Dog Sterilization Options: What You’ve Never Been Told Before

Both male and female domestic dogs reach sexual maturity (also known as puberty) between the ages of 6 and 12 months. This is true for both sexes.

In the case of certain large breeds, this procedure can be put off for as long as two years.

It is possible for your dog to become pregnant as early as the first oestrus cycle; however, it is not recommended to breed your dog before the second cycle in order to help your dog reach sexual maturity.

As is the case with other domesticated species, the process of domestication has resulted in dogs having a stronger libido, as well as earlier and more frequent breeding cycles, than their wild ancestors had.

In domesticated species one of the first and strongest effects seen from selective breeding is selection for cooperation with the breeding process as directed by humans.

One of the behaviours noted is the abolition of the pair bond seen in wild canines.

The ability of the female domestic dog to come into estrus at any time of the year and usually twice a year is also valued.

The amount of time between cycles varies greatly among individual dogs, but a particular dog’s cycle tends to be consistent through her life.

Conversely, wild species generally experience estrus once a year, typically in late winter.

Most dogs come into season for the first time between 6 and 12 months, although some larger breeds delay until as late as 2 years.

Like most mammals, the age that a female first comes into season has multifocal contributions of genetic, hormonal, dietary and nutritional, and behavioural signals to both physical and sexual maturation.

The relationship between body fat and body mass correlates well with the onset of puberty in most mammals.

They then experience estrus about every seven months until old age.

Female dogs do not experience menopause like elder female humans, although their cycles will become irregular and fertility becomes unpredictable as they become older.

Dogs over around 7 or 8 years are not usually considered appropriate for breeding, but can still remain fertile.

Male dogs are receptive to mating at any time, even if the female is not in estrus.

Gestation in a dog is 63 days in length, if measured from the day of ovulation. Since it is difficult to determine the exact date of ovulation, errors are often made in calculating gestation period.

 Canine sperm can live for 10 to 11 days in the uterine tubes (fallopian tubes) so if a bitch is bred 10 days before the eggs can be fertilized, she will appear to have a gestation length of 70 days. If she is bred on the day the eggs can be fertilized, her gestation length will appear to be 60 days long.

An average litter consists of about six puppies, though this number may vary widely based on the breed of dog. Toy dogs generally produce from one to four puppies in each litter, while much larger breeds may average as many as 14 pups in each litter. 

The number of puppies also varies with the mother’s age and health, the father’s sperm count, the timing of the breeding, and many other factors.

Common Methods Of Reproductive Control

Birth control methodadvantagesdisadvantages
neutering– decrease urine marking
– decrease the smell of urine
– decrease mounting other animals
– decrease roaming
– decrease fighting with other male animals
– permanent birth control
– prostate cancer is prevented
– Infertility is irreversible
– Possible weight gain
– risks associated with anaesthesia
– possible surgical complications
– possible bleeding, scrotal swelling
– possible Infection
spaying– Permanent birth control
– The dog will be friendlier
– Fewer behavioral problems
– Zero risk of breast and reproductive system cancers
– No bloody oestrus cycles
– Infertility is irreversible
– Possible weight gain
– Possible incontinence
– Possible wound opening
– Accidental ligation of the urethra
Birth control pills– Effective Birth control
– Infertility is not permanent
– Frequent infections of the uterus
– Skin problems
Management of access– Method does not interfere with nature
– A pregnancy can always follow if chosen
– Very difficult to control
– Strict confinement have to be applied
Termination of pregnancy– No unwanted litters– Not ethical
– Not safe for the mother

Surgical Sterilization

Surgical sterilization is the most common method used for permanent reproduction control in dogs and cats. The most widely available, convenient and reliable option for reproduction control, surgery is a one-time procedure that lasts the life of the animal without any further caretaker effort.

The most widely performed procedures are “spays” (usually referring to an ovariohysterectomy where the ovaries and uterus are removed in females) and “neuters” (where both testicles are tied and removed from males). These procedures have advantages and disadvantages that should be weighed by owners.


Neutering with removal of the testicles has several advantages in addition to reproductive control. Since the testicles produce the male hormones that control male-specific behaviours, neutering tends to decrease behaviours such as:

  • urine marking,
  • mounting other animals,
  • roaming
  • fighting with other male animals
  • By removing the testicles, cancer of the testicles, the second most common tumour in the male unneutered dog, is prevented. Cryptorchid dogs (those that have testicles that never descended into the scrotum so are not visible externally) have a very high risk of cancer if not neutered.
  • Other testicular diseases such as infection, as well as diseases of the secondary sex organs like the prostate (which will occur in many unneutered males as they age) are prevented.
  • Neutering also removes the more pungent odour of the intact male’s urine.

It will not change basic personality patterns such as watch-dog barking, hunting activity, playfulness, activity level and seeking affection. One study showed that male intact cats exhibited less affection to humans than neutered cats.

Rare complications include risks associated with anaesthesia and surgical complications, bleeding, scrotal swelling and infection. A common misconception is that after neutering, males will become lethargic and gain weight. No published evidence shows a change in appetite or exercise after neutering.

Some possible explanations for the misconception may be the decreased roaming activity and decreased fighting between males. Any weight gain can be controlled by the caretaker decreasing the animal’s available food intake.

It should also be noted that sperm may still be found in the male for up to 21 days in the dog and up to 49 days in the cat after neutering and may cause pregnancy if allowed to breed.

