Neutering in Dogs Volume 60- Issue 3

Francisco Javier Fernandez Martin*

• ACV, Cynological Judicial Expert and Canine Nutritionist, Spain

Received: February 06, 2024; Published: February 17, 2025

*Corresponding author: Francisco Javier Fernandez Martin, ACV, Cynological Judicial Expert and Canine Nutritionist, Spain

DOI: 10.26717/BJSTR.2025.60.009470

Abstract PDF

Castration is a controversial method, used in different countries for various purposes. The most striking are the alleged or theoretical fight against animal abandonment defended by the different animal protection associations, as well as preventing reproduction. In the same way, it seems that an argument in favor is that it prevents certain diseases, however, all these campaigns on castration must be studied, as there are many studies that shed light on the pathologies that are created, aggravated or developed by direct or indirect fault of castration. Likewise, there are alternative methods to the usual and expensive form of surgical castration. In this article we will try to show the myth about animal abandonment and the non-neutering of dogs, as well as the relationship that exists between some of the most common diseases that can be caused by neutering a canid, without a real medical reason.

Abbreviations: EF: Economic Factors; CI: Unwanted Litters; FTC: End of Hunting Season; CP: Behavioral Problems; PIA: Loss of Interest in the Animal; CD: Change of Address

The most common way to sterilize animals is surgical. However, there are other ways, not so common and little used in veterinarians, such as chemical castration or, better called, chemical sterilization. The most common way is to use different drugs, such as chlorhexidine digluconate in dimethyl sulfoxide, gossypol, deslorelin, zinc gluconate (sclerotization method), which resulted in the loss of sperm-producing tissue, without affecting testosterone and the dog’s health, as well as being a viable alternative to surgical castration, Calcium chloride (another method of sclerotization) may also be used to reduce longterm sexual behavior, although testosterone level also decreased. In addition to these products, chlorhexidine gluconate, zinc arginine, formalin, ethanol injection, silver nitrate, acetic acid, sodium tetradecyl sulfate, sodium moruate, potassium permanganate (in the vas deferens) has been used (Navarrete Gahona, et al. [1-7]).

Another method used is the use of calcium chloride in saline solution, with different concentrations (between 10 and 60%), it seems an appropriate method if the concern is obesity, since the dogs studied did not change their weight, although there were some adverse reactions, such as testicular inflammation and testicular fistulas, caused by the puncture in the testicles and not by reactions to the solution (Leoci, et al. [8]). A new technique, allowed in the European Union since 2008, consists of performing implants that release GnRH (gonadotropin). They are composed of desloreline or azagly-nafarelin.

The advantage of this system is that it is placed subcutaneously, between the shoulder blades, with a syringe and the other similar one (azagly-nafarelin), is used in the same way, but near the navel, initially used for females. That is, the shape is similar to that of a vaccine. The product called Gonazon was the one used, until the authorization was withdrawn at the request of the marketing owner in 2012. This product was effective until 7 years of age and its composition was 18.5 mg. The interesting thing about this drug is that several studies were carried out and, in some of them, adverse effects were shown, such as anxiety, weight gain and benign prostatic hyperplasia (Driancourt, et al. [9-13]).

Another medication used in dogs and cats is known as covinan, its active ingredient is proligestona. It is not used in Europe, but it is used in South America. This substance, as with all progestogens, has been linked to cases of diabetes (due to insulin resistance), overproduction of growth hormone and suppression of the hypothalamic- pituitary-adrenocortical axis. It is used as an injectable, subcutaneously to prevent heat and psychological pregnancies. It can also be contraindicated, as it can cause pyometra in the dog if injected during the proestrus season (vaginal bleeding). Similarly, progestogens are known to induce ectopic production of growth hormone in the mammary gland, which can lead to a high incidence of breast tumors. In cats it seems that problems similar to those of the dog occur (Salud Animal, et al. [14-16]). Deslorelin, mentioned at the beginning of this chapter, seems to be one of the most widely used drugs because it is one of the drugs with the fewest adverse effects, as long as the conditions of injection and use are met. It seems that this type of medication is used, above all, in males, both dogs and cats. It is not so common to use it in females, as it seems that there are adverse effects, such as urinary incontinence, recurrent induced heat, uterine diseases, ovarian tumors, body weight gain, behavior change, induced heat, changes in coat, psychological pregnancy, ovarian cysts, etc., These effects seem common in both dogs and cats (Sp, et al. [17])

