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Differential incubator CO2 levels at different developmental stages of
chicken embryo to improve post-hatch performance
 

 

   Kokou Tona

 

Incubating egg characteristics are related to the strains or lines and age of breeders, and the egg storage conditions. However, all incubating eggs are incubated under standard conditions. This research program aims to investigate how incubator CO2 levels depending on the egg storage duration and the line of breeders can improve hatchability and chick quality.

Research problem statement

Intensive and focused selection over many years have significantly improved growth rate of broiler breeders and their progeny in order to achieve increased meat yield. As a result, broiler breeders consume more feed and grow faster (Nicholson, 1998 and Havenstein et al., 1994). This induces high metabolic demands, which leads to a number of metabolic problems such as disturbances in energy metabolism and therefore overall performance. Indeed, ascites and sudden death syndrome are the most prevalent cardiovascular diseases among modern broiler flocks (Olkowski and Classen, 1998; Korte et al., 1999) with negative impacts on animal welfare. According to Decuypere and Verstegen (1999) almost 50% of normally accepted mortality among broiler chicks is due to ascites.

From our previous studies, it was discovered that long storage of eggs resulted in slower developmental rate of the embryo and therefore in longer incubation duration,  lower T3 levels in 18-20 days old embryos and lower pCO2 in egg air chamber indicating lower metabolic rate (Tona et al., 2003). These effects of storage on egg quality and embryo development resulted not only in a depressed effect on hatchability but also in a decreased chick quality and chick growth (Lapao et al., 1999; Mather and Laughlin, 1976 and Tona et al., 2003). The comparative similarity in the physiological parameters of embryos from ascites sensitive lines vs ascites resistant lines (Dewil et al., 1996) with those of embryos from long-stored vs short-stored eggs is striking and indicates that eggs stored for longer duration before incubation may be more susceptible to ascites incidence in later life.

 

Hypothesis and objective

It is well known that changes in some physiological parameters such as heart rate or corticosterone concentration are an indication for stress level. In the chick embryo, corticosterone can be detected in blood around 10th day of incubation (Wise and Fry, 1973; Kalliecharan and Hall, 1976 and Iqbal et al., 1989) although pituitary control of adrenal function becomes only important at about day 14 of incubation (Wise and Fry, 1973). Freeman and Flack (1980) reported a negative correlation between basal concentrations of corticosterone and the relative increase in circulating corticosterone after handling stress. Moreover,  Darras et al. (1996) and De Groef (2003) reported an increase in circulating T3 and T4 in chicken embryo subjected to dexamethasone (DEX), corticotropin-releasing hormone or adrenocorticotropic hormone injection. According to Decuypere et al. (1990), glucocorticoids and thyroid hormones are involved in the preparation for hatching. Also, Decuypere et al. (1983) and Meeuwis et al. (1989) demonstrated that corticosterone was required for the peripheral conversion of T4 to T3 during prenatal life. Since stress factors are involved in the induction of hatching, it can be hypothesised that advancing hatching time by artificially inducing stress factors such as corticosterone may have beneficial effects on ascites sensitive lines during embryonic life and possibly reduce the incidence of ascites development. On the other hand, because early hatching leads to better post-hatch growth (Tona et al. 2003), stress factors that can advance hatching time may also improve post-hatch growth. The aim of this PDM program follow up is to study the responsiveness to corticosterone and thyroid hormones of 15 or 18 days-old embryos from ascites sensitive or ascites resistant lines injected with DEX, a long-term acting glucocorticoid that mimics high corticosterone levels. Also, the effects of DEX injection on hatching parameters, chick quality and post-hatch growth will be investigated.

This work is closely linked with ongoing projects in which collaborating members in our laboratory are working with the non-invasive tools that are and have to be further developed for embryo studies in order to facilitate embryo research depending on breed genotype lines. Also, other members of our laboratory are investigating the effects of incubator CO2 level on embryo chorio-allantoic membrane development and molecular changes in developing embryos.

 

Methodology 

Two different experiments with several incubation settings each will be studied in order to investigate the effects of DEX injection in embryos and its interatction with genotype lines on embryo physiology, hatching and production parameters.

 

1.        In experiment 1, incubating eggs will be collected from dam line broiler breeders that are resistant (dAR) or sensitive (dAS) to ascites and set at day of collection or stored for 7 or 14 days before setting. The effects of ascites prevalence x egg storage duration on embryo physiological parameters (T3, T4 and corticosterone levels) and early production parameters (hatchability, chick quality and broiler juvenile growth) will be studied. Also, the responsiveness of embryos from eggs of ascites sensitive and ascites resistant lines to corticosterone, T3 and T4 levels upon DEX injection will be studied. This study can provide an idea as to how long these eggs should be stored in order to minimise the ascites problems but also will provide information about whether it is a failure of stress control during embryonic life that is associated with later ascites.

  

2.        For the second experiment, incubating eggs will be  collected from a broiler breeder commercial line. The effects of DEX injection on hatching time and post-hatch growth will be investigated. This study will bring out the difference or the similarity between the effects of chemical stress factors and environmental factors such as incubator CO2 levels (see first year program) which is investigating for the same goal, advancing hatching time.