An alternative to surgical neutering with removal of the testicles is a vasectomy where the connection between the testicles and the body is tied off, leaving the testicles in the scrotum. This procedure is not widely performed because it does not provide the medical benefits such as decreased cancer risk nor does it affect male-specific behaviours such as intermale aggression while carrying similar risks to neutering.


Dog spaying (bitch spaying procedure) – otherwise known as female neutering, dog sterilization, “fixing”, desexing, ovary and uterine ablation, uterus removal, or by the medical term: ovariohysterectomy – is the surgical removal of a female dog’s ovaries and uterus.

The main purpose for spaying is:

  • canine population control
  • medical health benefit
  • genetic-disease control
  • Behavioural modification.

Considered to be a basic component of responsible female dog ownership, the spaying of female dogs is a simple and common surgical procedure that is performed by veterinary clinics all over the world.

Mammary cancer is the most common tumor of the intact female.

If female dogs are spayed prior to their first estrus, risk of this cancer is only 0.5%.

But after 1 cycle the risk increases to 8% and after 2 cycles to 26% with not much effect if spayed later than that.

So, in order to gain a major medical benefit, the procedure must ideally be done before the first heat cycle.

No benefits have been shown by allowing a female to experience her first cycle before spaying.

Spaying also prevents pyometra (infection of the uterus which can be very serious and even fatal), decreases urine marking, prevents cycling behaviours and bloody discharge associate with heat, and avoids disorders associated with pregnancy and birthing.

Although rare, anesthetic and surgical risks (<0.1%) have been reported, including wound opening, infections, bleeding, incomplete removal of ovaries and uterus, and accidental ligation of a ureter. A more common complication is incontinence in dogs (<1%) as they age due to a weakened bladder sphincter which is estrogen sensitive.

This problem can be treated pharmaceutically. If food intake is regulated, no weight gain is seen postoperatively. A decrease in activity by some females after spaying has been attributed by some to changes in activity with increasing age, especially since spaying has traditionally been done at about 6 months of age when activity levels often start to decline normally.

As with neutering, there are other surgical options that do not remove all the uterus or ovaries, but these procedures are not widely performed due to a lack of health benefits and one is still subjecting the animals to the same surgical risks.

Non-Surgical Alternatives

The widespread success of contraceptive used by women and their high degree of efficacy has sparked a great interest in applying these techniques to controlling reproduction in pets.

One of the problems with this method is that dogs are not women, and tend to be significantly more sensitive to negative side effects of steroidal contraceptives.

Steroidal Contraceptives

Several steroidal contraceptives similar to those used in women have been evaluated in dogs and, to a lesser extent also in cats. Many of these treatments are quite effective in preventing conception. The problem is that they also carry a high risk of inducing serious uterine disease in bitches that are on these contraceptives, most prominently pyometra (pus-filled uterus).

This is an infection of the womb and uterus and can cause severe illness and even death.  If caught in time the only way to rectify this is by total removal of the womb.

In the United States, two steroidal contraceptives are currently available for dogs. Neither drug is approved for use in cats.

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Megestrol Acetate

In the United States, the progesterone hormone, megestrol acetate, is marketed to suppress estrus (“heat”) in dogs. This means that the dog will skip her cycle and not go into heat. It has been reported to be safe and effective for this purpose when administered during the appropriate period of the cycle of the female.

To suppress estrus, it has to be given orally for 8 days, then this have to be done about every 4-6 months. Some of the negative side effects reported, includes weight gain, increased appetite, drinking and urinating more, diabetes, depression, lethargy, changes in temperament, infections in the uterus, suppressive effects on immune status, adrenocortical suppression and hair loss.

It is not frequently used in the U.S. due to the repeated treatments required and the severe side effects possible. It is not currently approved for use in cats in the United States.


Mibolerone is an androgen hormone that is approved for estrus prevention in dogs. It is only approved for up to 2 years although it has been shown to work for up to 5 years of continuous treatment.

It is given at least 30 days prior to the expected estrus and is given daily as a liquid added to food. It has caused vaginal discharge and clitoral enlargement in some dogs as well as some possible liver toxicity with various doses. It is not currently approved for use in cats in the United States.

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Strict Management Of Access To Other Animals

Another method of preventing unwanted litters is to prevent access of your animal to other breeding animals.

Both males and females that are capable of reproducing should be restricted in their access to other animals. Dogs and cats do escape from houses and backyards, or other animals may be able to enter these areas where your animal is kept.

If this is the chosen method of reproductive control, a very diligent owner is needed to closely supervise the animal and have safeguards to prevent other animals from approaching and mating as well.


It is possible for dogs to be spayed whilst they are pregnant, however, it is not as safe nor as ethical as performing the procedure on a non-pregnant animal. The procedure is, after all, performing an abortion on a creature that cannot choose for itself and many veterinary staff and clients do have concerns about the ethics of this.

From a procedural and safety viewpoint, the uterus of a pregnant dog is very large and thickened compared to a non-pregnant uterus, with extremely large ovarian and uterine blood vessels supplying it.

A much longer incision needs to be made into the dog’s abdomen in order to remove a pregnant uterus safely (trying to pull a large, pregnant uterus out through an undersized abdominal incision can result in the uterus tearing and falling apart and contaminating the abdominal cavity with fetal and placental fluids).

Because there is a much greater chance of a pregnant uterus hemorrhaging as it is being removed, extra care has to be taken in legating the ovarian and uterine blood vessels. In addition to this, the surgery takes longer to perform (longer anesthetic time) and it costs more to the client.

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