Every year new drugs come out to avoid surgical interventions on animals or, rather, to be able to sterilize animals in a reversible way. As with all medicine, studies and a lot of money are required to carry out professional research and obtain the appropriate certifications for its use and trade. In the same way, it seems that another intermediate treatment (between chemical castration and complete surgical castration) is not used either, this would be tubal ligation (salpingectomy -removing or ligation-) in the case of females, either in cats or in, and vasectomy in males, both cats and dogs, since it would be the system that would really prevent reproduction and would not prevent the formation of hormones for proper development of each animal. The advantage that vasectomy would have over orchiectomy lies in the fact that the male would continue to maintain testosterone levels, for example, for sports animals. This operation would lead the animal to azoospermia, achieving infertility. The problems that may appear are spermatocele, sperm granuloma and testicular degeneration, but there do not seem to be neurological or cognitive conditions. In the case of females, whether in cats or dogs, salpingectomy has the same effect as vasectomy, that is, there would be no hormonal alteration in the animal, which would imply that the adverse effects of conventional castration could be avoided (Urfer, et al. [7]). There may be some economic interest in surgical treatments, as the prices of a surgical castration can be around €400, while chemical casing can be around €50 per year (prices in Spain, year 2024/2025).

It is interesting to know how different associations and political strata focus their campaigns on promoting castration (surgical sterilization), regardless of the animal species (cats or dogs, above all) and the sex of the individual. Thus, certain campaigns promoting the sterilization of domestic dogs and cats can be seen in different municipalities, without entering into the money that animal protection associations receive for this or another purpose from the public treasury [in 2024, they received more than 1.9 million euros from the State, plus millions from the different autonomous communities]. Among the campaigns that stand out is that of the Salamanca City Council in 2022, when the slogan used was: “sterilize today and avoid abandonment tomorrow”, making clear the reason why they promote sterilization. Another was that of the Mijas town hall in 2019, where it could be read: “let’s avoid more homeless pets. Sterilizes. The cost of sterilization is lower than that of having to take care of the offspring (...)”. What follows are demonstrations on the false argumentation to, possibly, cause diseases in animals, by a fight against abandonment that in no way is achieved by castrations and, in addition, these campaigns are taking for granted that every animal with an owner, without sterilizing, ends up having offspring, as if the owner of each animal were not responsible and prevented a male from mounting a female, or, without providing facilities for the owners to find a home for the young, even if there is no economic benefit. (Ministerio de Derechos Sociales, Consumo y Agenda [18,19]).

A country that is used a lot as an example for having hardly any abandoned animals is the Netherlands. It has a population of just over 17 million people. And, fundamentally, they have more cats than dogs, but this is not for pleasure, but for economy. On the one hand, depending on the city, you can pay about 100 euros (on average) per year in taxes for having a dog, plus then the tax that these same animals have classified as “purebred”, as well as the penalties and fines that are imposed for abandoning, mistreating, abusing animals, etc., reaching 3 years and more than 16,000 euros, respectively. Cats are tax-free and, in addition, they have certain premises with advantages where feline colonies exist, such as the “cat boat”, although a second boat was withdrawn from them in 2006 (Dozet Kapor, et al. [20-22]). Likewise, in the telegraaf newspaper, there is a tendency to collect news of abandoned dogs, such as the German shepherd found in the Havelte forest, in 2022 (Meppelink [23]) It is interesting to know that “there are no abandoned dogs” due to the severe laws that exist, but it must also be clarified that neutering is mandatory. Another country, which is barely mentioned as an example, probably because it does not defend the same interests as in the Netherlands, is Norway. This country has an Animal Welfare Law, where it is forbidden to sterilize animals, except for medical problems. In Norway there are also “no stray or abandoned animals” and they are not obliged to sterilize them. It should be noted that no news stories about abandoned dogs have been located in newspapers since at least 2019 (aftenposten, vg, dagbladet and adresseavisen). This same law, in its article 34, dictates that a fine must be charged in proportion to the seriousness of the infraction, as well as taking into account the salary of the person who is fined. The Norwegian penal code leaves the sanction open to the economic possibilities of the accused. According to some news about animal abuse found in the Norwegian newspaper (LOVDATA [24]) (LOVDATA [25]). Aftenposten, it is possible that the penalties could reach two and a half years in prison. Other sentences have been 15 days and 6,000 crowns, around 600 euros. It is also worth mentioning the case of the United States, where more than 85% of dogs are neutered and, however, there are costs for overpopulation of dogs and cats between 1,500 and 2,500 million dollars per year [2004-2016], which results in neutering not being effective against animal abandonment. (Oberbauer AM, et al. [26-28]).

