WHAT ARE THE SIGNS THAT YOUR DOG IS GOING INTO HEAT

There's something special about female dogs. They're fiercely loyal, they can be unbelievably sweet, and they definitely have their very own personalities. When you have a female dog, though, there's one extra bit of care with which you need to be familiar. If your dog isn't spayed, then being able to recognize the signs of a dog in heat can help you to keep her safe and healthy.
The good news is that dogs don't go into heat too frequently, so you don't need to worry about female dog in heat behavior all that often. If you don't plan on breeding your dog, then spaying her can put an end to unwanted dog in heat symptoms.
 
Your female dog will experience her first heat cycle when she reaches sexual maturity, which is around six months of age. Dogs come into heat about twice per year, though small breed dogs may experience three heat cycles per year. Giant breed dogs may only have one heat cycle every 12 to 18 months. Young dogs may initially experience irregular cycles. Your dog's heat cycle will last for about two to three weeks on average. The exact duration of her heat cycle can vary, too, so it's best to know how to identify signs of a dog in heat to better monitor your dog.
 
It is important to understand the symptoms when your dog is in heat. With such knowledge, you will be able to manage her reproductive cycle.
 
Phase One – Proestrus
Phase one happens in the first week. Proestrus is the term to describe the initial stage of the heat cycle. It can happen from 7 days to 10 days. Some dogs even experience the phase more than 10 days. The very first thing to notice as a symptom is the swelling of your dog’s vulva. But it does not always happen in the first day. You May notice it after few days of phase one.
You may also see few symptoms as mentioned below:
Behavior Changes: The changes can be mild to severe. That will depend on your dog’s heat.
Appetites: The significant appetite changes are often showing that the Dog is in heat. Your dog might skip her lunch a bit. In some cases, the dogs have no appetite at all.
Bleeding in the Vulva: The bleeding can vary between one dog to other.
Swelling of the Vulva: Check your dog vulva whether it is swelling or not.
Tail Tucking: Your dog might guard the vulva by tucking her tail. She usually positions her tail between the legs. If other dog approaches, there’s a chance that she will be sitting to cover up her vulva.
Phase Two – Estrus
This usually happens in around the second week of the heat cycle.
 the estrogen level of your dog will decrease significantly. When this happens, the ovaries begin to send off the eggs for fertilization. You can read these symptoms to confirm:
Softer Vulva: The swelling causes the vulva to soften. This is enough for penetration.
Tail Flirting: Usually, the dog will turn her rear toward the male dog and position her tail upside, opening the access to her vulva.
Phase 3 – Diestrus
It is the end of the heat cycle. You could see the symptoms below:
Vulva Swelling Disappearance: It does not happen overnight, though. In most cases, the swelling will be gone in a week.
Decreasing Lust: Your female dog will show lack of interests to mate. She will tend to reject the male dogs’ flirts.