The case for spaying/neutering kittens at 6 weeks, 1.5 pounds

August 2, 2016

In this guest post, Dr. Mehnaz (Chumkee) Aziz looks at the evidence – or lack thereof – for common beliefs about the right age and weight to spay or neuter a kitten.

From preventing unintended litters to helping reduce the chance of pet relinquishment, spay/neuter prior to adoption is recognized as a critical component in eliminating the unnecessary euthanasia of dogs and cats across our communities. Although the scientific debate regarding the optimal age for spay/neuter continues for privately owned animals, in animal sheltering we have recognized and embraced the population, welfare, and societal benefits of early-age spay/neuter.

The direct, individual animal benefits of early-age spay/neuter are also noteworthy. Minimal bleeding and shorter surgery and anesthesia times result in lower perioperative complication rates and rapid recovery. While the conventional minimum age/weight requirement for early-age spay/neuter has been considered to be 8 weeks/2 pounds, more and more shelters are shifting to safely sterilizing pediatrics at 6 weeks or a robust 1.5 pounds.

Based on this trending shift, I decided to look into the origin of the 8 weeks/2 pounds’ minimum age/weight requirement to see if there was a definitive reason 8 weeks was initially chosen. Was it based on anesthestic drug metabolism, surgical considerations, the behavioral developmental phases for pediatrics, or other factors altogether? Interestingly, investigation into the origin of this convention did not yield any discrete evidence-based reasons.

What I did find were a number of scientific studies that relayed practical and safe anesthetic and surgical protocols for early-age spay/neuter starting at 6 weeks of age. That seemed to rule out that anesthetic or surgical considerations were the basis of the convention. So I turned to looking into possible reasons based on the different behavioral developmental phases of pediatrics. I quickly discovered that more research has been done on the development of puppies than kittens. Concerned that perhaps we’ve inappropriately applied what we learned about the development of puppies to that of kittens in terms of the spay/neuter minimum age/weight requirement, I looked for and discovered specific research on differences between puppy and kitten development.

Most of the research focused on the socialization period of behavioral development. The socialization period is the process by which animals develop appropriate social behavior. Early handling and exposure to humans, other animals, and novel stimuli facilitates behavioral and emotional development. Although social behaviors continue to form and develop after this distinct period, the process is much slower and more difficult as fears begin to emerge.

The most significant difference between the developmental phases of dogs and cats is that the cat’s socialization period starts and ends sooner than the dog’s period. For kittens the period is 2 to 7 weeks of age, whereas for puppies it is 4 to 16 weeks. Animals appropriately handled and exposed to a wide range of stimuli during this window are less fearful and are more affectionate and playful with people. Because we know that socialization is one of the key components in defining an animal’s behavior as an adult AND because it is the sensitive period for creating bonds with people, appropriate and adequate socialization during this short window of time is critical in building the foundation of a strong human-animal bond. Research on pet adoption and relinquishment have shown us that a mismatch between owners’ expectations and the actual behavior of cats is a significant risk factor for relinquishment. In the same vein, friendliness in cats is a highly desired trait by pet owners and is an important factor for pet selection in shelters.

That being said, it’s of importance to note that our behavioral expectations for what constitutes a well-rounded dog can be very different from what most of us are willing to accept from our cats. For instance, when pet owners completed surveys about to gauge the seriousness of their pets’ behavior problems, cat owners did not rank animal-to-animal aggression as high of a concern as dog owners did. In the same study, however, both dog and cat owners ranked aggression towards people as being very serious. So, while aggression towards humans is a consistent concern for dog and cat owners, cat owners are seemingly less concerned about their cat getting along with dogs or other cats in the household. Recognizing this difference in owner expectations for dogs versus cats, along with the disparity in socialization periods for dogs versus cats, brings to light the need to reconsider our socialization strategy in shelters in terms of when we spay/neuter. Shifting to a 6 weeks/1.5 pounds as the minimum age/weight requirement makes more sense, particularly for kittens. Since more kittens than puppies go through our shelters nowadays, it seems prudent to reconsider our convention.

To ensure that we adopt out kittens who will grow into friendly, socialized adult cats and have less of a chance of being relinquished, we have to provide kittens with as wide of a range of social and environmental experiences as possible during their critical socialization period. This includes introducing them to as many people, animals, and things that they will likely be living with for the rest of their lives. It also means we should carry, handle, and play with kittens in our care. The challenge for us though is that these animals are at their peak of vulnerability to infectious diseases during their stay with us. In light of this, we know that pediatrics must be moved through the shelter in minimal time. For both puppies and kittens, length of stay in the shelter should be the shortest of all animals.

With this trade-off in mind, moving kittens through our shelters at 6 weeks instead of 8 weeks definitely makes more sense. By getting them into a home before their socialization period ends, we reduce their chance of exposure to infectious diseases AND we send off to their forever home for exposure to all kinds of weird human objects (vacuums, radios, brooms, even cucumbers) and the other animals they are going to live with.

Although providing adequate time with queens and littermates is important for developing some appropriate social behaviors, often we do not have that luxury since we do not always receive queens with litters in shelters. Sending them to a home with another cat (who was hopefully appropriately socialized) can serve as a surrogate instead. In addition, as noted earlier, although socialization with other kittens is important in behavioral growth, cat owners are less concerned with how friendly their cats are with each other. While the socialization period is important for teaching kittens about bite inhibition and impulse control, this is less of a serious concern for cat owners than dog owners later in life. For better or worse, we don’t have to deal with walking our cats down busy, urban streets where we have to eye the cat owner down the sidewalk and nervously anticipate what their cat will do when approaching our cat.

For puppies, whose socialization period extends until 14 weeks of age, the trade-off between holding them in the shelter and adopting them out at a young age still holds true but is more complicated because we want our dogs to be well-socialized with other dogs. By separating them from their littermates and adopting them out at 6 weeks of age (or 8 weeks of age, which we are already doing), we may preclude them from adequate socialization with other puppies. However, with puppy socialization classes becoming more and more ubiquitous, this concern has been mitigated. This, along with the concern for infectious disease exposure in the shelter, makes adopting puppies out sooner than later the better option unless the puppies remain in a very high quality foster home in the meantime.

So all of that research and what did I find? I found that there are no discrete studies or evidence to support a minimum age/weight requirement for spay/neuter. For kittens the minimum age requirement of 8 weeks/2 pounds appears particularly unsubstantiated. Practicing earlier-age spay/neuter is not only safe but it allows shelters to move kittens out of shelters faster, thereby protecting them from infectious diseases. Of equal importance, it helps create well-rounded cats. And who doesn’t love a well-rounded cat??

Just as for any other medical and surgical procedures, veterinarians should make the final call, using their best medical judgment to decide whether an animal is a good candidate for spay/neuter at 6 weeks/1.5 pounds. It’s also important to recognize whether your state has mandates regarding the minimum age requirement for adopting out animals.
So this kitten season – try out a new pilot program and starting spaying/neutering kittens at 6 weeks/1.5 pounds. Get kittens out of the shelter faster, turn foster homes over more quickly, and give them their best chance at building a strong human-animal bond!

dr. mehnaz chumkee azizDr. Aziz is a shelter veterinarian currently completing her residency with the UC Davis Koret Shelter Medicine Program. She went to Tufts Cummings School of Veterinary Medicine to obtain her DVM degree where she participated in multiple international dog welfare and population control projects in Nepal and Bhutan.  She then completed her internship at the ASPCA’s Bergh Memorial Animal Hospital in NYC in 2013, which included experience in anti-cruelty work and shelter medicine.


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