Hormonal treatments can be used to control reproduction in dogs, cats and ferrets. These are not generally recommended by vets because neutering brings many health benefits and the medications can cause serious side effects. However, in certain situations birth control by medication can be effective and practical.

One common option is an implant containing deslorelin. This is administered under the skin by a veterinary surgeon to male dogs and ferrets to cause temporary infertility. In the dog, it can take 8-12 weeks to bring about infertility, the testicles are seen to reduce in size and the dog becomes less interested in bitches in season. The infertility usually lasts 12 months, testicle size may increase around this time or a blood test can be taken to measure testosterone to see if the implant is no longer working. Implantation can be repeated when the first or subsequent implants run out. Dogs cannot be treated until they reach puberty, and there is limited information about dogs under 10 kg or over 40 kg. This is essentially temporary chemical castration.

Castration of any kind, surgical or chemical, should be considered very carefully in aggressive dogs, whether they are aggressive to people or other dogs as certain types of aggressive behaviour can actually be worsened by the drop in testosterone levels.

The implant causes infertility in male ferrets for up to 4 years. A short general anaesthetic is usually used to apply the implant so that the ferret is still and the implant can be placed securely.

In the female dog, cat or ferret, hormonal medications can be used to prevent or postpone their seasons. Bitches cycle every 6-12 months throughout the year and queens every 21 days in the breeding season, ferrets also cycle constantly through the breeding season. If their seasons are postponed or prevented, females of the three species will not be sexually active or fertile. There are 2 licensed synthetic progesterones that postpone seasons if used once, and prevent them if used repeatedly, working in a similar manner to the human mini pill. One is injectable (proligestone), the other tablets given orally (megestrol). Both are prescription only as there are important considerations about their use and severe potential side effects. Neither can be used in animals in their first season. They must be administered at the first signs of the pet coming into season and the animal may still be fertile for the first few days. The injectable form can be repeated to stop further seasons. The oral version should not be used on 2 consecutive occasions and is not recommended in breeding animals. Seasons can be erratic after treatment with either but in theory fertility is not affected by either treatment in the long term. Both medications should be avoided in animals with diabetes mellitus. If a pet has had treatment for a false pregnancy at the previous season, it is not safe to use either medication.

The most serious potential side effect of the medications is inflammation or infection of the uterus or womb. In 0.3% of bitches treated with the injectable medication, uterine infection is reported. Unfortunately, uterine infection or pyometra is a life threatening condition and emergency surgery plus antibiotics and fluid therapy is usually required to treat it. The infection can damage the kidneys and liver making the anaesthetic more complicated, and the presence of pus in the uterus carries a risk of septicaemia. The injection can be painful when injected, while the tablet form can have steroid side effects, causing the dog or cat to drink more and urinate more; there is also a danger of illness if the medication is withdrawn quickly. Weight gain and lethargy are common after this treatment and it can predispose to cancer of the mammary glands and diabetes.

There is current research into another means of birth control. This involves giving the animal anti hormone antibodies to stop their hormones working. None of these are consistently successful yet but research continues.

If an unwanted pregnancy does occur in a bitch or queen there is a licensed veterinary medication which causes abortion, aglepristone. This can be used up to 45 days of pregnancy in bitches and 35 days in queens. In dogs about 1 in 20 puppies will continue to be carried after the injections, so the bitch should be checked 10 days after injection and a month after mating to ensure the pregnancy has ended. The next season may occur very early after this drug is used. Again, it cannot be used in bitches with diabetes mellitus and injection can be painful.

There are advantages to surgical neutering, above and beyond birth control. It is normal for bitches to have false pregnancies after a season. Often the bitch becomes withdrawn and may protect toys or objects that she treats like her puppies. She may also produce milk. False pregnancies can be distressing for the dog and owner. Neutering removes ovaries so that the bitch no longer cycles, so false pregnancies no longer occur. Uterine infection or pyometra cannot happen in neutered bitches as the uterus is removed. Mammary cancer is also much more common in unneutered pets and as our pets live longer this is a common life limiting condition. Neutering males also prevents testicular cancer, which is common in older dogs. Unneutered male cats tend to have a much shorter life because of injuries sustained from fighting and roaming further to finds queens. Feline Immunodeficiency Virus (FIV) is sexually transmitted and, in some areas of the country, there is a high risk of an entire tomcat catching this life limiting viral infection.

Laparosopic spaying (keyhole surgery) is now common in the UK as well as the standard surgical method, this is a less invasive method of neutering. Unfortunately, there are still a large number of pets in rescue and anything we can do to reduce unwanted pets in the UK is helpful.

Do you want to know more? Give your vets about birth control in your pets!