Early spaying in cats and dogs, especially before reaching sexual maturity and their first heat cycle, has been a common practice for decades despite the fact that evidence suggesting there are significant adverse impacts that have been known for quite some years too.
The main argument for the neutering of both sexes is fundamentally one of convenience for owners not to have to cope with females in season, pining males, and to remove owner responsibility to ensure there are no unwanted pregnancies. Veterinarians have pushed early neutering not only on this basis, but by stating the myth that was dispelled many years ago that spaying before 6 months old reduces the chances of mammary tumours later in life. If I remember correctly, my small animal surgery professor who lectured us on spaying told us it wasn’t true some 30 odd years ago, but I still hear of it being quoted now. It is a lie. It has been the case in some European countries for quite a few years now that neutering is considered “an unnecessary mutilation unless for medical reasons”. They didn’t come to that conclusion without good reason.
It goes without saying of course that if body parts such as ovaries, uterus and testes are removed they cannot become cancerous later in life, and pyometras are mostly avoided too, although stump infections are still possible albeit very rarely. Pyometra is when the uterus becomes infected and fills with pus. If the cervix is open then there will be evidence leaking out, but if closed then it is often diagnosed based on females being off colour with/without reduced appetite, increased temperature, drinking more water than usual, excessive licking of the vulva, distended abdomen and in more advanced cases vomiting and collapse. Early detection enables it to be potentially treated medically, but if surgery is required then it is better the less infection there is which reduces the risk of the uterus bursting during the procedure as it becomes increasingly friable. Higher levels of infection will also increase the body’s toxicity and impact on other organs such as liver and heart which will also need to cope with a general anaesthetic and recovery.
I keep coming back to the diet of course because inappropriate ingredients as found in kibbles and other processed pet foods will increase systemic inflammation and thus the risk of cancers and infections too. The inclusion of plant materials with their anti-nutrients that include carcinogens and hormone disruptors cannot do anything other than increase these risks too.
It should be no surprise either that removal of the gonads and the alteration to hormones that causes will have health implications elsewhere. No body system functions in isolation to the rest of the body and yet there is a tendency amongst all medical professionals to pigeonhole body systems, and even elements within a system, without consideration or appreciation for how that impacts the rest of the body. To put it more simply, the more reductionist is the approach the more we focus on the minutiae at the increasing expense of the big picture. Consequently, there is growing concern about the potential adverse health implications of early spaying, particularly related to the loss of hormones. This is true for both males and females.
Luteinising Hormone (LH)
The primary hormone that mediates the adverse effects is Luteinising Hormone, usually abbreviated to LH. Removing the gonads eliminates the normal negative feedback provided to the anterior pituitary gland that produces and releases LH. As a result, persistent LH concentrations in neutered individuals can be over 30 times higher than those left intact.
When LH binds to its receptors, it causes nitric oxide secretion and cell proliferation. Following gonad removal, LH binds in much higher numbers to receptors in the bladder, skin, thyroid, adrenal cortex, ligaments, subchondral bone, blood vessels, lymphocytes, and behaviour centres of the brain to cause a wide range of health problems for the remainder of the individual's life.
Persistently high LH therefore increases nitric oxide production which increases the production of prostaglandin 2 that causes inflammation. Nitric oxide also increases the expression of the EGR1 gene which performs important functions in tumour cell proliferation, angiogenesis, metastasis, invasion, and immune responses in hypoxic situations, but can suppress cancer in others by increasing apoptosis and supporting DNA repair. Nitric oxide also upregulates epiregulin which increases cell proliferation and inflammation.
Orthopaedic Issues
Some studies suggest that early neutering of both sexes may be linked to an increased risk of orthopaedic issues such as hip dysplasia and cranial cruciate ligament tears due to ligament laxity. The hormones produced by the ovaries and testes play a role in the development of bone and joint health, and their removal through neutering at a young age may disrupt this development. In males this manifests as delay in the closure of the growth plates which means they grow bigger than they otherwise might have done. We also know from the German studies over 30 years ago that commercial kibbles etc are highly implicated in all developmental orthopaedic problems. Combined with early neutering and obesity from unnecessary carbohydrates in the diet it is no surprise how many dogs end up having cruciate ligament problems resulting in very expensive and often radical surgery. All factors are converging against them, and all are avoidable.
Urinary Tract Issues
Hormones also influence the development of the urinary tract system. Early spaying has been associated with an increased risk of urinary incontinence in female dogs. This condition can lead to urinary tract infections and other related health issues, not to mention the stale urine smell that will inevitably require considerably more frequent cleaning of dogs bedding and potentially restricts where you can allow them to go in your home. Increased bodyweight will also make this worse.
Behavioural Changes
Hormones play a significant role in behaviour, including aggression, fearfulness, and anxiety. Early spaying or neutering may alter the behavioural development of cats and dogs, potentially leading to behavioural issues such as increased aggression or fearfulness.
Weight Gain
A variety of hormones control and regulate metabolism and energy balance mostly through the pituitary and hypothalamus feedback loops. To certain degree all hormones are this interlinked. Some studies have suggested that neutering at an early age may predispose cats and dogs to weight gain and obesity later in life but how much is from neutering and how much might be diet-related or the combination, is probably unclear.
Cancer Risk
As I’ve already pointed out, the absence of certain organs prevents those cancers, but there is significant evidence that high LH from early neutering increases the risk of other types of cancers. This includes osteosarcoma (bone cancer) and haemangiosarcoma (a type of blood vessel cancer).
