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Reproductive Health in Dogs

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • Pyometra is the most serious problem in unspayed females, and an emergency.
  • Pus-like discharge from the vulva or penis always needs a vet.
  • A penis stuck outside the sheath is an emergency.
  • Older unneutered males very often develop an enlarged prostate.
  • Spay and neuter timing depends on size and breed, so decide it with your vet.

Table of Contents

Research Comparison Females Males Spay and neuter FAQ Sources

Reproductive Health Quicklinks

Reproductive Health Dog in Heat Pyometra Pregnancy Spaying Neutering Penis Problems Swollen Vulva Testicular Cancer Prostate Cancer

Reproductive problems in dogs depend mostly on sex and on whether a dog is spayed or neutered. In unspayed females, the most serious is pyometra, a uterine infection that usually appears in the weeks after a heat and can be fatal without prompt treatment.1,2 Other common problems include vaginitis, vaginal swelling during heat, false pregnancy and mastitis.1 In males, common problems include retained testicles, an enlarged prostate in older unneutered dogs, sheath infections and testicular tumors. A penis stuck outside its sheath is less common but is an emergency.3,4 Spaying and neutering prevent several of these problems but carry trade-offs of their own, so the timing is worth discussing with your vet.5,6

Go to a vet now if your dog has:

  • An unspayed female who is lethargic, drinking a lot, vomiting or off her food in the weeks after a heat, with or without a discharge or swollen belly. This can be pyometra.2,1
  • A penis that is stuck outside the sheath, or looks swollen, dry or dark3,7
  • Strong straining in labor for 30 to 60 minutes with no puppy, or a green discharge before the first puppy8,9
  • A nursing mother with restlessness, stiffness, trembling or seizures. This can be eclampsia.10

See your vet soon for:

  • Any pus-like or bad-smelling discharge from the vulva or penis11,12
  • Blood from the penis or in the urine13
  • A lump on a testicle or mammary gland, or a testicle that hasn't come down by about 4 months14,15

What the Research and Guidelines Say

  • Pyometra is common in unspayed females. Swedish insurance studies found it in about 1 in 5 to 1 in 4 unspayed females by age 10, and in over half of females in some breeds.16,17,18
  • Prostate enlargement is almost universal in older intact males. It affects about 80% of dogs over 6 and 95% over 9.19,3
  • There's no single right age to spay or neuter. US guidelines suggest about 6 months for small dogs and waiting until growth stops for large breeds, and UK vets now advise waiting until about 12 months or later.6,20,5
  • Spaying prevents pyometra and, when done before the first heat, greatly lowers the risk of mammary cancer.21,15
  • Mammary tumors are common in female dogs. A 2023 UK study found about 1 in 50 female dogs had a mammary tumor recorded in a year, with Springer and Cocker Spaniels, Boxers, Staffordshire Bull Terriers and Lhasa Apsos at higher risk. Spaying was linked with lower odds.22

Common Reproductive Problems in Dogs

ProblemWhich dogsMain signsHow urgent
PyometraUnspayed females, usually middle-aged or older, weeks after a heat23,2Pus discharge or swollen belly, thirst, lethargy, vomiting1Emergency
VaginitisPuppies before their first heat, and adult females, usually spayed24,25Sticky discharge, licking24Usually not urgent
Vaginal overgrowth (prolapse)Young unspayed females in heat26Pink or red tissue sticking out of the vulva1,27See a vet soon
False pregnancyUnspayed females 4 to 9 weeks after heat28Nesting, milk, mothering toys28Usually passes in 2 to 3 weeks
MastitisNursing mothers29Hot, swollen, painful mammary gland29Urgent if the gland darkens or she's unwell
ParaphimosisMales, often after arousal or mating30Penis stuck out, swelling, drying30Emergency
Sheath infectionMature males3Heavy yellow-green discharge, licking12Usually mild
Prostate problemsOlder unneutered males3Blood in urine, straining to pass stool3See a vet. An abscess is urgent.
Testicular tumorsOlder unneutered males and dogs with retained testicles4,14A lump, or enlarged nipples4See a vet
Retained testiclePuppies14A testicle missing from the scrotum14Neutering advised

Female Reproductive Health

An unspayed female usually comes into heat about twice a year, with a swollen vulva and a bloody discharge.31,32 A discharge that is pus-like, bad-smelling, or appears when she isn't in heat isn't normal.11,27 Many unspayed females show some signs of false pregnancy after a heat, which usually pass on their own.28 See swollen vulva in dogs, dog pregnancy and spaying.

Male Reproductive Health

A dog's penis briefly showing when he's excited is normal. A penis that stays out is not.13,3 Both testicles should be in the scrotum by 2 to 4 months of age, and retained testicles carry a much higher cancer risk.14 Older unneutered males commonly develop an enlarged prostate, which can cause blood in the urine or from the penis.3,19 See dog penis problems and neutering.

Spay and Neuter Decisions

Spaying prevents pyometra and heat cycles, and spaying before the first heat sharply lowers the risk of mammary cancer.21,15 Neutering prevents testicular tumors and reduces prostate enlargement and some behaviors such as roaming.33,3 Both raise the risk of weight gain, and in some large breeds early surgery is linked to more joint disorders and certain cancers.20,34 Vets now tailor the timing to the dog's size, breed and lifestyle.6,5

Frequently Asked Questions

What is the most serious reproductive problem in female dogs?

Pyometra, a uterine infection in unspayed females that needs emergency treatment.

