I need some advice guys. This morning Payton picked a fight with Auggie. This is actually the third time this week. The first was Monday night, I was sitting on the couch watching the basketball game while all the dogs were playing on the floor. I don't know what happened, but suddenly Payton was snarling and going at Auggie and Auggie was trying to get away making yelping sounds. Pulled Payton off and it stopped immediately. Auggie was fine, it was just a lot of noise. Payton ran up to Auggie about five minutes later and was licking all over his muzzle, then invited him to play, they played and chased each other and it was like it never happened. Last night everybody came in from going potty and because it was pouring rain I had towels to dry them off. I dried off Pepper first, then told Payton "get in your towel" (which he knows from going to the lake) and was drying him off. Auggie wandered past and Payton started growling at him, seriously. I told Auggie to get away and Auggie was moving away and Payton lunged at him - I caught Payton since I was toweling him off, told Auggie to get away again, and finished toweling Payton off with no problems, then was able to dry Auggie off with no problems. Payton was kind of walking around looking at Auggie a bit sideways but I told him to lay down and he settled down and that was the end of it. This morning they came in, it's still raining. I put a towel over Pepper, put a towel over Payton, and was reaching to put a towel over Auggie when Payton started growling at him. I reached down to grab Payton and he lunged at Auggie snarling and fighting. Auggie again was just trying to get away making yelping sounds. I pulled Payton off and he was snarling and growling and kept trying to get at Auggie. I took him to the opposite side of the room and kept drying him off and the whole time he was snarling. I tried putting the towel over his head so he couldn't see Auggie but that made it worse. After I was done drying him off I took him and Pepper in the other room, crated Pepper, then crated Payton... just quietly, I didn't really say anything, just put him in there. He was expecting me to fill up his twist n treat like I normally do but I didn't think it was a good idea to give him a bucket of cookies after attacking Auggie, so I didn't... so he had some loud crate tantrums while I finished getting ready. I left the room, toweled off Auggie, and put Auggie away too so Auggie wouldn't come in the bedroom while I was still getting ready and wander by the crate and antagonize Payton more. I think Payton was trying to pick a fight with Auggie at some point on Saturday too, or maybe Friday night, because I distinctly remember after they all got baths and I was brushing out Payton telling him "I'm sorry I threatened to chop your balls off," so he must have tried to pick a fight with Auggie over something and I told him if he didn't quit I was going to chop his balls off. But I don't remember what happened and it was not a full-on fight. The towel thing seems simple enough, it seems like resource guarding. Is he guarding me or the towel, or the experience of being toweled off by me? And why is he only going after Auggie? Pepper was standing right next to Payton while all this went on this morning and he didn't even look at her. It specifically seems to be Auggie. He has never tried to pick a fight with Pepper, or with Georgie. Auggie has no testicles but ultimately he IS a boy... Payton will be two years old in May. I'm assuming first thing to do is take him to the vet and have them take a look at him. He had a T4 run at his 1 year annual and it came up totally normal, I would be a little surprised if it came up unusual now. Also he has had the recent change in his food. Is this ridiculous or can a change in food bring this on? He's eating a LOT more now, he gets 2/3rds per meal twice a day (and still isn't putting on a ton of weight either, but at least he's not pooping in the house or having any kind of diarrhea.) It's lower protein and lower fat, so I would kind of expect the opposite honestly. I didn't sleep well last night because of all the rain and flooding going on here so I'm really overly tired, and I'm really emotional right now, but if it were up to me I would be calling the vet and making an appointment to have him neutered. I know it's a kneejerk reaction and not really logical right now but I am seriously considering it so it's not off the table. I've brought it up with the co-owner and asked her input as well, if this is just some kind of "I'm almost two so I'm testing how much of a jerkface I can be" type of thing or if we need to be considering something more serious here. Since he was bought with the potential to be used in her breeding program we have to discuss it anyway. ETA: the only other thing I can think of is Auggie has been on Baytril for his UTI for the last two weeks, he just got his final pill this morning. Maybe he smells differently because of the abx?