Menu
Genetic selection of modern broiler chicken strains for increased growth, feed efficiency, and breast meat yield has influenced embryonic development. The consequences of increased metabolic rate in broilers include stunted liver and heart tissues, which could result in metabolic inefficiencies in embryos. To optimize incubation conditions, the effects of maternal flock age on embryo metabolism must be considered. Although the effects of flock age and breeder strain on embryo metabolism have been extensively researched, the interaction of incubation temperature with these factors on the physiological growth of embryos and subsequent impacts on hatchling quality are not well understood. Additionally, the confounding effect of maternal flock age on egg weight cannot be discounted. The objectives of the current research were to evaluate the impact of incubation temperature and maternal flock age on embryonic metabolism, eggshell temperature, and early chick quality within each of Ross 708 and Ross 308 broilers.
Fresh broiler breeder eggs were obtained from a commercial hatchery from each of 3 different parent flock ages: young (Y; 28 to 34 wk), mid (M; 36 to 45 wk), and old (O; 49 to 54 wk of age) Ross 708 (Experiment 1) hens. Eggs were assigned to one of 4 incubation temperature treatments (36.0, 36.5, 37.0 (control), or 37.5°C) from E15 to E21.5. For each replicate in Experiment 1, a total of 11 eggs per each of the 3 flock ages was obtained, weighed, and incubated for 14 d at 37.5°C and 56% RH in a Jamesway AVN incubator. Beginning at E15, fertile eggs (n = 8) from each of the 3 parent flock ages were individually transferred into one of 24 one-liter metabolic chambers placed inside the incubator and air samples were analyzed for O2 and CO2. In Experiment 2, 15 eggs per flock age were obtained from Y (25 to 34 wk), M (35 to 44 wk), and O (49 to 54 wk of age) from Ross 308 breeders as described above. The eggs were collected, weighed, and incubated according to temperature treatments as in Experiment 1. Eggshell conductance was not investigated in Experiment 2. Incubation conditions followed standard commercial hatchery procedures. Proper ventilation was maintained with fresh air by connecting a tube from the incubator damper to the hatchery roof and dampers adjusted when necessary to maintain RH at 56%. For simplicity, the flock ages for both Ross 708 and Ross 308 have been defined as young (Y; 26 to 34 wk), mid (M; 35 to 45 wk), and old (O; 46 to 55 wk). Beginning at 452 h of incubation, the eggs were checked at 6-hour intervals to establish the times each embryo was required to externally pip and hatch. All chicks remained in the metabolic chambers, and after 518 h of incubation, they were removed, weighed, and euthanized. The carcasses were dissected; the residual yolk sacs (RYS) were weighed. In each run, embryonic O2 consumption and CO2 production in each of 24 metabolic chambers were measured by computer-software controlled O2 and CO2 analyzers.
Experiment 1. Ross 708: Chick weight was not different among flock ages; however, chick length was different. The chicks of Y flock age were longer than chicks from M and O flock ages. The external pipping time of embryos prior to hatching was higher in M flock age than Y flock age. The percentages of wet and dry RYS as well as yolk-free body mass (YFBM) were not different among maternal flock ages. The daily embryonic O2 consumption was higher in M embryos compared to O embryos at E19. At E20, M and Y embryos showed higher O2 consumption compared to O embryos; there were no differences at the other embryonic ages. The daily embryonic CO2 production was higher in Y and M embryos compared to O embryos at E20. Average over the 7 d investigated showed that the M embryos had higher O2 consumption from E15 to E21 compared to Y and O embryos. The average and daily EST were not different between maternal flock ages. Chick weight was not affected by incubation temperature. The eggs incubated at 37.0°C from E15 to E21 hatched longer chicks compared to eggs incubated at 37.5°C. The 37.0°C treatment also resulted in shorter external pipping and hatching times compared to all other incubation temperature treatments investigated. The chicks incubated at 36.0°C had the longest hatch time followed by 37.5°C and then 36.5°C groups. Embryos incubated at 37.0 or 37.5°C consumed more O2 from E16 to E17 as compared to those incubated at 36.0 or 36.5°C. Average CO2 production from E15 to E21 was not affected by incubation temperature.
Experiment 2. Ross 308: There was no effect of flock age on chick weight, chick length, external pipping time, or hatching time as well as percent YFBM, wet RYS, or dry RYS. There were no differences in daily O2 consumption nor daily CO2 production and EHP among maternal flock ages from E15 to E21. Similarly, the average O2 consumption and CO2 production were not affected by flock age. There were no differences in daily EHP or EST among maternal flock ages. Chick weight, chick length, external pipping time, and hatching time, and percentage of YFBM and wet and dry RYS were not different among the temperature treatments. There was no difference in daily O2 consumption, daily CO2 production, or EHP among incubation temperature treatments from E15 to E21.
The interaction between maternal flock age and incubation temperature treatment did not affect any of the daily or average parameters measured in either genetic strain.
In conclusion, incubation of Ross 708 embryos appears to be more challenging than Ross 308 embryos because of the more pronounced effects of elevated incubation temperature on embryo metabolism. Incubation at 37.5°C, which is used by most commercial hatcheries, could result in embryonic overheating. The use of EST to monitor metabolism during incubation may assist in adjusting incubation temperature to suit the needs of the embryo.