- Small dogs (less than 20 pounds): Every 18-24 months or every 2 heat cycles
- Medium dogs (20-50 pounds): Every 12-18 months or every 2 heat cycles
- Large dogs (over 50 pounds): Every 9-12 months or every 1-2 heat cycles
Cats
- Intact female cats (queens): Every 4-6 months if they are allowed outdoors and have access to other cats, although some queens may come into heat more often
- Neutered female cats (queens): Do not come into heat