Weight Gain

• Neutered cats and dogs are both more likely to become overweight after surgery, partially because testosterone is necessary for maintaining a fast metabolism.
  
  

Arthritis

• Because additional weight can stress a pet's joints and ligaments, it is not uncommon for neutered animals to develop arthritis or ligament degeneration later in life.
  
  

Lethargy

• After neutering, some pets become lethargic because of metabolic slow-down. Fortunately for high-strung and anxious pets, this change in personality can sometimes be a blessing.
  
  

Respiratory Problems

• A male animal's chest may narrow after neutering, especially if he is neutered before puberty. This may cause respiratory disorders.
  
  

Anesthesia Complications

• Complications from anesthesia are rare, but they do sometimes occur. An animal may aspirate vomit if he has eaten recently, or may experience cardiac arrest if he has an undiagnosed heart defect.