My Great Dane Valentina always did tire out quickly after the amputation. After she was healed she initially seemed more active for longer but I think it was because she was tired of laying around for so long and she was ready to get up and go. Then after a while she seemed to get tired quicker. She would be so excited to go outside and wanted to run at first but it wasn't long before she was tired and needed to rest. She would have her initial burst of energy and then I knew when she was tired because she would go stand by the door asking to go back inside. Then she would immediately go lay on her bed. Over time I did notice her seeming to slow down a little at a time. She stopped wanting to chase her toy at all most days. Some days she would want to but the days started to get fewer that she wanted to. She always wanted water as soon as she came in from outside and when she came in and went to her bed without getting water first I thought it was odd. And then some days she didn't even really want to get up to go out or it would take her longer than before to get up. Not really realizing until now that all of that was signs that something was making her more tired and possibly painful. I just thought she was having some days when she just didn't feel like doing certain things just like I do sometimes. Then one day she started having alot of trouble walking and then only a couple of days later she could not walk at all. The vet determined that she had severe spinal arthritis and her spinal nerves were being compressed. We tried confinement and high dose steroids but they didn't work so we had to put her to sleep on Feb 3rd. It's weird now because I totally remember seeing all of those little changes then but didn't realize what was going on until it got really bad. I wish Dogs could talk.It would be so much easier. I tried manipulating Valentina's legs also to see if she was having pain anywhere back there but noticed nothing. I think that she was getting tired so quick because her legs were not cooperating with her so much anymore. I still remember watching her walk around and noticing that she seemed a bit wayward. (She had her left front leg amputated) The vet said that with all of the extra weight on only one front leg it put extra stress on her spine causing the arthritis. I especially noticed her having problems squatting to pee. Valentina lived for 7 months after her surgery and I am thankful for every day that we had the pleasure of spending with her. I really hope that your Mastiff doesn't have anything serious going on. What's his name by the way? Hope you can figure out what is going on and that the shots and exercises will help. Praying that he feels better real soon and that you have much much more time together. Hope I am not freaking you out with my story but I think it is good to know different things that it could be when you notice something different with your Dog. I had no idea that it was something with her spine. At first I thought one of her legs was hurting but that was not the case at all. I do also think that it is still early in you Dog's recovery so it could just be that he needs to build up his strength and endurance. You will be in my thought s and prayers.

Angel and Valentina Angel Dane