Neutered bitches were found to have 4 times as many haemangiosarcomas than entire bitches. Mast cell tumours are not seen in entire dogs, and lymphomas are 3-5 times more frequent in neutered dogs. The earlier the gonads are removed, the sooner the onset of the cancer.
Other options
To reduce the risk of these health problems, veterinarians should provide dog owners with surgical and non-surgical sterilization options that do not involve removing the gonads.
Gonad-sparing neutering
Gonad-sparing neutering, sometimes referred to as partial neutering or sterilization, aims to preserve the presence and more importantly, the function of the gonads (ovaries or testes) while still preventing reproduction. This approach allows individuals to retain some or all of their reproductive hormones, which is clearly preferable to the adverse consequences of traditional neutering. There are a number of options for gonad-sparing neutering as follows…
Ovariectomy or Vasectomy
Instead of surgically removing the entire reproductive organs (ovaries or testes), a partial removal procedure can be performed instead. In females, an ovariectomy removes the ovaries whilst leaving the uterus intact. This is the normal procedure in France which prevents pregnancy while preserving hormonal function. Although the uterus remains it does not appear to increase the incidence of pyometra. In males, as happens with human, vasectomy involves the surgical severing or blocking of the vas deferens, which prevents the release of sperm only whilst maintaining the production of testosterone.
Tubal Ligation or Hysterectomy in Females
In the same way that a vasectomy physically stops sperm from being able to be released, tubal ligation involves the surgical blocking or tying off of the fallopian tubes, thereby preventing eggs from physically reaching the uterus ready to be fertilized. This preserves ovarian function and hormone production while preventing pregnancy. Similarly, a hysterectomy involves the surgical removal of the uterus while leaving the ovaries intact, providing permanent contraception whilst maintaining hormonal balance.
Hormonal Contraceptives
Chemical neutering, also known as chemical castration in males, involves the use of drugs to suppress the production or function of reproductive hormones. Different countries likely have different options, so discuss which are available where you are with your regular veterinarian. These medications work by altering hormone levels to prevent ovulation in females or sperm production in males. However, long-term use of hormonal contraceptives have potential side effects and are not always recommended as a solution, especially if you are thinking of breeding a bit later in life. Permanent hormonal interference will of course impact other body systems and metabolism in similar ways to full surgical neutering. There are a few options for chemical neutering, each with its potential downsides:
Deslorelin implants: Deslorelin is a GnRH agonist, which means it initially stimulates the release of reproductive hormones, but with continuous administration, it suppresses them. Deslorelin implants are inserted under the skin and gradually release the hormone. The possible downsides include one or more of the following…
Temporary increase in hormone levels before suppression.
Side effects such as swelling, itching, or hair loss at the implant site.
Variable efficacy and duration of action, with some dogs experiencing a return to fertility after the effects wear off. You therefore cannot stop being vigilant if you use this method with females especially.
Gonadotropin-releasing hormone (GnRH) vaccines: These were what the WHO added to the human tetanus vaccines for girls in Kenya without discussion or permission. GnRH vaccines work by stimulating the immune system to produce antibodies against its own GnRH, thereby reducing hormone levels such that they cannot maintain a pregnancy. Downsides may include…
Variable efficacy (as with all vaccines) which means not all individuals will produce enough antibodies to sufficiently lower GnRH to stop a pregnancy being maintained.
Delayed onset of action, requiring several weeks to months to achieve full effect.
Possible adverse reactions as happens with the more commonly administered “routine” vaccinations: namely injection site reactions or allergic responses.
Anti-androgen drugs: These drugs block the action of androgens (male hormones) and are sometimes used for chemical neutering, particularly in cases where reducing testosterone levels is the primary goal. The downsides may include…
Inconsistent efficacy, with some individuals not responding adequately to treatment.
Potential side effects such as decreased libido, weight gain, or feminization in males.
Long-term safety concerns, as these drugs will have effects on other body systems besides the reproductive system.
Oestrogen-progestogen combinations: These drugs are sometimes used to suppress reproductive hormone production in females. They aim to work by mimicking the hormonal changes that occur during pregnancy, thereby suppressing seasons and temporary infertility. Downsides may include…
Possible serious side effects such as uterine infections (pyometra) or mammary gland tumours.
Risk of unintended pregnancy if the timing of administration is not precise.
Consequently they are not suitable for long-term use due to associated health risks.
Summary
Reproductive cycles are a normal part of life and perform functions beyond just fertility. In my opinion, animals have their rights to express themselves in this way. As owners we have a duty to do the best we can for our animals whilst at the same time preventing unwanted pregnancies. Wherever possible, that includes ensuring taking the proper and necessary precautions during those relatively short times when females are fertile, albeit that this comes with varying degrees of inconvenience. There will be certain situations where such inconveniences require intervention, but there are options that don’t require permanent surgical mutilation and which will significantly reduce the adverse impacts of full surgical neutering as listed above.
I have recently bought two puppies, a male and female from different litters but too closely related to breed. My vet tells me that dog vascectomies are not available in the UK and for bitches, the only alternative to full spaying is removal of the ovaries. Surely there must be a vet who is willing to do this as I am not prepared to follow the conventional advice and am so pleased that your research highlights these matters.
Great article, thanks. So important not to spay young (or at all if you can) especially when those cancers like osteosarcoma, are harder to treat & with a poor prognosis.
Our Springer Spaniel is now 5 and still intact. He was unfortunate to get a mast cell tumour at 6 months old - incidentally it first appeared at 3 months, straight after puppy jabs. Thankfully it hadn’t spread and he’s happy and well.