DDT thins shells of eggs from mallard ducks maintained on ad libitum or controlled-feeding regimens.

Mallard ducks were fed diets containing various levels of technical DDT or chemically pure p,p'-DDT, or dieldrin. Either technical DDT or p,p'-DDT at 20 ppm or greater, or dieldrin at I 0 ppm caused a statistically significant reduction in e9gshell thickness, weight, and calcium. Shells of eggs from ducks fed 40 ppm of p,p -DDT were about 20% thinner than those from control ducks, and shells of eggs from ducks fed I 0 ppm of dieldrin were about 6% thinner than those from controls. The reduction in eggshell thickness was linear with increasing dose of DDT to 40 ppm, and with increasing dose of dieldrin through ail levels studies. Eggshell thinning occurred regardless of whether the diets containing DDT were fed under ad libitum or controlled conditions. DDT fed at 200 ppm was lethal to the ducks. Neither DDT nor dieldrin affected weight of the eggs or rate of egg production.