News

By Pat Bailey

Neutering, and the age at which a dog is neutered, may affect the animal’s risk for developing certain cancers and joint diseases, according to a new study of golden retrievers by a team of researchers at the University of California, Davis.

The study, which examined the health records of 759 golden retrievers, found a surprising doubling of hip dysplasia among male dogs neutered before one year of age. This and other results were published Feb. 13 in the online scientific journal PLOS ONE.

“The study results indicate that dog owners and service-dog trainers should carefully consider when to have their male or female dogs neutered,” said lead investigator Benjamin Hart, a distinguished professor emeritus in the UC Davis School of Veterinary Medicine.

“It is important to remember, however, that because different dog breeds have different vulnerabilities to various diseases, the effects of early and late neutering also may vary from breed to breed,” he said.

While results of the new study are revealing, Hart said the relationship between neutering and disease-risk remains a complex issue. For example, the increased incidence of joint diseases among early-neutered dogs is likely a combination of the effect of neutering on the young dog’s growth plates as well as the increase in weight on the joints that is commonly seen in neutered dogs.

Dog owners in the United States are overwhelmingly choosing to neuter their dogs, in large part to prevent pet overpopulation or avoid unwanted behaviors. In the U.S., surgical neutering — known as spaying in females — is usually done when the dog is less than one year old.

In Europe, however, neutering is generally avoided by owners and trainers and not promoted by animal health authorities, Hart said.

During the past decade, some studies have indicated that neutering can have several adverse health effects for certain dog breeds. Those studies examined individual diseases using data drawn from one breed or pooled from several breeds.

Against that backdrop, Hart and colleagues launched their study, using a single hospital database. The study was designed to examine the effects of neutering on the risks of several diseases in the same breed, distinguishing between males and females and between early or late neutering and non-neutering. 

The researchers chose to focus on the golden retriever because it is one of the most popular breeds in the U.S. and Europe and is vulnerable to various cancers and joint disorders. The breed also is favored for work as a service dog.

The research team reviewed the records of female and male golden retrievers, ranging in age from 1 to 8 years, that had been examined at UC Davis’ William R. Pritchard Veterinary Medical Teaching Hospital for two joint disorders and three cancers: hip dysplasia, cranial cruciate ligament tear, lymphosarcoma, hemangiosarcoma and mast cell tumor. The dogs were classified as intact (not neutered), neutered early (before 12 months age), or neutered late (at or after 12 months age).

Joint disorders and cancers are of particular interest because neutering removes the male dog’s testes and the female’s ovaries, interrupting production of certain hormones that play key roles in important body processes such as closure of bone growth plates, and regulation of the estrous cycle in female dogs.

The study revealed that, for all five diseases analyzed, the disease rates were significantly higher in both males and females that were neutered either early or late compared with intact (non-neutered) dogs.

Specifically, early neutering was associated with an increase in the occurrence of hip dysplasia, cranial cruciate ligament tear and lymphosarcoma in males and of cranial cruciate ligament tear in females. Late neutering was associated with the subsequent occurrence of mast cell tumors and hemangiosarcoma in females.

In most areas, the findings of this study were consistent with earlier studies, suggesting similar increases in disease risks. The new study, however, was the first to specifically report an increased risk of late neutering for mast cell tumors and hemangiosarcoma.

Furthermore, the new study showed a surprising 100 percent increase, or doubling, of the incidence of hip dysplasia among early-neutered males. Earlier studies had reported a 17 percent increase among all neutered dogs compared to all non-neutered dogs, indicating the importance of the new study in making gender and age-of-neutering comparisons.

Other researchers on this UC Davis study were: Gretel Torres de la Riva, Thomas Farver and Lynette Hart, School of Veterinary Medicine; Anita Oberbauer, Department of Animal Science; Locksley Messam, Department of Public Health Sciences; and Neil Willits, Department of Statistics.

Media Resources

Pat Bailey, Research news (emphasis: agricultural and nutritional sciences, and veterinary medicine), 530-219-9640, pjbailey@ucdavis.edu

Benjamin Hart, School of Veterinary Medicine, 530-219-3298, blhart@ucdavis.edu

By Carol Beauchat

Many studies have documented that genetics explains part of the variation among dogs in hip scores. This is usually 15-30% of the total variation, but in some cases it can be as much as 60%.

This means that environmental factors must account for the remainder of the variation; i.e., as little as 40%, but usually 70-85%.

