Some people believe that if a dog is used as a stud dog his temperament will change and he might become more aggressive or his temperament may change somehow. However, this is not normally the case at all.
What will happen is that your stud dog will become more aware of bitches. When he is with a bitch in season, his natural stud dog instinct will take over. Like most dogs around a bitch in season, he is likely to become less interested in his owner or other things such as toys or food, and instead be more focused on the female dog. The scent of the bitch will not alter his temperament, although if other male dogs are around he may be less sociable with them.
You will find that with experience, the stud dog will not bother bitches that are coming into or have just come out of season and will only be mildly interested until she is ready for mating, which is usually only a period of 4-5 days during the three weeks or so that she is in season.