As a result of the previous study on the United States, others have been carried out in the same country, and also in Canada and Brazil. These studies concluded that neutering did not prevent animal shelters from becoming saturated, nor did animal abandonment on the street reduce. The interesting thing about the previous studies is that one of them was funded by a foundation called “Maddie’s Fund”, which strongly believes in funding spaying programs for dogs and cats, but just its final conclusion was: “no clear results were found demonstrating the impact of total spay/neuter procedures on shelter admission” (Urfer, et al. [7,29-33]). From Germany there are publications in which the “rigorous reason why there are no abandoned dogs in Germany” is because of fines of up to € 25,000 and prison sentences, however, some news related to animal abandonment has been collected in German newspapers, thus, the newspaper Bild, published in 2019 the abandonment of puppies in Hamburg, another news item published in 2022 about the release of a dog in Munich. An interesting news item from the same newspaper, from 2021, explains how Jörg Langer has gotten a new vehicle for €16,000 to be able to rescue abandoned animals and to help other people go to the vet, what need would there be to rescue animals if they do not exist? Likewise, it seems that castrating is prohibited and a fairly high fee, hundreds of euros per year, is also paid for the possession of an animal (La República, et al. [34-37]).

Likewise, it should be noted that in Spain there are no official data on abandonment, basically because no one has bothered to carry out real censuses. The only way that exists, and it is not at all exact, to be able to make an estimate of the abandonment is with the reports that the Affinity Foundation makes annually. A brief analysis can be carried out since the Foundation showed this data publicly. The interesting thing about the data itself is that, as the Foundation itself explains, they must be used with great caution (something that the Protectors and others ignore... “we believe that the study is being misused and the data is being misinterpreted”, as it seems that these statistics from the Foundation are carried out with 10% of all cases, which means that of the remaining 90%, they cannot know the origin of the animals, just as they cannot know the data on abandoned animals, those who have not arrived at a shelter or those who have been sacrificed, having said that, we will proceed to carry out the analysis on abandonment, with the scarce data available: (Fundación Affinity, et al. [19,38]) It would be very difficult to reach any conclusion with the data provided, for the simple reason that they are incomplete data and of a very low percentage to carry out a reliable study. As mentioned at the beginning, these data should be taken with caution and do not have to represent the reality of what is happening in Spain with dogs. These data are made with only 10% of all possible reasons and the main reasons do not include large percentages, but are percentages, which rarely exceed 15% of the total reasons. In addition, it is interesting to note how economic reasons represent important effects for dropout. In other words, the fact that unwanted litters in 2020 represent 21% of total abandonment, when it is subject to 10% of cases in which the reason for abandonment is known because it is the owners who take the dogs to the shelters, means that, in reality, the percentage of unwanted litters is 2.1%. In addition, it should be taken into account that this statistic is carried out with a total of 1,544 collection centres, of which 250 are municipal and 1,294 are protective. In other words, the data used to draw up laws or statistics and “convict” unneutered dogs or their owners, are data completely provided for these purposes and by the main stakeholders, far removed (or not) from reality (Table 1).

Table 1:

Note:
• The number of abandoned dogs must be taken with caution.
• According to the report itself, they represent 2% less than in 2008.
The reasons why, in 2011, 2012 and 2014 there are no studies published by this Foundation, are unknown.
In this year, modifications were made in terms of the way data of the Study were collected. Censuses of Protectoras were obtained and the results changed directly.