When breeders are focusing on selection to improve hips, they are trying to chip away at genetics, which usually matters much less than environmental factors.

“Environment” as used here encompasses all factors that are “not genetic”, which can be anything from type of exercise to food consumption.

One way to tease out the effects of these environmental factors is to isolate one, manipulate it, and observe the effect on the trait of interest, in this case, the hip score. There are hardly any studies of this sort on hip dysplasia dogs, but there is one on rats that is key to understanding the role of traction in the whelping box in the risk of developing hip dysplasia.

I have explained to you the importance of a tiny ligament (teres ligament) in the hip socket that keeps the head of the femur snugly in the hip socket in newborn puppies. ([Do your puppies have enough traction in the whelping box?](https://www.instituteofcaninebiology.org/…/do-your…)) In that post, I showed you how that ligament is stressed when the puppy’s legs are in the “extended and adducted” position (straight behind the puppy and pulled together). (Review that explanation if you don’t remember how this works – it’s important). This position of the legs can result in hip dysplasia in human infants, as when the baby is swaddled up tightly like a burrito. How can we prove that the same mechanism applies in animals besides humans?

You could do an experiment with animals that mimics the “burrito swaddle” by putting the legs in the extended/adducted position and looking at the effect on hip conformation.

Here’s a study that did exactly that. This experiment was on rats, but similar studies have been done with rabbits and other mammals. The experiment was simple. The legs of baby rats were taped together (“swaddled”) and evaluated after 5 days and 10 days, and compared to a control group (no tape).

The prevalence of developmental dysplasia was highest in the pups that were swaddled for the entire 10 days (36 of 44 pups), and in most of these the hips were dislocated. Dysplasia (as subluxation) was less frequent (21 of 44) in the pups swaddled for only the first 5 days or the second 5 days.

Think about this. These rat pups differed only in whether their legs were taped together or not. So it is the position of the legs – extended and adducted – that resulted in hip dysplasia. In the pups with legs taped for 10 days, the teres ligament was simply gone. In pups with legs taped for only 5 days, the teres ligament was present but damaged.

The first question you are asking is whether we know if this applies to dogs. A similar experiment has been done on puppies, but one leg was put in a cast to keep it in the extended position, and this also resulted in dysplasia in the hip on that side.

How is this relevant to dogs? Look at the many photos and videos of very young puppies nursing and crawling around in whelping boxes with poor traction. The back legs are extended and adducted, over and over, as the pup tries to push itself forward. Over the course of the three to four weeks before it starts to walk, a puppy could do this thousands of times, putting stress on the teres ligament every time.

From the experiment on rats and others that have been done on other newborn mammals, we should expect this leg movement that we usually call “crawling” will result in dysplastic hips.

Notice that although all of the rat pups in a treatment group were treated the same way, not all of them developed hip dysplasia (e.g. 36 of 44 in the 10 day group). The reason for this would have to be revealed in additional studies, but it demonstrates that we should not expect clear, consistent differences among the animals in each group.

The purpose of the Traction Mat is specifically prevent this leg position of extended and adducted. It does not provide general traction like a rough surface would, but instead provides a vertical surface the pup can push against instead of slipping over the surface of the floor.

If you understand this, you will realize that we will never solve the hip dysplasia problem by trying to choose parents with better hips and removing the others from the breeding stock. This also means, however, that if the teres ligament is damaged early in a pup’s life, other factors – both environmental, like exercise and overweight, and genetic, like large body size – can determine the whether dysplasia is modest or severe.

If you want to produce dogs with sound hips, you must protect the teres ligament from the damage that occurs when the puppy extends and adducts the back legs to try to move itself forward.

In fact, we cannot eliminate hip dysplasia in dogs without doing this, because the risk starts at the moment of birth, and the damage is done in the first few weeks after whelping. We know from the rat study that we can’t expect every puppy, even in the same litter, to have excellent hips. But we should be able to reduce the incidence and severity of hip dysplasia by addressing the basic traction problem.

————————–

REFRENCES

Does Swaddling Influence Developmental Dysplasia of the Hip? (the rat study)

http://bit.ly/Wang_rats

A Dynamic Canine Model of Experimental Hip Dysplasia (the dog study)

http://bit.ly/Schoeneker

_____________________________

Learn more here –

ICB Hip Dysplasia Project

https://www.facebook.com/groups/ICBHipDysplasiaProject