SynovexC at spring working on steers. SynovexS at fall weaning/working. For the cost, 1lb. of gain pays for the implant. I like the Synoved gun best. Last Ralgro gun I saw didnt have the retractable needle like Synovex. I never implant heifers so I have the option to retain replacements. Always afraid I'd make heifers grow well enough I'd want to keep them for growth, or someone buys them to breed and has huge issues, ruins my reputation for quality stock. My vet warns against implanting heifers. Says they tend to bag up, bull alot, and messes up heat cycles.