The general popular consensus is that all pets should be surgically altered as soon as possible. Being a proponent for anything else seems to be like taping a big target to your back. But the veterinary community is growing and learning and I personally would really like every puppy family I work with to consider delaying any spay or neuter procedure until after your dog has reached maturity. 

Let's tackle this like a Q&A...

What's a spay?

Removing the ovaries in a female animal. 

What's a neuter?

Removing the testicles in a male animal. 

Why are these procedures so popular?

Most pet animals in the US don't come from responsible breeders or responsible families. Most come from situations where a bitch is impregnated either through irresponsibility, lack of intervention, failure to contain her, or otherwise indifference on behalf of her owner. Shelters and rescues across the country are full of unwanted, unintended animals. It is the shelter's prerogative to encourage altering all dogs and to do so as early as possible to prevent overpopulation. 

No puppy that I have ever produced, and likewise no puppy ever produced by the many breeders I work with and respect, has ever or will ever end up in a shelter. Breeders like myself always take our puppies back when needed, no matter the situation, and find them a new home. It's a part of our job. Shelters are full of dogs from breeders and owners with no accountability or no other options.

Let me emphasize, the overpopulation problem is NOT a result of careful, educated, responsible breeders who devote their life to the preservation of a purebred breed and all of it's intended implications. 

When little or no thought went into breeding and birthing, similarly little or no thought goes into rearing or raising the litter. As such, behavior problems are rampant in puppies resulting from poor breeding, backyard breeding, puppy mills, etc.

Why should someone have their dog spayed or neutered early (before maturity)?

Various clinical studies have shown a significant reduction in the rates of mammary cancer as well as ovary cancer in spayed females. Likewise, testicular and prostate cancer is reduced in neutered males. 

Some behavioral issues can be reduced such as: a female wondering during a heat cycle in search of a male, a male wondering to find a female he smells in heat, males lifting their legs to mark is sometimes reduced in neutered males, humping or other advances towards other dogs and humans is often reduced. Aggression can sometimes be reduced, however, sterilization is not a reliable solution to aggression. 

If you cannot contain your male dog not to breed intact females or your female during heat not to be bred unintentionally than you should seriously consider a sterilization option. The hard truth is that shelters are full of unwanted pets, millions of which are euthanized each year. If you cannot prevent unwanted pets, have your pets fixed. It's that simple. 

What's the alternative? 

Containment is the best cure. I own, at the time of writing this article, 7 intact females and 2 intact males. No one ever breeds if I don't plan them too. Everyone is watched every day for signs of heat and separated to prevent unwanted puppies. Crates, kennels, fences, even the house all serve to separate my dogs from each other if I want to prevent puppies. Likewise, my dogs never leave my property without me! Certainly no female I own goes wondering to interlude with the various loose ranch dogs in the area. 

I've heard it said that sterilizing your pet is the lazy option. How true? If he or she cannot reproduce, than you're off the hook! Containment takes a little more observation and care on behalf of the human. 

Why should someone NOT spay or neuter their pet early? 

Grab your coffee, folks. 

The reproductive system is a large part of the endocrine system. It helps to produce and regulate the flow of hormones designed to aid in immune health, growth, digestion, brain function, muscle production and about 1000 other bodily functions. Think about humans: we can take synthetic hormones pertaining to insulin production, thyroid function, serotonin inhibition -- the list goes on and on. If someone removed a large portion of our endocrine system we'd really be struggling, too.

Dogs are generally very stoic so it's difficult for us to detect whether or not a spay or neuter, probably performed in early puppyhood, has any impact on their day to day life. Rather, we should look to the changes we can document.

A 2002 study at the University of Purdue of 683 Rottweilers – a breed known to be at high risk of bone sarcoma – concluded that the risk for bone sarcoma was significantly influenced by the dogs’ ages at sterilization. According to the study, “Exposure to endogenous sex hormones appears to be protective, as suggested by the high risk for bone sarcoma in male and female dogs that undergo gonadectomy within the first year of life.”

The Purdue study quoted data from a 1998 study (Ru G., Terracini B., Glickman L. T.: Host related risk factors for canine osteosarcoma) that found neutered dogs were at 2.2 times greater risk of osteosarcoma than sexually intact dogs.
— C.C. Holland, Whole Dog Journal

Growth and the resulting side effects is probably the main concern of early spay and neuter; that is altering your pet before he or she has reached full maturity. Their growth is significantly changed. Growth plates aren't provided proper hormone amounts to fuse correctly. Muscle tone is significantly diminished as a result of a lack of testosterone in both males and females. As a result of these two side effects bones grow longer and thinner and muscle tone is reduced so the weight of the dog is supported by joints which are stressed from the excess workload. Often, a dog who experienced an early spay or neuter looks taller, gawkier than one who did not -- noted often in littermates. 

In 2013, the UC Davis School of Veterinary Medicine published a study revealing that neutered golden retrievers are seemingly at a higher risk of joint disorders and cancers compared to sexually intact dogs of the same breed.
— American Animal Hospital Association

When should I spay or neuter my pet?

After maturity, or about 3 years for most large breeds. At this point their joints are fused and their muscle mass has developed properly thanks to the presence of adequate hormone levels. Most of the research quoted above and in the links below pertains to sterilization before 6 months of age. Adverse long term health reactions are amplified by altering your pet very young. Less research is available on altering your pet after maturity. 

It is your responsibility to prevent unintended litters until the time you do have your pet altered. Males can breed a female at any time. Females have seasons or "heat" cycles evident by blood show from the vulva. A heat cycle lasts up to a month, even if the bleeding is no longer evident. She should be contained away from male dogs for the entire duration of her heat cycle.  

What about new procedures such as ovary sparing or vasectomy? 

Ovary sparing, or removing the uterus and leaving the ovaries, is my recommended procedure for all female puppies purchased from me. Ideally, this procedure should be performed after puppyhood and is a reliable way to prevent puppies without reducing hormone production as much as a traditional ovary removal. 

Vasectomy, or severing both the tubes that transport sperm but leaving the testicles, is my recommended procedure for all male puppies purchased from me. Once again, ideally this procedure should be performed after puppyhood and is a reliable way to prevent unintended puppies. 

What if I don't want to spay or neuter my pet at all, including alternative surgeries?

Prevent unwanted puppies. Build fences, crate your pets when you cannot supervise, and supervise. 

In Rottweilers especially, the prevalence of bone cancer in surgically altered pets is high enough to consider not altering your Rottweiler. Ovary cancer is not high enough in Rottweilers to use it as the core reason to perform a spay. Mammary cancer is high enough in Rottweilers to consider it as a reason to spay your female, as is the occurrence of pyometra. 

Having your pet spayed or neutered is only one of many factors that contribute to the increase or decrease in cancer rates; as such avoiding or performing these procedures along won't prevent cancer. Other influences such as genetic predisposition, over vaccination, and diet should be researched. 

We have chosen not to surgically alter any of our Rottweilers, even those we do not plan to breed or who we have retired from breeding. In the situation that we did choose to surgically alter one of our Rottweilers we would use alternative surgery options such as ovary sparing or vasectomy. 

Recommended Reading

Health Implications in Early Spay and Neuter in Dogs

Spaying and Neutering - The Risks and Benefits

UC Davis Study Compare Long Term Health Effects of Neutering...

Parsemus Foundation - A very valuable tool including definitions of alternatives to traditional spay/neuter procedures, help finding veterinarians who offer alternative procedures, and much more!