23/07/2024
The below is copied from "Good Dog Ownership" page :
Spay/ neutering is the most frequently performed elective veterinary surgery (estimated prevalence of >60% in dogs and cats) in the United States and is commonly recommended for population control as their shelters are overloaded, reduction of hormonally driven behaviours which doesn't always work , disease treatment or prevention, and sadly pet owner convenience.
In the United States, canine gonadectomy has traditionally been performed at ≈4 to 6 months of age, after puppies complete their long vaccine series (US).
From a surgeon's perspective, surgery at this age or younger is easy, fast, and safe because of small patient size, lack of body fat, and rapid recovery; however, recent studies suggest gonadectomy before skeletal maturity can have adverse effects, particularly in certain dog breeds.
More owners and clinicians are thus reconsidering their opinions on timing of gonadectomy and whether it should be performed.
According to a Swedish insurance study of >260,000 female dogs, mammary tumours were most often reported in Leonbergers, Doberman pinschers, Bernese mountain dogs, Welsh terriers, English springer spaniels, American cocker spaniels, and boxers. For each of these breeds, the estimated likelihood of developing mammary tumours over a lifetime was ≥35%; conversely, estimated likelihood was ≤5% for basenjis, collies, Finnish Lapphunds, Lancashire heelers, Norwegian Buhunds, Norwich terriers, Pomeranians, pugs, and Siberian huskies.
In another study of >7,000 female dogs in the United States, no mammary cancers were reported in intact or gonadectomized Bernese mountain dogs, boxers, miniature schnauzers, pugs, Saint Bernards, Shetland sheepdogs, or West Highland white terriers, but a high incidence was reported in American cocker spaniels and English Springer Spaniels. Based on these studies, owners of cocker spaniels and English springer spaniels may be counselled to consider spaying before the first or second oestrous cycle; however, mammary cancer may not play a decision-making role for owners of West Highland white terriers or Shetland sheepdogs.
The discrepancy regarding Bernese mountain dogs could reflect differences in regional genetics or follow-up: the study of Swedish dogs followed patients to 10 years of age, whereas in the US-based study, mean age at follow-up was