There is debate about early neutering and growth plate closure in dogs. A great article that covers all of the aspects of neutering is: http://www.wolftucker.co.uk/blog/neutering-your-dog-making-an-informed-decision/.
This blog is on how neutering may affect growth plate closure in dogs. Neutering removes the reproductive organs and thus reduces or eliminates the production of certain hormones such as testosterone and estrogen. Male and female sex hormones are known to play key roles in the closure of the epiphyseal plates and as such will affect skeletal development.
Disruption of the function of the growth plate may lead to anatomic deformity and secondary conditions such as degenerative joint disease and osteoarthritis. Some factors that may affect the epiphyseal growth before closure include diet, environment, trauma and neutering (Lewis, G. 2019).
Malnutrition can result in stunted growth and obesity, can increase the load on joints and may lead to malformation of the epiphysis. The environment in which the puppy is reared may also affect growing bones. With potential damage being caused to the underdeveloped epiphysis with stairs, slopes, over exercise or uncontrolled exercise. Adolescence and sexual and skeletal maturity are normally reached between six and twenty-four months (Lewis, G, 2019).
Neutering is the removal of reproductive organs and will result in a decrease in gonadal steroid and hormone production (Lewis, G. 2019). According to Dr Mark Elliot BVSc (2017) in the UK neutering is carried out, in bitches, routinely before their first season. Neutering, he reports, may be performed for convenience, population control, behavioural benefits, protection of bloodlines and potential health benefits.
Decisions as to whether neutering should be carried out and if so at what age are completed by dog owners with varying levels of knowledge of the benefits and risks. These decisions can be made even more complex with conflicting advice and with little observance of current research.
Hip dysplasia is one of the most common orthopaedic problems in dogs. (Witsberger et al., 2008). It is a developmental condition that involves a lack of conformity between the femoral head and the acetabulum which results in instability of the hip joint. It is thought to be largely due to genetics with larger breeds being more prone than smaller breeds. An excessive growth rate, certain types of exercise, obesity and an imbalanced diet may also contribute. It is also notable that in a study of 759 Golden Retrievers, hip dysplasia was more than doubled in the male neutered population with a significant difference demonstrated between early to late neutering. This risk was not altered in females. (Torres de la Riva et al., 2013). In another study of 1,500 Labrador Retrievers, there was no difference demonstrated between male intact and neutered dogs though in females the risk was higher for those spayed up to 2 years old compared to intact females. Those spayed between 2 and 8 years old had no incidence of hip dysplasia. (Hart et al., 2014). It has also been noted that neutered dogs tend to gain weight, another factor considered to contribute to hip dysplasia (Howe, 2015).
Cranial or anterior cruciate ligament disease (CCLD) is said to be the leading cause of lameness and stifle osteoarthritis in dogs (Witsberger et al., 2008 as cited in Alvarez et al., 2022). The reasons for the rupture of the ligament are largely unknown but are thought to be linked to progressive degenerative joint disease with a multifactorial background and consequential ligament failure. A recent study (Niebauer and Restucci, 2023) looking at the etiopathogenesis of CCLD suggests that ‘biomechanics, joint conformation, blood supply and joint metabolism, as well as body weight and muscular envelope’ may all factor in final structural failure. Other risk factors such as ‘genetics (breed), sex, neuter status, and obesity’ are involved as well (Niebauer and Restucci, 2023). One study looking at larger dogs felt that the altered biomechanics may be attributed to an excessive tibial plateaux angle. The dogs with an excessive tibial plateaux angle were 3 times more likely to have been neutered before 6 months of age, reporting that ‘early neutering was a significant risk factor for the development of an excessive TPA in large breed dogs with CCLD’ (Duerr et al., 2007). Witsberger (2008) also found that neutered dogs were significantly more likely to have CCLD. Golden retrievers were found to have a significantly higher risk of Cranial cruciate ligament ruptures in both male and female canines following neutering before 1 year of age (Torres de la Riva et al., 2013). This has been corroborated in numerous other studies suggesting that neutering plays a role in the incidence of canine cruciate ligament rupture (Howe, 2015). In many of these studies it is not known if the dogs may have been overweight, with questions as to whether the increased weight in the large breeds may have affected the epiphyses during growth however, Torres de la Riva et al., (2013) found no difference in Body Condition Score between the dogs with and without CCLD suggesting that neuter status is more significant than weight.
Elbow dysplasia typically affects medium to large, rapidly growing dogs. It is related to abnormal bone growth, joint stresses or cartilage development. In puppies, either one or both of the elbow joints may start to grow incorrectly. An ununited Anconeal process results where there is the separation of the ossification centre of the anconeal process from the proximal ulnar metaphysis. In Fragmentation of the Medial Coronoid process, the coronoid process fails to unite with the ulnar diaphysis. Osteochondrosis of the medial humeral condyle results from a disturbed endochondral fusion of the epicondyle with the distal end of the humerus (Harari, 2020). It is reported that it is hereditary though diet, exercise and the environment of the mother whilst pregnant may also have an effect (Loconti, 2021). This considered, a higher incidence of elbow dysplasia was noted in male Labrador retrievers castrated before 6 months of age, though no difference was seen in female Labrador retrievers. (Howe, 2015).
Obesity, with increased weight on the growing epiphyses, may play a role in CCLD and hip dysplasia (Vendramini et al., 2020). Elbow dysplasia generally affects larger breeds (Harari, 2020) therefore, the increased weight on fast-growing epiphysis may also be a contributing factor. It is reportedly well-known that following neutering animals tend to gain excessive weight (Vendramini et al., 2020).
Spaying can significantly increase the rate of the dog developing varying degrees of incontinence with between 12 and 20 per cent of bitches having incontinence around 2-3 years later. Neutering in a prepubescent dog under the age of 5.5 months may also account for an increase in perivalvular dermatitis and cystitis (Howe 2015). This information must be weighed up against the knowledge of the reduction in mammary cancer in female dogs and the total prevention of Pyometra. (Vazquez et al., 2023) and the elimination of testicular neoplasia in male dogs (Elliot 2017).
In prepubescent dogs, neutering has been demonstrated to delay the growth plate closure compared to intact dogs. It must be noted that delay of the closure of growth plates may lead to elongated long bones, and altered function of muscular anatomy therefore, predisposing dogs to muscle, tendon and ligament injuries and calcification (Salmeri et al., 1991).
Although current information around the most common orthopaedic problems in dogs does not often report neutering as a factor; diet, exercise and breed are most often reported, the high incidence of these concerns in the early neutered population as opposed to the late neutered, or intact population, across numerous studies, demonstrates that the timing of neutering should be considered carefully and that neutering of the dog once skeletally mature may arguably be the best option.
コメント