A 2 lb difference in the dogs could easily be a genetic difference. In any litter of pups you can find a wide variance.

The hormones approved for beef cattle, and sheep production consists of: estradiol, progesterone, testosterone, zeranol, trenbolone acetate, and melengestrol acetate.

One could further group them together as:

estrogen, zeranol - female hormones, although zeranol is also anabolic
progesterone, melengestrol acetate - progesterones
testosterone, trenbolone acetate - anabolic male hormones

Most of the cattle implants are either a combination of estrogen plus progesterone, or a balance of estrogen plus trenbolone. There's a withdrawal period before slaughter that brings the levels down to within normal levels in the animal. Heating or cooking would destroy additional residue in the meat, and the natural hormones are additionally broken down by stomach acid. But let's assume a pharmalogical amount makes it through the meat supply to humans (or dogs). In the case of teenagers eating heavily contaminated meat with female hormones, at best you'd end up with a population of sterile males, and females having trouble ovulating. Don't believe we've reached that point yet. Also the presence high levels of female hormones forces the closure of the growth plates resulting in shorter height. But what about the male hormones listed above? Most are used in the small number of female cattle being raised for market. Most female cattle are retained for breeding, or maybe more accurately as incubators for embryos.

The documentary you saw was either made in the 50s or is totally inaccurate. It's illegal to use any hormones in chickens. The last tried was the infamous DES used in the 50s, and banned in the early 60s. Turkeys have been genetically bred and altered by us to be extremely top heavy, and can barely walk much less fly like their wild cousins. The same genetic program has been applied to chickens. The controversy for chickens and a valid one is the usage of Antibiotics . Not because of the left over residue in the meat, but because of the real possibility of Antibiotic resistance occuring in the bacteria, making the Antibiotic useless to treat life threatening infections in humans. It does no good to invent the next generation of Antibiotics and see resistance rapidly arise to them.

In summary the amount of hormones in beef and sheep meat in commercial dog food is below detectable levels. By definition there are no elevated hormones in the chicken used in commercial dog food. Therefore hormones are not being pumped into commercial dog food.