The effects of acid and aluminum on growth and growth related endocrine function in domestic and wild birds

Declines in wild bird populations are due in part to environmental contaminants, including direct and indirect consequences of acid precipitation (decreasing pH, increasing dissolved aluminum). Direct effects of acid precipitation would include ingestion and absorption of acid and/or aluminum and the toxicity involved. Indirect effects include a decrease in the availability of food due to toxic effects of acidified environments on all levels of the food chain. The effects of aluminum and acid on growth and growth related endocrine function were examined in chickens, mallard ducks and black ducks. Growth-related endocrine function was evaluated as plasma levels of growth hormone (GH), insulin-like growth factor-1 (IGF-1), and insulin-like growth factor binding protein (IGFBP) levels. Chickens and mallard ducks were fed diets containing aluminum sulfate, or sulfuric acid. Pair feeding of birds with the control diet to the aluminum and the acid treatments was included. Black ducks were maintained on man-made ponds that were either acidified, acidified with the addition of aluminum, or circumneutral. Nutritional status caused changes in body weights and organ weights in these studies. Plasma levels of GH tended to be increased while plasma levels of IGF-1 were decreased in birds exposed to the toxicants and birds experiencing reduced feed intake (chicken study, black duck studies). A 22kDa IGFBP was increased in pairfed birds in the chicken study. Higher molecular weight IGFBPs were increased in birds in the treatment groups in both the chicken and the black duck studies. Results from these studies identify that different species of birds have different sensitivities to acid and aluminum in the diet and to the effects of restricted feed intake. It is concluded that aluminum and acid exert toxic effects on avian growth both directly and indirectly.