It can be seen that the dogs that go to shelters the most are adults/seniors (6/10 [2020 study]; 7.8/10 [2021 study]; 7.5/10 [2022 study]), when, according to studies and the justification of the shelters’ actions, unwanted litters seem to represent one of the main problems, and here the following question arises: if unwanted litters are the main reasons for abandonment, According to these studies, why are adult dogs the majority of abandoned dogs (+60%)? It is complicated, in turn, to understand that dogs that are mixed breeds represent the highest percentage of abandoned dogs (at least, according to studies [±80 % - in this order of percentage of abandoned mixedbreeds: 2023: 72%; 2022: 71.2%; 2021: S/N; 2020: 60%; 2019: 80%; 2018: 80%; 2017: 81%; 2016: 81%; 2015: 81%; 2014: 84%; 2010: 82%; 2009: 85%]), while those of race are the most stigmatized and least abandoned. It should be clarified that they know that they are a breed because the owner who abandons the animal must provide the papers that prove it, otherwise they will not be able to know if they are a breed or not because they would lack the official documentation that is necessary to ensure and guarantee that they meet the standards of what a purebred dog is. In case the data and the way in which they measure whether or not they are a breed is not known, they cannot be pigeonholed into purebred dogs no matter how much aesthetic resemblance they have, because they will probably not do genetic controls on all dogs.

At the Veterinary Congress that took place in Malaga in 2017, some of the cons of castration were exposed, which can cause: osteosarcoma, prostate carcinoma, hemangiosarcoma, lymphoma and lymphosarcoma, mast cell carcinoma, transitional cell carcinoma, urinary incontinence, resistant urinary tract infection, immaturity of the genital organs, surgical risks, orthopedic alterations, various immune diseases, vaccine reactions, hypothyroidism, progression of cognitive dysfunction syndrome and, importantly, fear, as a behavior, can be increased. In addition to these conclusions of the Veterinary Congress of Malaga, the congress (Málaga [39]) International Association for Defense Canine and his Responsible Owners (IADCRO), where reasons against castration were also detailed. In a study published by the Scientific Information and News Service (SINC) and the research team of the University of Cordoba (UCO), the external and inherent factors in dogs are shown in order to understand aggressiveness, and among all of them, there are that, according to Joaquín Pérez-Guisado, lead author of the study, it is found that the castration of females is a factor that increases or causes aggressiveness and not the other way around. In the wake of fear, another study concluded that castration is not the solution to the behavioral problems of fear; in fact, it appears that castration influences fears of fireworks. In another study, where rottweilers were analyzed, it was concluded that aggressiveness in neutered females was higher than in unneutered females and that there was hardly any difference between neutered males and whole males.

Everything seems to point to aggression having some kind of relationship with serotonin. The lower the serotonin, the greater the aggressiveness and vice versa, likewise, the amount of protein in the diet can also influence, since protein helps to increase tryptophan, and this is directly related to serotonin; The more tryptophan, the more serotonin, the more serotonin, the less aggressiveness, it should be noted that an excess of serotonin can also cause some diseases, such as pulmonary hypertension. Cortisol also influences aggressiveness, being proportional: the higher the cortisol index (a fact that seems to occur with castration [see next page in the paragraph on (Pérez Guisado, et al. [40-46]) the greater the aggressiveness. Many other factors influence, as well as many other body chemicals to determine aggressiveness in a dog and it cannot be summarized with two types of hormones, since, for example, serotonin also influences fear, as well as there are different uses for different hormones, it has even been possible to verify cases of dogs that suffered from physical ailments, such as otitis, which degenerated into behavioral problems (Belén Rosado, et al. [47-51])

