308, maternal flock age and incubation temperature did not impact EHP. However, EST was highest at 37.5°C except at E20. Ross 708 was more sensitive to incubation temperature than Ross 308.

Influence of parent flock age on embryonic metabolism in modern turkey strains

The metabolic response of some galliform embryos to embryonic heat production (EHP) and how incubation conditions have been adjusted to prevent overheating of embryos is well established in broiler breeders. However, the daily metabolic status of turkey embryos has not been studied or established in turkey embryos. The objectives of the current research were therefore to determine the respiratory (eggshell conductance, G) and metabolic status (EHP) of 2 modern turkey genetic strains [Hybrid (H) and Nicholas (N)] and 4 parent flock ages [young (Y, 30 wk), peak (P, 34 wk), mature (M, 55 wk), and old (O, 60 wk)] during incubation. To measure G, moisture loss from 15 eggs/genetic strain per flock age and saturated vapor pressure measured between the eggshell and its immediate environment were used. Daily embryonic O(2) consumption and CO(2) production rates were assessed 6 times each day from embryos of eggs (n = 11 eggs/genetic strain per flock age) incubated in individual metabolic chambers and were used to determined daily EHP. Data were analyzed using the mixed model procedure of SAS at P ≤ 0.05. The results showed that the G values (g/d per mmHg) were significantly different for the interaction between genetic strain and parent flock age (H × Y = 17.71, H × P = 17.53, H × M = 19.73, H × O = 26.46, N × Y = 16.70, N × P = 20.96; N × M = 25.47, N × O = 26.05; P = 0.0227). Daily EHP (mW) was higher in embryos from the O flock than in embryos from the Y flock during all days presented except at 8, 25, and 28 d of incubation (4 d: Y = 1.00, P = 0.93, M = 1.60, O = 1.75; 12 d: Y = 19.0, P = 20.0, M = 21.6, O = 23.4; 16 d: Y = 51.7, P = 60.5, M = 65.9, O = 70.8; 20 d: Y = 129, P = 146, M = 144, O = 155; 24 d: Y = 154, P = 188, M = 167, O = 180; 26 d: Y = 169, P = 199, M = 197, O = 230; and 27 d: Y = 231, P = 265, M = 288, O = 307; P < 0.05). The data showed that metabolic differences existed between embryos from flocks of different ages and that embryos from older flocks were metabolizing at a higher rate and could be subject to overheating, which requires further investigation. On the basis of the data, turkey eggs from flocks of different ages should be incubated separately for optimal physiological performance.