Surgical sterilisation of companion dogs including ovariectomy, ovariohysterectomy, and castration is often referred to as spaying, neutering or desexing. This is the common approach to preventing overpopulation of unwanted dogs.

However, surgical sterilisation has been linked to an increased incidence of health conditions that affect a dog’s musculoskeletal system and their ability to participate in physical activity.

Anatomy of the dog’s reproductive system

Mammals’ reproductive systems are complex and closely linked to the endocrine system namely the hypothalamus and pituitary gland. The hypothalamus secretes the gonadotropin-releasing hormone. This hormone stimulates the pituitary gland to release luteinizing hormone (LH). The luteinizing hormone stimulates the dog’s reproductive organs to produce gonadal steroid hormones. In males, testosterone is produced and in females estrogen / progesterone. These hormones provide feedback to the hypothalamus and the pituitary gland to decrease the secretion of gonadotropin-releasing hormone and luteinizing hormone.

In dogs that have been surgically sterilised, the feedback loop from the reproductive organs is not available so the concentrations of luteinizing hormone in the dog’s body increases. In sterilised dogs, LH levels can be more than thirty times that of entire animals.

While the main function of LH is reproductive, there are LH receptors in non-reproductive tissues too. Non-reproductive tissue where LH receptors have been found in mammals include the adrenal cortex, blood vessels, brain, fibroblasts, gastrointestinal tract, lower urinary tract, lymphoid tissues, skin, muscle tissues and thyroid gland.

With constant activation following sterilisation, the LH receptors in non-reproductive tissues are upregulated which heightens the effects of high concentrations of LH on these tissues.

Desexing and weight gain in dogs

Sterilisation affects the dog’s appetite and metabolic rate, both of which can lead to obesity. In entire dogs, gastrointestinal hormones that create a feeling of fullness are secreted after food intake. In several studies, one week after sterilisation food intake could increase up to 20% and persist at these levels. It is hypothesized that LH receptors in the gastrointestinal tract that are upregulated after sterilisation, suppresses the release of hormones that signal to the dog that they are full.

Sterilisation also decreases the dog’s daily energy requirements. The mechanism for this decrease is unclear however combined with the increased appetite, weight gain is likely unless food intake is restricted.

Obesity in dogs, like humans, leads to reduced physical activity and other chronic health conditions.

Desexing and joint problems in dogs

Increased concentrations of LH in sterilised dogs has been linked to greater incidence of musculoskeletal conditions including hip dysplasia and cranial cruciate ligament rupture.

Most dogs that develop hip dysplasia are born with normal hips and develop the condition as they age. In giant and large breed dogs, the incidence of the condition can be as high as 83%. Compared to entire dogs, the incidence of hip dysplasia in sterilised dogs increases by 1.5 to 2 times. While the reason for this difference is unknown, it is proposed that the activation of LH receptors in the tissues supporting the hip joint may play a role.

Sterilisation also increases the prevalence of cranial cruciate ligament rupture. One study found a doubling of the incidence of CCL rupture in desexed dogs compared to entire animals. In pre-pubertal dogs, sterilisation delays the growth plate closure which increases the length of the tibia and the steepness of the tibial plateau. The steepness of the tibial plateau increases cranial forces on the cruciate ligament which increases the risk of injury.
Even when desexing is delayed, the risks of CCL are greater in sterilised dogs than entire ones. It is thought that ligament laxity may be related to the hormones estrogen and relaxin however the role of activated LH receptors should also be considered a risk factor.

While sterilisation is an effective way of controlling the number of unwanted puppies, it’s long term effects on dogs’ health and ability to partake in physical activity should also be considered.

Full Stride provides remedial canine massage treatments to keep dogs active and healthy.

Until next time, enjoy your dogs.

Sources:

Khawla Zwida and Michelle Anne Kutzler 2016 “Non-Reproductive Long-Term Health Complications of Gonad Removal in Dogs as Well as Possible Causal Relationships with Post – Gonadectomy Elevated Luteinizing Hormone (LH) Concentrations.” J Etiol Anim Health 1: 002.

Leclerc, L, Thorin, C, Flanagan, J, Biourge, V, Serisier, S & Nguyen, P. 2017 “Higher neonatal growth rate and body condition score at 7 months are predictive factors of obesity in adult female Beagle dogs” BMC Veterinary Research 2017 13:104