A study concludes that both joint problems and some cancers are generated in neutered dogs. The study in question was carried out on two specific breeds: golden and labrador retriever. Another study also showed that castration had an increased risk in males and females to develop cancer: hemangiosarcoma, hyperadrenocorticism, lymphoma, mast cell tumor and osteosarcoma, as well as anterior cruciate ligament rupture and epilepsy. Likewise, it has also been found that there is a greater risk of capital physeal fractures and secondary femoral neck fractures and metaphyseal osteopathy in neutered cats. The different types of cancers investigated: prostate carcinoma, transitional cell carcinoma of the bladder, prostate and prostate adenocarcinoma, increase the risk of appearance in neutered dogs. Likewise, a study carried out on 1,170 German shepherds showed that there were more joint problems in neutered males than in unneutered males (21% - 7%); in neutered females than unneutered (16% - 5%). These joint problems also came from performing early castrations before one year of age. Urinary incontinence was not diagnosed in unneutered females, while in neutered females before one year of age it was diagnosed in 7%. In addition, breast cancer was diagnosed in 1% in neutered females and in 4% in unneutered, what this study showed, contrary to popular procastration opinions, is that neutering does not prevent female dogs from suffering from breast cancer, it only reduces the probability, although not drastically. As a result of castration in puppies, there is another study where five diseases were analyzed in golden retrievers, this study concludes that if castration is done early, there is a greater chance of suffering from the following diseases: hip dysplasia (HD), cranial cruciate ligament (CCL) tear, lymphosarcoma (LSA), hemangiosarcoma (SAH) and mast cell tumor (MCT). Patients were classified as intact, neutered early (<12 months) or late (> 12 months). Statistical analyses involved survival analyses and incidence rate comparisons. Results are reported at the significance level of 5%. Of the newly neutered males, 10% were diagnosed with HD, twice as often as in intact males.

There were no cases of CCL diagnosed in intact males or females, but in males and females with early castration the occurrences were 5 and 8%, respectively. Almost 10% of newly neutered males were diagnosed with LSA, (L Hart, et al. [52-56]) three times more than intact males. The percentage of SAH cases in females with late castration (about 8%) was 4 times higher than that of intact females with early castration. There were no cases of MCT in intact females, but the occurrence was nearly 6% in females with delayed castration. The results have implications for the health of dogs that are used as assistance and for oncologists who use dogs as models of cancers that occur in humans. One article explained that the associated joint disorders, cancer and urinary incontinence, could be caused by castration. Sterilization directly affects urinary bladder function, is currently incurable, and results in urinary incontinence in neutered females. Everything seems to point to a problem with the bladder wall, as well as a high percentage of collagen in castrated females (LH and GnRH receptors are affected).

There is evidence that neutering is associated with an increased risk of urinary incontinence, to the point that the sooner a dog is neutered, the greater the risk of incontinence, it can also occur in cats, although more studies are needed due to the lack of information on the subject, there is some drug that can be administered to control incontinence (effective between 50% and 88%), as is the case of Propalin, which contains an active ingredient (Torres de la Riva, et al. [57-68]) Fenilpropanoarranged Used in anti-flu products for humans, however, this type of product can be too expensive to administer daily to the dog suffering from this disease, so its constant use for life may not be feasible. According to the product sheet, it should be administered 1 mg/kg (0.1 ml/5 kg) 3 times a day, which means for a 5 kg dog an expense of 1 bottle per year (of 100 ml [100 ml / 0.1 ml = 1,000 / 3 (daily doses) = 333 days of medication]), however, in 60 kg, the cost would amount to 13 bottles per year [60 / 5 = 12; 12 x 0.1 ml/time = 1.2 ml x 3 (dose daily) = 3.6 ml of product per day; 100 ml / 3.6 = 27.7 days]. The average price of this product is 41 euros for a 100 ml bottle (farmaciadelicias.com, 09/2022). Canine urothelial carcinoma is also associated with neutering, which is the common cancer of the lower urinary tract in elderly spayed female dogs (AEMPS [69,70]) It is estimated that neutered animals have a longer life, although this data is biased. Some studies have been based, simply, on studying when individuals die and not in the why, except for one study, which showed that castration decreased the risk of death from some causes, such as infectious diseases, but increased the risk of death from others, such as cancer. It was interesting to note that the study was divided into the 4 types of dogs by size: small, medium, large and giant, since it is already known that small dogs have a greater longevity than larger ones, showing as a result that sterilization increased the risk of neoplasia in small breeds; In the same way, an economic factor is associated in the problem of infections and that is that they attribute that owners who cannot afford the cost of sterilization, may also lack the resources to provide medical care for infectious diseases that could come later, resulting in dogs that can access better medical care, They can live longer, although this factor was not necessarily decisive in the study in question (Hoffman, et al. [71]).