Is discharge from my dog's vulva normal?

A bloody discharge during heat is normal. Pus, a bad smell, or discharge in a spayed dog needs a vet.

Why does my male dog have blood in his urine?

In older unneutered males, an enlarged prostate is a very common cause, but urinary infections, stones and tumors are also possible. See your vet.

What age should I spay or neuter my dog?

It depends on size and breed. Ask your vet to weigh the pros and cons for your dog.

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Sources and further reading

This article was written and fact-checked on October 22, 2026 against current veterinary references and specialist guidelines:

  1. Memon MA. Reproductive Disorders of Female Dogs. Merck Veterinary Manual (pet owner version), reviewed June 2018, updated September 2024.
  2. Barnes C, Weir M, Ward E. Pyometra in Dogs. VCA Animal Hospitals, updated May 2026.
  3. Davidson AP. Reproductive Disorders of Male Dogs. Merck Veterinary Manual (pet owner version), reviewed June 2018, updated September 2024.
  4. Grannum S. Testicular Tumors in Dogs. PetMD, May 2023.
  5. American Veterinary Medical Association. Elective spaying and neutering of pets. AVMA, undated.
  6. American Animal Hospital Association. Spay and neuter timing. 2019 AAHA Canine Life Stage Guidelines. AAHA, October 2019.
  7. Morrison BJ. Paraphimosis in Dogs. PetMD, November 2023.
  8. Scully CM. Dystocia in Small Animals. Merck Veterinary Manual, reviewed July 2023, updated July 2026.
  9. Koziol JH. Your Dog is Expecting (VA-29-W). Purdue University Extension, January 2021.
  10. Weir M, Williams K, Llera R, Ward E. Eclampsia in Dogs. VCA Animal Hospitals, updated June 2025.
  11. Eldredge DM. Why Is My Dog's Vulva Swollen? Whole Dog Journal, January 2025.
  12. Davidson AP. Balanoposthitis in Dogs and Cats. Merck Veterinary Manual, reviewed April 2025, updated June 2025.
  13. PetMD Editorial; reviewed by Kleszynski B. A Dog's Penis: Everything You Need To Know. PetMD, updated November 2023.
  14. Weir M, Williams K, Llera R, Downing R, Ward E. Retained Testicle (Cryptorchidism) in Dogs. VCA Animal Hospitals, updated May 2025.
  15. Cornell University College of Veterinary Medicine. Mammary Cancer. Riney Canine Health Center, undated.
  16. Jitpean S, Hagman R, Ström Holst B, et al. Breed variations in the occurrence of pyometra and mammary tumours in Swedish dogs. ISCFR/EVSSAR Symposium (IVIS), July 2012.
  17. Jitpean S, Ström-Holst B, Emanuelson U, et al. Outcome of pyometra in female dogs and predictors of peritonitis and prolonged postoperative hospitalization in surgically treated cases. BMC Veterinary Research 2014;10:6.
  18. Hagman R. Canine Pyometra: What Is New? ISCFR/EVSSAR Symposium (IVIS), July 2016.
  19. Boulding S. Canine benign prostatic hyperplasia. Vet Times, September 2023.
  20. British Veterinary Association, British Small Animal Veterinary Association. BVA and BSAVA policy position on neutering of cats and dogs. BVA, December 2025.
  21. American College of Veterinary Surgeons. Spay. ACVS, updated June 2023.
  22. Varney D, O'Neill D, O'Neill M, et al. Epidemiology of mammary tumours in bitches under veterinary care in the UK in 2016. Veterinary Record, 2023;e3054.
  23. Scully CM. Cystic Endometrial Hyperplasia-Pyometra Complex in Small Animals. Merck Veterinary Manual, reviewed July 2023, updated July 2026.
  24. Scully CM. Vaginitis in Small Animals. Merck Veterinary Manual, reviewed July 2023, updated July 2026.
  25. Root Kustritz MV. Vaginitis in dogs: A simple approach to a complex condition. dvm360, October 2008 (reviewed April 2019).
  26. Scully CM. Vaginal Hyperplasia in Small Animals. Merck Veterinary Manual, reviewed July 2023, updated August 2026.
  27. Coates J. Dog Vagina Health Guide: Everything You Need to Know. PetMD, updated April 2024.
  28. Barnes C, Weir M, Ward E. False Pregnancy or Pseudopregnancy in Dogs. VCA Animal Hospitals, updated April 2024.
  29. Weir M, Barnette C. Mastitis in Dogs. VCA Animal Hospitals, updated July 2025.
  30. Davidson AP. Paraphimosis in Dogs and Cats. Merck Veterinary Manual, reviewed April 2025, updated May 2025.
  31. Weir M, Llera R, Yuill C. Estrous Cycles in Dogs. VCA Animal Hospitals, updated June 2025.
  32. Johnstone G. Everything You Need to Know About Dogs in Heat. American Kennel Club, updated August 2026.
  33. Canadian Veterinary Medical Association. Neutering of Male Dogs. CVMA, October 2012.
  34. Hart BL, Hart LA, Thigpen AP, Willits NH. Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. Frontiers in Veterinary Science 2020;7:388.

About this article

Last updated : new page, written using the Merck Veterinary Manual, VCA, AAHA, the AVMA, the American College of Veterinary Surgeons, Cornell, UK veterinary associations and Swedish and UK research on pyometra.

This page is for general information and is not a substitute for an exam by your veterinarian.