- Normal variation: The age of first heat can vary widely among dogs, even within the same breed. Some Yorkies may not go into heat until they are 12 or even 18 months old.
- Health problems: Certain health problems, such as hypothyroidism or Cushing's disease, can delay the onset of heat. If you are concerned about your Yorkie's health, take her to the vet for a checkup.
- Nutrition: A diet that is deficient in certain nutrients, such as protein or zinc, can also delay the onset of heat. Make sure your Yorkie is eating a high-quality diet that is appropriate for her age and activity level.
- Stress: Stress can also delay the onset of heat. If your Yorkie is experiencing a lot of stress, such as from a move or a change in routine, try to minimize the stress as much as possible.
If your Yorkie is still not in heat by the time she is 18 months old, you should take her to the vet to rule out any underlying health problems.