How to Prevent Your Dog From Going Into Heat

Updated: 9/30/2021

Female dogs go into heat, or experience an estrus cycle, when they reach reproductive maturity. This point can occur anywhere from 6 months of age, though 8 to 9 months is more common. A dog’s first heat may be as late as 18 months of age, which is more common in large breeds.

Dogs come into heat about twice a year, and heat cycle lasts about 3 weeks. When a female dog is in heat, she is receptive to mating and can become pregnant; female dogs will not accept males for breeding when they are not in heat.

Pet parents of a dog in heat may notice the following symptoms:

• Swelling of the vulva
• Bloody discharge
• Lethargy
• Agitation
• Aggression

Dealing with a dog in heat can be stressful. Can you prevent dogs from going into heat? Is it possible to delay your dog's heat cycle? We'll explore the answers to these questions, but first, let's take a look at how a dog's heat cycle works.

The heat cycle is a naturally occurring part of your dog's reproductive cycle when her body prepares for pregnancy. Let's explore what happens during the 4 phases of a female dog's reproductive cycle:

• Beginning of heat, or proestrus (3 to 17 days): The body produces estrogen and bloody vaginal discharge to prepare for mating.
  

• Full heat, or estrus (4 to 7 days): The body releases luteinizing hormone. Bleeding may continue, but usually decreases. Ovulation occurs; dog is receptive to mating.
  

• End of heat, or diestrus (6 days): Discharge ceases. If the dog doesn't become pregnant, the body reabsorbs the uterine lining.
  

• Non-heat or anestrus (2 to 3 months): The dog isn't hormonally active or sexually receptive.

If you're not planning on breeding your dog during a heat cycle, not only can unwanted symptoms such as vaginal discharge and behavioral changes prove difficult to manage, but the chance of your dog becoming pregnant from an unplanned breeding is a very real possibility.

If you're not planning to breed your dog, the best way to prevent her from going into heat is to spay her. Two spay procedures are performed on dogs: ovariohysterectomy (OVH) and ovariectomy (OVE).

What's the difference between the two? An ovariohysterectomy involves the removal of the uterus and both ovaries. With an ovariectomy, only the ovaries are removed, with the uterus left intact.

North American veterinary surgeons once preferred OVH, but OVE is becoming more common. Experts once believed that OVH better protected dogs from reproductive diseases, like pyometra and cancer. Leaving the uterus intact increases the possibility of uterine tumors.

However, a 2014 study found that uterine tumors in spayed animals are rare, and up to 90% of them are benign. This is because hormones from the ovaries often cause uterine diseases; without the ovaries, animals have a much smaller chance of developing serious disease.

OVE is also less invasive, resulting in fewer complications, less anesthesia, smaller incisions, and faster recovery times. Your vet will advise you on which procedure is best for your dog.

Can dogs get spayed while in heat? Yes, but vets generally advise against it. Because blood flow to the reproductive organs increases when your dog is in heat, the risk of hemorrhage increases. You may want to wait until a few months after the heat cycle has ended.

If your dog isn't able to be spayed due to a medical condition or you'd like to breed her at a later date, megestrol acetate can delay or prevent heat cycles. Other medications that prevent and permanently suppress heat cycles include mibolerone and proligestone, but these aren't available in the US.

Megestrol acetate is available in pill and liquid form. Before starting this medication, your dog will need to undergo:

• a heat cycle history
• physical exam
• breast cancer check
• vaginal smear

One study found that megestrol acetate had a 92% success rate in delaying the heat cycles of dogs in the early proestrus phase and a 98% success rate in dogs in the anestrus phase.

Dogs who haven't yet experienced their first heat cycle shouldn't take megestrol acetate. Female dogs shouldn't be bred within 30 days of completing their megestrol acetate regimen. Do not use this medication for more than 2 heat cycles.

Side effects are common and may include:

• weight gain
• behavior changes
• breast tumors
• adrenal gland suppression
• increased thirst
• uterine infections

Due to the potential for serious side effects, dogs taking this medication need careful monitoring. Your vet will check your dog's weight, blood sugar levels, liver function, and reproductive health. Tests can also determine how well the medication is working.

Heat cycles in dogs who aren't breeding are inconvenient and stressful for pets and pet parents. Besides the chance of an unwanted pregnancy, they are messy and can result in behavioral changes in your pet that most pet parents aren't prepared to deal with.

The best way to prevent dogs from going into heat is by getting them spayed. Not only will this prevent unwanted pregnancies, but it also prevents several serious reproductive diseases, such as pyometra and cancer.

Reproductive conditions in intact female dogs can be expensive to treat. If you plan to keep your female dog intact, start searching for pet insurance today. Brought to you by Pet Insurer, Wag! Wellness lets pet parents compare insurance plans from leading companies like PetPlan and Trupanion. Find the “pawfect” plan for your pet in just a few clicks!