Some bodybuilders and athletes use trenbolone esters for their muscle-building and otherwise performance-enhancing effects.  Such use is illegal in the United States and many other countries. The DEA classifies trenbolone and its esters as Schedule III controlled substances under the Controlled Substances Act .  Trenbolone is classified as a Schedule 4 drug in Canada  and a class C drug with no penalty for personal use or possession in the United Kingdom .  Use or possession of steroids without a prescription is a crime in Australia .  The infamous "duchess" cocktail administered to Russian athletes at the Sochi Winter Olympics consisted of oxandrolone , a metenolone ester, and a trenbolone ester. 
About the only time they are given en masse in the feedlots is as an abortifacient (abortion-causing drug). They are used here in combination with a prostaglandin to ensure very close to a 100 per cent abortion rate. It is for this reason that when used for other purposes, a veterinarian must warn of the possibility of aborting in pregnant animals. Calving is initiated from cortisol coming from the fetal adrenal gland, so using the steroids to initiate calving mimics this process. Sometimes steroids and prostaglandins are given to every heifer in the feedlot, and sometimes veterinarians will palpate the heifers and only use the products on the pregnant ones. Either way one shot of this combination relieves many calving-related problems later on in underage heifers.