Interaction between ascites susceptibility and CO(2) during the second half of incubation of two broiler lines: the effect on post-hatch development and ascites mortality.

1. The aim of this study was to investigate if genetic predisposition to ascites interacts with changed incubation conditions, and how this might affect the post-hatch performance and ascites susceptibility. 2. An ascites sensitive (A) and resistant (E) broiler line were incubated under standard or high CO(2) conditions (up to 4%) from embryonic d 10 onwards. After hatch, chicks were exposed to cold from the 15th day of the rearing period to increase the incidence of ascites. 3. The A line had a higher post-hatch body weight from week three, higher blood pCO(2) from d 21, higher haematocrit at d 35 and d 42, and higher plasma corticosterone concentration from d 21 onwards, compared with the E line, regardless of incubation conditions, supporting the given selection criteria. Ascites mortality did not, however, differ between lines. 4. Incubation under high CO(2) conditions during the second half of incubation increased the ascites mortality, decreased body weight from week 4 onwards, affected venous blood pCO(2), decreased blood pO(2) from d 31, increased haematocrit at d 35 and d 42, and lowered the thyroxine and triiodothyronine concentrations at most sampling days. These effects were observed in both lines. The results suggested a metabolic programming of CO(2) incubated chickens which affected ascites susceptibility.

Interaction between ascites susceptibility and CO during the second half of incubation of two broiler lines. Effect on embryonic development and hatching process.

1. Because CO(2) during the second half of incubation is known to influence air cell and blood gases, and embryo development, it is postulated that post-hatch development and ascites sensitivity could also be influenced. 2. An ascites susceptible (A) and an ascites resistant (E) broiler line were incubated under standard incubation or high CO(2) conditions (up to 4%) from embryonic day (ED) 10 onwards. The embryonic development and the hatching process of these two lines were compared when incubated under standard or high CO(2) conditions from over the second half of incubation. 3. The A line, selected for high post-hatch growth rate, exhibited a higher relative embryo weight from ED10 until ED16, which was supported by a higher air cell pCO(2), lower air cell pO(2), higher corticosterone and thyroid hormones and earlier hatching time. 4. Incubation under high CO(2) increased air cell pCO(2), retarded yolk consumption, and decreased glycogen concentration in the liver at hatch. Hatchability decreased in both lines when incubated under high CO(2), due to an increased late mortality of embryos that died before IP. 5. These results suggest that the development and metabolism of CO(2)-incubated embryos differ from control incubated embryos.

Changes in acid-base balance and related physiological responses as a result of external hypercapnia during the second half of incubation in the chicken embryo.

This study investigated the effect of high CO2 (4%) from embryonic day (ED)10 until ED16 on the acid-base balance and related parameters in the chicken embryo. From ED10 to ED16, blood was taken from a vein from the chorioallantois membrane and was analyzed for pH, partial pressure of CO2, partial pressure of O2 (pO2), [HCO3(-)], [K+], and [Ca2+]. Allantoic fluid was taken for measurement of pH, NH3-N, phosphate, and calcium concentration. The right tibia was ashed, and calcium was measured with atomic absorption spectroscopy. Embryos exposed to high CO2 showed a consistent higher blood pH than control embryos. Notwithstanding this alkalosis, bicarbonate concentration was significantly higher in the CO2 group from ED12 until ED16. Potassium concentration in the blood was significantly higher in the CO2 group from ED11 until ED16. The pH of the allantois was significantly higher on ED14 and ED15. Ammonia N concentration was significantly higher in the CO2-incubated embryos on ED12 and ED13, whereas phosphate did not differ between groups. Calcium per tibia dry weight did not differ between incubation conditions. We can conclude that embryos adapt to high CO2 during the second half of incubation by increasing blood HCO3(-). It appears that this increase in HCO3(-)is mainly the result of the stimulated intracellular exchange of H+ with K+, although temporary reabsorption of HCO3(-)by the kidney cannot be excluded.

The effect of nonventilation during early incubation on the embryonic development of chicks of two commercial broiler strains differing in ascites susceptibility.

Despite thorough selection during the last decade, the incidence of ascites is still high in modern broiler strains. Although ascites occurs mostly at the end of the rearing period, there are indications that the etiology of this problem may have started during embryonic development. Recent studies have shown that the post-hatch performance of the broiler chick might be influenced by changing the environmental conditions in the incubator during embryonic development. This study investigated the effect of increasing incubator CO(2) concentration up to 0.7%, by nonventilation during the first 10 d of incubation, on the embryonic development of 2 commercial broiler strains (Cobb and SAS) differing in their susceptibility for ascites syndrome. The Cobb strain is suspected to be less susceptible than the SAS strain. Overall, the chick embryos of the Cobb strain had a faster development than those of the SAS strain as expressed by their higher BW from embryonic day (ED)10 until ED18. Nonventilation stimulated embryonic development resulting in higher embryonic BW, early hatch, and narrower spread of hatch in both strains. In the SAS strain, nonventilation improved hatchability by more than 10%. Gas composition of the air cell in the egg of the nonventilation groups (both Cobb and SAS) had higher partial pressure of CO(2) and lower partial pressure of O(2) from ED11 until ED14 compared with the ventilation groups. During the entire incubation period, partial pressure of CO(2) was higher in eggs of the Cobb strain compared with the SAS strain. Plasma triiodothyronine, thyroxine, and corticosterone levels were different at the end of the incubation period and during hatching due to nonventilation at the beginning of incubation. It is concluded that nonventilation during the first 10 d of incubation had a stimulatory effect on embryonic development of the 2 broiler strains with no effect of heart weights but with effects on hormone levels, air cell pressures, and hatching parameters.

