In male rabbits, testosterone production and its accompanying effects typically start to become noticeable around the age of 3-4 months. This is when they reach sexual maturity and begin exhibiting behaviors associated with breeding and dominance. The exact timing can vary slightly depending on the individual rabbit and breed, but it generally occurs around this age range.

Once testosterone kicks in, male rabbits may start displaying behaviors such as spraying urine to mark territory, mounting other rabbits or objects, and becoming more aggressive or territorial. It's important to be aware of these changes and provide appropriate socialization, environmental enrichment, and, if necessary, separate housing for intact males to prevent fighting or unwanted breeding.

If you plan to keep a male rabbit intact for breeding purposes, it's essential to provide proper management and ensure he has appropriate housing, companionship, and breeding opportunities if desired. If you do not intend to breed your rabbit or wish to avoid certain behaviors associated with intact males, neutering can be considered. Neutering is a surgical procedure to remove the testes and is commonly performed on pet rabbits to prevent reproductive-related issues and modify behavior. Consulting with a veterinarian experienced in rabbit care is recommended to discuss the best options for your specific situation.