Spaying or neutering doesn’t just prevent pregnancy. From metabolism and weight changes to behaviour and long-term health, a veterinarian explains how hormonal shifts after sterilisation quietly reshape a pet’s body.
Sterilisation is commonly discussed as a solution to prevent unwanted litters, but its impact on a pet’s body goes far beyond reproduction. When dogs and cats are spayed or neutered, the removal of reproductive organs leads to major hormonal changes that affect metabolism, growth, behaviour and overall health. These changes tend to unfold gradually, and many pet parents may notice subtle differences weeks or months after the procedure without fully understanding the cause.
Hormones such as oestrogen, progesterone and testosterone play a crucial role in regulating appetite, energy levels, bone development and stress responses. After sterilisation, the sudden decline in these hormones can alter how a pet’s body processes calories, responds to physical activity and regulates emotional states such as anxiety or arousal.
Understanding these hormonal shifts is essential for responsible pet care. With timely adjustments to diet, exercise and daily routines, many of the unintended effects of sterilisation can be managed effectively — and in some cases, prevented altogether.
Which hormones are affected after sterilisation?
Dr Deepraj Prajapati, senior veterinarian at RD Pet Hospital, Ambedkar Nagar, explains: “The most significant hormonal change after sterilisation is the reduction of sex hormones — oestrogen in females and testosterone in males. These hormones do much more than regulate reproduction. They also influence metabolic rate, muscle mass, fat distribution and appetite control.”
As hormone levels drop, many pets experience a natural slowdown in metabolism, meaning they burn fewer calories than before. If food intake remains unchanged, gradual weight gain may follow. Over time, excess weight can increase the risk of joint problems, diabetes and cardiovascular disease.
At the same time, lower levels of sex hormones significantly reduce the risk of hormone-related conditions such as mammary tumours, uterine infections, testicular cancer and prostate enlargement — offering important long-term health benefits.
How hormonal changes influence behaviour
Sex hormones also play a key role in behaviour, particularly mating and territorial instincts. Dr Prajapati notes that reduced testosterone in male dogs and cats often leads to decreased roaming, urine marking and hormone-driven aggression. In females, the absence of heat cycles can reduce restlessness, vocalisation and mood fluctuations.
“In many cases, these hormonal changes result in calmer and more predictable behaviour,” he says. “However, sterilisation does not eliminate learned behaviours or alter a pet’s core personality. Anxiety, fear-based aggression or behavioural issues rooted in early experiences may still require training, environmental enrichment or professional behavioural support.”
Lifestyle adjustments pet parents should consider
Rather than waiting for problems to arise, pet parents should adopt a proactive approach after sterilisation, Dr Prajapati advises.
“Diet is the first area that usually needs adjustment,” he says. Portion sizes may need to be reduced, or pets may benefit from nutritionally balanced, sterilisation-specific diets designed to support a slower metabolism.
“Regular, age-appropriate exercise is essential to maintain muscle mass and prevent fat gain. Mental stimulation through play, training and enrichment is equally important, as reduced hormone levels do not eliminate a pet’s need for activity and engagement. Routine weight monitoring and veterinary check-ups help identify subtle changes early, allowing timely interventions that support long-term health and wellbeing.”