In various studies it was concluded that sex steroids perform a very important function on the autoimmune system. Castration reduces the plasma concentration of 25-hydroxycholecalciferol, an essential molecule in the synthesis of vitamin D and whose low concentration is associated with more tumours, both in humans and dogs. Castration is associated with an increased risk of certain autoimmune disorders: atopic dermatitis (ATOP), autoimmune hemolytic anemia (AIHA), hypoadrenocorticism (ADD), hypothyroidism (HYPO), immune- mediated thrombocytopenia (ITP), inflammatory bowel disease (IBD), lupus erythematosus (LUP). Suppressor and cytotoxic T cells appear to have a very important role in killing cancer cells, and therefore there may be a direct relationship between the elimination of gonadal steroids and the alteration in the ability to recognize and destroy these precancerous cells, resulting in physiological tolerance for the proliferation of the various cancers. Female hormones are also known to control development, homeostasis, gene expression and signaling processes in T and B lymphocytes to influence their health function and disease. There is also a relationship in the appearance of autoimmune diseases, such as rheumatoid arthritis or osteoporosis, when the ovarian production of sex hormones decreases. These same sex hormones are implicated in cardiovascular protection, including healing in the event of arterial injury (Selting, et al. [72-75,28,76-79]).

There are studies that suggest that castration can influence the increase in the development and progression of cognitive dysfunction syndrome, a neurodegenerative disorder, affecting especially females, this is related to estrogens, as they seem to be protective against brain aging and the growth of brain tumors in dogs. In all animal species there are estrogen receptors in the brain: ERα, ERβ and GPER, these receptors have a function linked to gonadal hormones, for this reason both estrogens and androgens affect verbal fluency (in humans), performance in spatial tasks (humans) and movement coordination in animals. There is also evidence that the ovaries produce (Rzechorzek, et al. [80]) estradiol (hormone of the estrogen group), a hormone that affects the development and function of the brain, so much so that some evidence has been provided that estrogen (17β-estradiol) is produced even in the testicles, which indicates the shape and size of neurons and astrocytes. There also appears to be a direct relationship between menstrual cycles and increased cognitive performance (Santoro, et al. [81-82]). In a specific study (carried out on more than 30,000 Labrador retrievers), they relate castration to being overweight, this difference being even greater between males than between females (males: 4.1% - 11.4% / females: 8.3% - 12.5%). The same study, along with another, indicated that the evidence of reduced risk of mammary neoplasia from neutering is not a solid basis for neutering dogs (McGreevy, et al. [83,64]).

The cortisol It is a steroid hormone that has direct implications with the autoimmune system. With castration there is an imbalance of cortisol that can lead to different problems at the immunological level. Paradoxically, the scenario of this study (carried out over more than 35 years) concluded that diseases caused by cortisol imbalances range from allergies to severe cases of autoimmunity to cancer, caused, above all, by an excess of estrogen. The interesting thing is that these estrogen excesses were identified in more than 90% of spayed dogs, so this pathology cannot be attributed to ovarian activity. The adrenal cortex is another main source of imbalance (it provides more estrogen to try to compensate for the loss of estrogen in the ovaries) and it seems that the results of the same study suggest that cortisone can, if not be avoided, be modified to some points. Various studies carried out in different countries and years, as well as carried out by experienced and new surgeons, have shown the increase in cortisol after ovariohysterectomy, without exception. Estrogens act as related receptors and are critical modulators of immune function, both innate and adaptive, as well as increase the production of immunoglobulins, thus improving the immune response. They also help build autoantibodies. The function performed by estrogens, in the right measure and the normal functioning of the body, is very extensive, for a more detailed list, it is recommended to read the study by doctors: (Oberbauer, et al. [28,84-87])

About psychological pregnancies (or pseudogestations) some veterinarians recommend the castration of the dog, however, there are several studies that assure that neutering does not prevent pseudogestations or, in other words, neutered dogs can also have psychological pregnancies. In any case, it must be remembered that pseudogestations involve hormonal changes, in some dog’s behavior, apathy, lack of appetite, etc., can change, but in others practically no change will be noticed except the expulsion of milk through the breasts, something that must be controlled to avoid mastitis, which points out that it is the only drawback that pseudogestations can have. This aspect is dealt with in more detail and detail in Chapter 8. (Root AL, et al. [88-92])

Another study revealed that the benefits of neutering in males were inconsistent, including that it could affect normal musculoskeletal development, causing bone elongation in the dog, and that in females it could lead to diseases such as cruciate ligament rupture, various cancers, obesity, urinary incontinence and a series of other risks, several of them already specified above. Obesity has determined to be a very important factor in shortening the life of dogs and cats (and mammals in general), where factors such as the breed to which they belong, the type of owner they have, sex, neutering status, etc. In fact, several studies link castration to obesity and obesity to the development of diabetes millitus. Neutering can increase daily food intake, decreases metabolic rate, and can decrease physical activity. Likewise, there is evidence that serum IGF-1 concentrations decrease in neutered dogs, this decrease can affect growth hormone (especially in humans).

