The Power Of Ovaries

While reading this month's (Jan 2010) DVM newsmagazine, I came across the intriguing article, "Retaining ovaries may be a key to prolonged life in women and dogs." It cites a study published in the December issue of _Aging Cell_ that found that "taking away the ovaries during the first four years of life completely erased female survival advantage. We found that female Rottweilers that kept their ovaries for at least six years were four times more likely to reach exceptional longevity compared to females who had the shortest lifetime ovary exposure." The study involved roughly 300 Rotties. It also references a study done at the John Wayne Cancer Institute in Santa Monica, CA earlier this year on women. This study found that while women with ovariohysterectomies before age 50 had a lower incidence of ovarian, uterine and breast cancer, they had increased mortality from other causes compared to women who did not have their ovaries removed before age 50.

I went online to see what else I could find. Physorg.com had an article very similar to the one in DVM newsmagazine if you want to read it for yourself. Here's a quotation from the Rottwieler study's author on his thoughts on why removing the ovaries in early life in dogs causes problems:

What we have here is a compelling convergence. The data from women and dogs, together with reported longevity benefits from ovary transplants in mice, are pointing in the same direction - the notion that a network of processes regulating longevity is under ovarian control.

I was also able to find three other online articles that summarize two different studies on the effect of removing ovaries before age 50 on women's lifespan. There's an article in ScienceDaily from Sept 15, 2006 citing an October 2006 journal article in Lancet Oncology: "Preventative Ovary Removal Linked to Early Death In Younger Women, Mayo Clinic Discovers." And here is the Mayo Clinic's summary of their research, which indicated an increased risk for dementia as a possible sequela of early ovary removal. Finally, here's an article from the SF Sexual Health Examiner, "Removing the Ovaries Before Menopause Increases a Woman's Risk of Dying From Heart Disease." on an article in the journal _Menopause_ about a Mayo Clinic study.

The Mayo Clinic study published in Lancet Oncology gives several possible reasons that removing ovaries increases the risk of early death. The most plausible one for me was that premature estrogen deficiency following the surgery increased the risk for various diseases that in turn reduced survival. However, the truth is that we don't understand the ovary's role in aging and risk of a death.

I know that human surgeons are now much more hesitant about removing a young woman's ovaries. If these articles weren't convincing enough, _Menopause lifestyle_ gives five succint reasons to hang onto your ovaries in this article.

What I wonder is will this sentiment carry over into veterinary medicine? Will we offer clients the option of leaving a dog's ovaries intact when we spay? Given that being spayed after even one heat cycle is a known risk factor for breast cancer in dogs, it seems like this would be controversial even from a medical standpoint. From a behavioral perspective, it would also be controversial since it would not eliminate heat cycles and so the dog would attract male dogs when in heat along with their associated behavior and attempts to mate with her. However, I learned in my behavior class that spaying a female dog increases the likelihood of her becoming aggressive because of the absence of progesterone post-spay so that would be one potential advantage of leaving the ovaries intact.

I suspect veterinary medicine will be slow to change and that we will be performing ovariohysterectomies and not just hysterectomies on dogs for a long time to come. I do find this research intriguing and am very curious to see more research elucidating the mechanisms by which ovaries play a role in longevity.