Environmental toxicity studies using chickens as surrogates for wildlife: effects of vehicle volume.

Domestic chicken embryos are frequently used for avian developmental toxicity studies of polyhalogenated aromatic hydrocarbons, which are often injected into eggs with oil-based vehicles. The volume of toxicant and vehicle injected ranges from relatively low volumes (0.1-0.5 microl/g egg) to relatively high volumes (1.0 microl/g egg and above). Previous research from our laboratory suggested that high volumes of vehicle oil may disrupt normal growth of chicken embryos, possibly from hypoxia-like effects. This analysis explored the potential effects of vehicle volume on developing chicken embryos. We assessed standard measures of mortality, organ growth, body growth, and behavior from chickens developmentally exposed in ovo prior to incubation to low (0.1 microl/g egg) or high volumes (1.0 microl/g egg) of corn oil injected into airsacs or to no injection. The chickens receiving high volumes of oil showed increases in overall embryonic mortality and early embryo mortality compared to chickens receiving low volumes of oil or no injection. The chickens receiving high volumes of oil showed decreased activity during righting reflex, running time, visual discrimination, and olfactory aversion tests, and increased activity during an open-field activity test compared to chickens receiving low volumes of oil or no injection. Somatic endpoints do not appear to be affected by high volume injections. These results suggest that high volumes of vehicle injected into airsacs of eggs may lead to hypoxia-like conditions that increase embryonic mortality and disrupt simple behaviors. However, some effects of volume may diminish when injections are performed later in incubation.