From the most common veterinary surgical textbook:
An estimated 3 to 4 million dogs and cats are euthanized each year at US humane shelters alone.45 To prevent unwanted pregnancies, most veterinarians in the United States recommend elective gonadectomy in dogs and cats at 6 to 9 months of age, with females spayed before first estrus to decrease the risk for mammary cancer.94,99 There is little scientific evidence to support that 6 to 9 months is the optimal age for neutering.93,94 Early neutering (8 to 16 weeks) is endorsed by the American Veterinary Medical Association (1993, Resolution 6), American Humane Association, Humane Society of the United States, Society for the Prevention of Cruelty to Animals, Society for Theriogenology, and American College of Theriogenologists.54,93,112 Despite these endorsements and multiple studies to demonstrate little short- and long-term risks to patients, some veterinarians are reluctant to neuter patients at an early age. Special anesthetic and surgical recommendations for prepuberal patients include withholding food 3 to 4 hours before surgery, decreasing dosages of medications, adding dextrose to surgical fluids, and monitoring for clinical signs of hypoglycemia.43,44,95 Application of an inguinal tattoo in prepuberal patients will help identify those that have undergone early gonadectomy.44
Concerns have been raised about effects of early age neutering (including ovariohysterectomy) on joint disease and neoplasia in dogs.34 Based on short- and long-term studies of dogs and cats, gonadectomy at early ages (<24 weeks) does not increase morbidity, mortality, musculoskeletal disorders, genitourinary disorders, gastrointestinal disorders, obesity, or physical/behavioral problems compared with animals gonadectomized at later ages.41-44,104 Cats neutered at 7 weeks and 7 months had no difference in radial length; both groups had delayed distal radial physeal closure compared with intact male cats.95 Male cats neutered at 7 weeks and 7 months are heavier than intact cats; however, neutered and intact cats have the same level of activity.101,106 Early neutering has no effect on urethral diameter or urethral pressure profiles.44,107 Cats neutered before 5.5 months of age have a lower incidence of urinary tract infections than those neutered later.41 An early study by Herron39 in 1971 documented preputial adhesions in 4 out of 10 cats neutered at 5 months of age. In a more recent study of cats neutered at 7 weeks and 7 months, no preputial adhesions were found.106
Canine castration serves as a treatment, preventative, or adjunct treatment for perianal adenomas, prostatic abscesses, prostatitis, benign prostatic hyperplasia (BPH), prostatic cysts, and sex hormone–associated alopecia.27,118 Perianal (circumanal) adenomas are hormone dependent, and neutering without perianal adenoma resection will often result in regression of the tumor. Excision is recommended only for recurrent perianal adenomas, ulcerated tumors, or perianal tumors of other causes (carcinoma, squamous cell carcinoma, and sebaceous gland adenocarcinoma). In addition, testosterone may be a factor in the development of perineal hernias.118 After bilateral orchiectomy, plasma testosterone levels will decrease within 2 to 12 hours in dogs and 24 to 96 hours in cats and will remain low.84,110 In cats, castration results in rapid postoperative decline in fighting, roaming, and urine spraying in 53%, 56%, and 78% and a gradual decline 35%, 38, and 9%, respectively.33 Castration will not decrease the risk for prostatic cancer, because many prostatic cancers are androgen independent.9
Despite hormonal decreases, castrated dogs reportedly have as increased risk for bladder and prostate cancer compared with intact males.9 In addition, Cooley et al.12 found that Rottweiler Dogs neutered before 1 year of age had increased risk for developing osteosarcoma. Torres de la Riva et al. reported an increased risk for lymphosarcoma and joint disease in Golden Retrievers castrated before 12 months of age, as compared with intact males.113 Hart et al. noted that castration at < 6 months of age doubled the incidence of joint disease in Golden Retrievers.34 Caution should be used when critically evaluating such studies because the cases in some studies9,12 were drawn from secondary and tertiary veterinary referral centers, which may not represent the canine population at large. These finding should be replicated in primary general practicing centers in a variety of socioeconomic regions and also weighed against the multiple advantages of castration.
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