Critical assessment of chick quality measurements as an indicator of posthatch performance.

For hatcheries, not only is it important to have a high level of hatchability, but the quality of the chicks provided also has to be good, because broiler farmers are looking for chicks with a high growth potential, resulting in a greater slaughter yield at the end of the rearing period. However, chick quality has proven to be a difficult and subjective matter to define. Therefore, the aim of this study was to investigate the predictive value of different chick quality measurements for BW at slaughter age. Body weight, chick length, shank length, and toe length measurements as well as Tona score determination were performed on 1-d-old chicks and were linked to posthatch performance parameters. Different breeder lines (Cobb and Ross) and breeder ages (39, 42, and 53 wk of age) were used to investigate line and age effects. In addition, variability between people and repeatability in time of these quality measurements were determined. Body weight at 7 d of age appeared to be the best predictor of BW at slaughter age among all the quality measurements performed. Body weight at 1 d of age had the second greatest predictive value, closely followed by the ratio between BW at 1 d of age and chick length squared. Chick length and shank length both had low to no predictive value whatsoever for posthatch performance. The lack of significant correlations between the Tona score and posthatch performance could be explained by the absence of day-old chicks with anomalies (and thus a suboptimal Tona score) because a distinction had already been made, as is done in practice, between top-grade and lower grade chicks.

Comparison of a modern broiler and layer strain during embryonic development and the hatching process.

1. This research focused on the embryonic development of broiler and layer embryos. 2. Egg, embryo and yolk weights were measured and partial pressure of gases in the air cell and blood were analysed at several embryonic ages. The static stiffness of the eggshell was measured before the start of incubation and at embryonic day (ED) 18 to register the change in shell strength. Times of internal pipping (IP), external pipping (EP) and hatch were recorded. Plasma corticosterone, triiodothyronine and thyroxine concentrations were determined. 3. Relative egg weight loss was higher in layer eggs. Before ED16, layer embryos showed a slower development which was reflected in lower (relative) embryo weight, lower air cell and blood pCO(2) and higher air cell O(2). From ED16 onwards, relative growth rate accelerated in the layer strain; as a consequence the difference in relative yolk-free chick weight at hatch had disappeared between strains. 4. Differences in physiological events necessary for hatching (thyroid hormones, corticosterone, air cell pCO(2)) are most probably responsible for the observed differences in timing of pipping and hatching events between layer and broilers.

Acid-base balance in chicken embryos (Gallus domesticus) incubated under high CO2 concentrations during the first 10 days of incubation.

Recent studies show the importance of differential CO2 levels during the first half of incubation of chicken eggs on embryonic and postnatal growth. However, it is not known how external higher CO2 levels affect embryonic acid-base balance. In this study, the effect of an early rise in CO2, between 25th and 96th hour of incubation to 1.5% and maintained at that level until 240 h of incubation, was investigated on air cell gases, blood gas parameters from ED10 onwards and on embryonic growth and hatching parameters. Higher external CO2 concentrations resulted in a faster acidification of albumen resulting in a faster decrease of albumen pH with development, illustrating the capacity of albumen to cope with higher environmental CO2. Moreover, PCO2 in blood was higher in CO2 incubated embryos at embryonic day 10 and 11 but without a change in blood pH. The additional increase in plasma HCO3- concentration at day 10 and 11 was responsible for buffering the higher PCO2 in CO2 incubated embryos in order to stabilize pH. However, effects of hypercapnia on blood acid-base parameters extinguished 2 days after termination of high CO2 incubation. Embryonic growth was modestly accelerated which was reflected in higher embryonic weights at day 6 and 10 and a significant earlier hatching; hatchling weights were not different between treatment groups.

Effect of four percent carbon dioxide during the second half of incubation on embryonic development, hatching parameters, and posthatch growth.

In this study, broiler embryos were exposed during the second half of incubation [embryonic day (ED) 10 until ED18] to 4% CO(2). The CO(2) was set to reach 2% on ED11 and 4% from ED12 onward. Two experiments were conducted with the same setup. Embryo weight was measured and partial pressure of CO(2) and O(2) in the air cell was analyzed at several embryonic ages. Times of internal pipping, external pipping, and hatching were recorded. Chicks were raised until d 7 posthatch. Plasma corticosterone, triiodothyronine, and thyroxine concentrations were determined. Embryonic growth was not retarded and hatchability did not decrease in the CO(2)-incubated group, demonstrating that chicken embryos can tolerate high (4%) concentrations of CO(2) between ED10 and ED18. In the first experiment, partial pressure of CO(2) in the air cell was significantly higher in the CO(2) group on ED11, ED12, ED13, and ED14, but disappeared thereafter. This difference was not observed in the second experiment. A change in the hatching process of the CO(2) group was seen. Relative growths of newly hatched chicks until d 7 posthatch were equal in the CO(2) group and the control group. However, corticosterone and thyroxine concentrations were significantly higher in the CO(2)-incubated chicks on d 7 posthatch.