The decrease in IGF-1 can affect insulin resistance, osteopenia, hypogonadism, intestinal alterations and even cirrhosis, it can also be related, especially in males, to the increase in testosterone, which helps to increase muscle and bone mass. (Urfer, et al. [7,28,93-99]) When it comes to dogs about their usefulness, it is known that dogs are used, above all, at the police level. A study revealed that unneutered male dogs are the best to use in drug detection, or what is the same, the dog when neutered can have loss of smell and difficulty training. It was also shown in another study that unneutered dogs are bolder than neutered dogs (F Abdel Fattah, et al. [100,101])

Other studies have revealed the relationship between oxytocin (also vasopressin), cognitive processes, the relationship with humans and other dogs, as well as aggressiveness and it is interesting to know that unneutered dogs show better responses to oxytocin than neutered dogs, likewise, some experiments have been done on rats that have resulted in oxytocin varying with reproductive cycles, which means that in the same will happen and it was also shown that the assimilation of oxytocin is regulated by estrogens, it is even known that the same neurophyseal hormone is important in lactation, childbirth and central nervous system involved in sex, maternal behavior and the control of heart function. It also influences cortisol, as it seems that the higher the cortisol (caused by castration), the less oxytocin (MacLean, et al., [102-110]).

It was also concluded by the study carried out in Italy over 15 years on “Behavioral and physiological indicators of dog welfare in shelters (Cafazzo [111]). The text contained in the WSAVA continues: (VVAA, [112]). However, utilitarian views on sterilization are part of a possible solution to the larger problem of pet overpopulation, although it can result in individual pain and risks. If there are no reasonable alternatives, preventing unwanted animal births could better ensure the welfare of human and animal populations. Which means that, if an owner is responsible for the care of his animal (to avoid pregnancies and if there are any, take care of them with dignity and responsibility, either by looking for a home or keeping them), it makes no sense to neuter them. It is important to review the entire clinical picture of each specimen, to have all the information available to make the best decision possible and not to be carried away by commercialism, or by opinions without scientific rigor of different associations, as well as by fashions, internet forums or social networks. It is clear that sex hormones play a very important role in the functioning of each dog, each animal, each living being, not only because of the immune system, which is responsible for protecting the animal from everything around it, but also to protect itself from other pathologies. All these studies carried out on dogs have been corroborated in a similar way in cats, since obesity is one of the factors inherent to neutering in cats, as well as the probability of developing diabetes militus. Similarly, there is evidence that castration affects the vaginal mucosa and the microbial community that colonizes the vaginal tract. (Öhlund, et al. [95,113-116])

There is a lot of controversy with castration. Different ideological currents and different economic interests are the ones that tip the balance to one side or the other. What is true is that science shows more and more, with larger studies, that neutering has many drawbacks and problems for the health of dogs. The main reason for being in favour of neutering is expressed by animal protection associations, alleging that animal abandonment must be fought, something that has been proven not to work and that there are other more effective and cheaper methods to prevent abandonment, especially when the main reason for animal abandonment in Spain is not, precisely, having unneutered animals, or unwanted litters, but rather economic problems, which include: behavioral problems (for not being able to pay trainers or educators), change of address (for going to rental places where they do not accept animals, for example), loss of employment, unspecified economic factor... Thus, it could be taken into account, for example, the elimination of tax obstacles to the possession of an animal, such as VAT, not only in the veterinarian (medicines are taxed at 10% and the substances to obtain these medicines at 21%, as are cosmetics and other products...), but in everything related to the same, such as the purchase of feed, toys for them, restraint systems for vehicles, aid to hotels so that they do not charge extra for bringing pets and a long number of other options that affect animals and their maintenance, at an economic level. And, to this, you can add the collection of a fee or tax in different municipalities for registering the animal in the registry of ceased pets. (Agencia Tributaria [117]).

