#isolements

The short answer is, some of the studies are good, and some kind of suck but people quote them anyway. There are risks to spaying and neutering pets, but there are also a lot of benefits. Each species is also different. Risks and benefits for spaying a cat aren’t the same as neutering a dog. And don’t even get me started on exotics. What I have found incredibly interesting during my education is that we have talked A LOT about desexing–in theriogenology (repro medicine), oncology, surgery, and nutrition, and every single one had a different opinion on when/if animals should be desexed. So it’s all about weighing the pros and cons.

**These are statistics based on my theriogenology notes, which come from a boarded theriogenologist and their own research**

Female cats

Pros: Population control. Spaying also reduces the risk of mammary cancer, which is the 3rd most common tumor in cats (incidence 2.5%). The incidence is even more reduced when you spay before the first heat, as each heat cycle increases incidence. In cats, more than 90% of mammary tumors are malignant adenocarcinomas. You’re also reducing the incidence of uterine tumors, ovarian tumors, and pyometra. Cons: Surgical complications. Also, increased incidence of feline lower urinary tract disease (FLUTD), obesity, and diabetes (incidence 0.6% for FLUTD, 0.5% for DM).For me, this is an easy one: you are greatly reducing the risk of a highly malignant cancer, and increasing the risk of manageable conditions. The pros greatly outweigh the cons.

Male cats

Pros: Population control. Normal tom breeding behavior is also quite aggressive, and not super pleasant to live with (biting, spraying). Very simple surgical procedure. Cons: Increased risk of obesity.Another easy one for me. Unwanted cat populations are out of control, and there are absolutely no significant risks that we know of associated with castrating a male cat. Obesity can be controlled with diet and exercise. So there’s no reason not to neuter a male cat. It’s also an incredibly easy and fast surgery. Honestly, it’s barely a surgery.

Female dogs

Pros: Population control. Like cats, the incidence of mammary cancer in dogs increases significantly with every heat. Mammary cancer is the most common tumor of the female dog (incidence 3.4%). It is less malignant than in cats (~51% are malignant), but metastases are found more often than not in those cases, especially in the lungs. You also reduce the incidence of uterine cancer, ovarian cancer, and pyometra (incidence 15% by age 4, 23-24% by age 10). Mortality for pyometras ranges from 0-17%Cons: Complications of surgery. This next part is where a lot of the anti spay/neuter articles get their facts from: there seems to be an increased incidence of transitional cell carcinoma, hemangiosarcoma, lymphoma, osteosarcomas, and cutaneous mast cell tumors. There can be some serious mortality associated with these cancers, and this is a lot of the fuel for the anti-spay crowd. Here’s the thing though: the incidence is still quite low, and some of the studies that reported this were meh. Study sizes that were small, or breed focused, or just not reported well. That being said, those are deadly diseases, and there does seem to be some correlation between spaying and an increased incidence of these cancers that we don’t understand. So while it shouldn’t be brushed off, simplifying it to “spaying causes cancer” isn’t right either. Spaying is also associated with an increased incidence of cranial cruciate ligament (CCL) injuries, hip dysplasia, diabetes mellitus, obesity, urethral sphincter mechanism incompetence (USMI), and possibly reactivity in one breed (I think Springers but I’m not 100% sure). From the nutrition perspective, an animal’s metabolic needs are ~halved when they are spayed/neutered. This is true for both cats and dogs, males and females. There are concerns associated with cutting down the metabolic needs of a growing animal. The reason I’m specifically bringing this up with dogs is because we have dog breeds that grow to over 100, even 150lbs in 1-1.5 years. This is where things get a little muddier. You have an increased (though still low) incidence of deadly diseases if you do spay, but an increased incidence of a common and still sometimes deadly disease if you don’t spay. There are other curable morbidities associated with spaying as well, and certain breeds will be at even higher risk (CCL injuries and hip dysplasia). A lot more recommendations are coming out now to wait until skeletal maturity to spay or neuter a dog. If you are going to keep your female intact, keeping up on regular vet visits is important, as is watching for any lumps/bumps in the mammary chain and treating them as malignant until you can prove otherwise. And of course, understanding the canine reproductive cycle. In one study, 57% of people that owned an intact bitch had no idea that they cycled twice per year, and 56% of litters were unplanned. If your dog is going to remain intact, you need to be prepared to manage her to prevent unwanted litters. You have to be able to prevent intact dogs from getting to her when she’s in heat (and understand what “in heat” looks like). If you can’t do that, spay your dog.

Male dogs

 Pros: Population control. Males are able theoretically able to reproduce with many females every year, whereas females are limited to twice yearly (or once yearly for some breeds), so there is potentially an increased benefit for population control in castrating male dogs. Decreased incidence of testicular neoplasia and benign prostatic hypertrophy (BPH). BPH is extremely common, with an incidence of 75-80% in male dogs over age 6. Castration is considered curative. Mortality is very low for this disease. There have been some reports of increased lifepsan in neutered dogs, but it’s unclear if this is because neutering reduced “risky” behaviors associated with intact males like roaming, or because owners that neuter are often “invested” in their pets.Cons: Complications of surgery.  Once again, we see an increased risk of some pretty nasty cancers. Prostatic neoplasia, transitional cell carcinoma, osteosarcoma, hemagiosarcoma, and lymphoma. Again, those cancers are low incidence, but high mortality. When we have a neutered male dog with prostate disease, it is most likely prostatic neoplasia, whereas with intact male dogs it tends to be more likely BPH or prostatitis. We also see the same increase in CCL injuries and hip dysplasia that we see with females. Also muddier than cats, so you really need to take the individual into consideration. Can you keep your male dog contained? Male dogs have been known to climb fences to get to females in heat. Is this a breed that is already predisposed to CCL injuries or osteosarcoma? It’s worth noting that it is a myth that neutering makes a dog less aggressive. Neutering won’t fundamentally change a dog’s personality. Dog bite statistics tell us that intact male dogs are more likely to bite. This isn’t necessarily because intact dogs are “meaner”. What is more likely happening is that irresponsible owners are more likely to own an intact dog, because they don’t want to bother with neutering them. This does NOT mean that people that own intact dogs are automatically bad owners, but that statistically, bad owners are less likely to neuter their dogs (or provide vet care, or proper containment, etc). Intact dogs are also more likely to roam. It is that combination (lack of responsibility, inc likelihood to roam) that most likely makes intact males appear more often in bite statistics.

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