How does growth hormones effect our cows?

Cows these days have growth homone injected into them and they can be seen in the cows' meat and their milk. The cows are injected with rBGH or recombinant bovine growth hormone. This hormone was found to be in two thirds of the cows slaughtered last year. This hormone leads to higher milk production and more beef in the cows but is it healthy for human consumption.
rBGH is a genetically engineered hormone that is injected into the cows. It is produced under the commercial name of Posalic and was approved by the FDA in 1993 despite some controversy. Skeptics of the hormone claim that there was no proper testing of the hormone and that the FDA relied solely on the tests that Monsanto, the production company, ran on lab rats. Before approval, there was no long term test for the hormone on cows. There are reports that the hormone may kill cows from mastitis which is an infection of the utter. The hormone actually decreases the cows' original production if they stop injecting it.
The hormone increases the IGF-1 or insulin growth factor-1 levels in the cow which is linked to prostate, breast and colon cancer in humans. This increases the cancer rate in the cows with in turn would lower the level of the beef and dairy. There is no test to prove that the IGF-1 leads to high cancer risk with consumption through the meat or dairy of a rBGH cow.
Chemistry is needed to understand this to understand the reaction that takes place. Without our knowledge that reactions lead to other reactions we would not fully comprehend that the rBGH leads to the release of the IGF-1 which causes cancer.

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"The Issues: RBGH." Sustainable Table. 29 Jan. 2008 .