Neutering has some pros, however, there is increasing evidence that it has more cons. The amount of prejudice that exists with any type of sterilization, whether in dogs or cats, should be assessed individually and never taken as a standardized norm. It makes no sense that there are laws that are based on rights, welfare, etc., and something as simple as maintaining the correct development of the animal, with the sexual organs intact, is not allowed, especially when it comes to the purchase and sale of animals in animal protection associations, since one of the pillars that they themselves defend and claim to promote is, precisely, animal welfare. Usually, the benefits that an animal could have are always shown: behavioral problems, avoiding urination, avoiding mounting, avoiding some cancers and some infections, which, although they have their part of reason, some of them are questionable, when the owner makes it go through the operating room, even if there is no medical need, however, scientific evidence contradicts what is politically correct. It seems that only a few are the right ones to talk about ethics and that all animals are good for amputating their sexual organs, but nothing could be further from the truth.

The good intentions that may exist behind these surgical or chemical actions are not always positive for animals. Likewise, the number of possible diseases caused by castration are many, such as: different cancers, urinary incontinence, various infections, surgical risks, obesity, fractures, neurological, growth, cognitive problems... All the possible cons that are located when performing a castration should be thoroughly examined, both by the professionals who advise, and by the owners who may suffer the care of their animals once they suffer from them, for example, if their dog is healthy and when castration is performed, urinary incontinence is caused, he must be aware of the care he requires and assume this problem that he has generated for his own animal. Neutering should be examined individually in each case, as indicated above. Apparently and from a medical and health point of view, that is, without a justified medical reason it makes no sense to neuter a canine, it even makes no sense to claim “animal welfare” to perform a castration. In different cases, tests could be carried out with chemical sterilizations to check if surgical sterilization is the solution, although this also has some contraindications. So much so, that special mention must be made of the WSAVA (World Small Animal Veterinary Association) where it says the following:From the point of view of animal rights, sterilization restricts the rights of animals to reproduce, and since the animal itself cannot consent to the procedure, castration cannot be tolerated (...) (VVAA, [112], pág. 59).

It has been possible to verify the number of harmful effects that exist when any animal, including humans, lacks the sex hormones necessary for the proper development and maintenance of the individual. It seems incredible that such a commonly known hormone can deter cognitive development, obesity or even ligament fractures, because it is related to the absorption of vitamins, as necessary as D (although it is possible that other factors influence, but perhaps this hormone is the main one). It is interesting to know that there are hormones that control the simple transit and development of the entire digestive system, as well as that a set of hormones (together with a gene) are the triggers of all the growth of each individual, designating the sex by which their body should be guided and its correct maturation, until reaching adulthood. Evolution that will even mark the possible development of certain diseases or some inclination that has to do even with the racial group to which he belongs. Likewise, it is important to understand that this correct development can be truncated by those who claim to love them, as long as they create laws that condition the growth of any dog or cat that is in a country where the laws are not made by professionals and that it seems that there is less and less room for science, studies, etc. R+D and more room for sentimentality, which, as has been verified, only leads to the malformation and destruction of every animal that inhabits the earth. There is also a controversy regarding pseudopregnancy. Scientific evidence has shown that, in both neutered and unneutered females, this hormonal condition can occur. (Fernández Martín, et al. [118-121]) Everything related to cats and dogs (in general, animals) must be treated in a professional way and, necessarily, there must be room for experts who are dedicated to the sector. Likewise, the development of the legislation that will modify and mark the lives of both owners and pets should be a similar issue. Something important, also to take into account, is that there is still a lot of research to be done, since more financial aid should be allocated to finance research projects and studies on topics as important and necessary as castration. Even this article is subject to receiving updates from new studies that come out over the years.

The data presented throughout this article is part of several books authored by the same author, this article has been updated and expanded. The sources are from different open access websites, the Affinity Foundation, Pubmed and others are publicly available, although some articles are paid.

FJFM certifies that it has no affiliations, nor participation in any organization or entity with any financial interest related to this article, nor does it have a non-financial interest in the subject matter or materials discussed in this manuscript.

This article has been made free of charge without expecting financial compensation, and has not been financed by third parties, companies, individuals, or associations. Likewise, the original language of the article is Spanish from Spain.

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