MATERNALLY DERIVED PROGESTOGENS INCREASE EMBRYONIC GROWTH RATES EARLY IN DEVELOPMENT IN THE CHICKEN (GALLUS GALLUS)
Maternal steroid levels in chicken eggs impact embryonic development. Conditions experienced during embryonic development have the potential to produce lifelong effects. The general trend, from humans to birds, is for offspring that are larger at the time of birth to have increased survival. And in birds the best predictor of hatch mass is egg mass, where larger eggs produce larger offspring. However, we unexpectedly found that early in embryonic development (7 days of incubation), chicken embryos developing in small eggs were actually larger than those in large eggs. This led to the question: Are there yolk steroids that are more abundant in smaller eggs that could increase embryonic growth rates? To begin to answer this question, 60 eggs were collected at the time of laying for the quantification of yolk steroids prior to development. After data analysis, three progestogen steroids (progesterone, pregnenolone, pregnanedione) were found to be more abundant in smaller eggs. Based on this, we further hypothesized that supplemental injections of these progestogens would produce larger embryos after seven days of incubation. To test the hypothesis, a second experiment consisted of 60 eggs, split into two groups. The experimental group received a cocktail with steroid ratios based on the average levels found in the first 60 egg yolks (12µg progesterone, 120µg pregnenolone, and 280 µg pregnanedione in 100 µL oil). The control group received an equivalent volume of pure oil. Both groups were incubated at 37º C and 65% humidity for seven days. At the end of the seventh day, it was discovered that the progestogen-injected eggs produced significantly larger embryos. These embryos were then molecularly sexed and embryonic sex did not influence embryonic mass. These findings suggest that smaller eggs contain increased levels of maternal progestogen steroids such as progesterone, pregnenolone, and pregnanedione and supported the hypothesis that these increased levels aid in developing larger embryos after one week. Future studies will investigate how maternal progestogens influence embryonic growth later in development.
Damery, Konnor, "MATERNALLY DERIVED PROGESTOGENS INCREASE EMBRYONIC GROWTH RATES EARLY IN DEVELOPMENT IN THE CHICKEN (GALLUS GALLUS)" (2019). University Research Symposium. 259.