I'm not an expert on chicken doping, but aren't most eating chickens male and wouldn't you more likely pump them up with chicken steroids to bulk them up? Chicken breasts aren't mammary glands, so estrogen wouldn't have any special effect on them.
"Modern commercial broilers, for example, Cornish crosses or Cornish-Rocks, are specially bred for large scale, efficient meat production and although they are the same species, grow much faster than egg laying hens or traditional dual purpose breeds. They are noted for having very fast growth rates, a high feed conversion ratio, and low levels of activity. Broilers often reach a slaughter weight of four to five pounds (dressed) in only five weeks, (another source indicates six to seven weeks as typical) although more slow growing free-range and organic strains reach slaughter weight at 12 to 16 weeks of age. As a consequence, their behaviour and physiology are those of immature birds rather than adults. Typical broilers have white feathers and yellowish skin. Recent genetic analysis has revealed that at least the gene for yellow skin was incorporated into domestic birds through hybridization with the Grey Junglefowl (G. sonneratii). Modern crosses are also favorable for meat production because they lack the typical "hair" which many breeds have that necessitates singeing after plucking.
Both male and female broilers are reared for their meat."