And little comment from me....we have over 60 rabbits and we don't have a smell. But if I do....I am looking for a problem such as intestinal parasites (hookworms can cause a terrible odor), coccidia (which has a very unique smell) or a urinary problem (such as infection, EC marker or dehydration). An improper diet....too much protein (pellets and junk treats)...can overload the cecum and cause the poop to be smelly and the additional protein canstress the kidneys resulting in a urinary smell. Bottom line,if I have an unusual odor, I'm looking for the root cause.
And since your rabbit is male and about 4 months old....and if he has not been neutered....you have a teenager in full hormones. We affectionately call this smell"Boy Bunny" as their male hormones are raging and they want everyone to know. If you don't pay attention...you will get a urine shot most likely in the face....my wife loves that. Neutering will resolve this behavior. The earlier a male is neutered, the less time it takes for the hormones to purge from the body. Not only do you have a more docile rabbit and there will be no possibility of an undesired pregnancy should he meet an unaltered girl.....it will alsoeliminate thepossibility of testicular cancer. We have a testicular cancer survivor in our sanctuary.
Randy