It takes you directly into the heart of the rendering facility; and what has been kept hidden from the consumer. Leftover meat scraps and any unused animal parts began to be added to pet foods around the time of World War II. Back then, very few people understood the nutritional requirements of cats or dogs, and so the idea stuck for many years; and continues to do so to this day. While recent years have brought many advances in animal nutrition and veterinary research, we still have a long way to go before most pet foods contain the kinds of protein that our companions need.
Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.