Validation of an egg-injection method for embryotoxicity studies in a small, model songbird, the zebra finch (Taeniopygia guttata)

Female birds deposit or ‘excrete’ lipophilic contaminants to their eggs during egg formation. Concentrations of xenobiotics in bird eggs can therefore accurately indicate levels of contamination in the environment and sampling of bird eggs is commonly used as a bio-monitoring tool. It is widely assumed that maternally transferred contaminants cause adverse effects on embryos but there has been relatively little experimental work confirming direct developmental effects (cf. behaviorally-mediated effects). We validated the use of egg injection for studies of in ovo exposure to xenobiotics for a small songbird model species, the zebra finch (Taeniopygia guttata), where egg weight averages only 1 g. We investigated a) the effect of puncturing eggs with or without vehicle (DMSO) injection on egg fate (embryo development), chick hatching success and subsequent growth to 90 days (sexual maturity), and b) effects of two vehicle solutions (DMSO and safflower oil) on embryo and chick growth. PBDE-99 and -47 were measured in in ovo PBDE-treated eggs, chicks and adults to investigate relationships between putative injection amounts and the time course of metabolism (debromination) of PBDE-99 during early development. We successfully injected a small volume (5 μL) of vehicle into eggs, at incubation day 0, with no effects on egg or embryo fate and with hatchability similar to that for non-manipulated eggs in our captive-breeding colony (43% vs. 48%). We did find some evidence for an inhibitory effect of DMSO vehicle on post-hatching chick growth, in male chicks only. This method can be used to treat eggs in a dose-dependent, and ecologically-relevant, manner with PBDE-99, based on chemical analysis of eggs, hatchling and adults.

► We validated an egg-injection method to study in ovo exposure to xenobiotics. ► Zebra finch eggs (1 g) were injected with 5 μL DMSO, safflower oil, or sham-injected. ► Neither embryo fate nor hatchability was affected by vehicle or egg-injection. ► DMSO had an inhibitory effect on post-hatching growth but only in male chicks. ► Egg-injection is a suitable method for embryotoxicity studies in small passerines.