Sees limitations to longevity study of Rottweilers

It is unfortunate that the recent JAVMA News article¹ reporting on research involving Rottweilers and longevity did not put the study into broader perspective. There is minimal acknowledgement of the study's limitations, and no attempt is made to balance the findings with the substantial body of scientific research demonstrating the positive health benefits of ovariohysterectomy in dogs.

The study does not prove convincingly that retaining ovaries was the cause of the dogs' longevity. One of the most important shortcomings was that the study used groups that were preselected to have certain outcomes. For example, the group that lived to an exceptional age obviously had fewer cancer-related deaths than did the usual-age group. A study design that used the entire database, randomly selected and categorized dogs on the basis of time of gonadectomy, and then examined longevity would potentially have yielded more accurate results.

Second, the authors completely ignored the population of dogs that remained sexually intact. If their premise is true, then sexually intact dogs should have been the longest lived, which may not be supportable. The study design should have included a group of sexually intact animals.

Third, the authors failed to fully discuss the fact that there was an “apparent familial clustering of exceptional longevity.”² This has been found to be the case in humans, too. Genetics, rather than ovary retention, may be the key to exceptionally long life in some individuals. The authors do not adequately address the fact that cancer caused a much greater loss of life in the usual-age group than in the exceptional-age group. It would appear that resistance to cancer (a genetic issue) was a strong determinant of longevity and may have been more important than ovary retention.

Fourth, dogs that lived longer certainly had more opportunity to be spayed later in life. Dogs with shorter life spans would have had less time to be spayed than those with longer life spans. This would have skewed study data and could help explain the difference in ovary retention times.

Fifth, this research studied only one canine breed and thus should not be used to make sweeping recommendations for all dogs.

Sixth, the authors selected one factor—ovary retention—while ignoring others of probable importance such as cancer resistance, exceptional-age mothers, diet, exercise, regularity of veterinary care, and housing. Those animals with superior reproductive potential may have been cared for more attentively than those without that potential, perhaps influencing outcomes and delaying ovariohysterectomy.

Seventh, because this was a short communication and the authors acknowledged that statistical analyses were incomplete, evaluation is more difficult.

Although longevity is of great interest in both human and veterinary medical research, the Rottweiler study is not definitive. Providing high-quality lifetime companion animal care, along with a consideration of pet overpopulation dynamics, should remain our focus as veterinarians. We must ensure that our clients are properly educated regarding the substantial health and welfare benefits provided by gonadectomy and counsel them accordingly.

Paula Kislak, dvm

Santa Barbara, Calif

More on accidental overdosage of joint supplements

We would like to respond to the recent letter¹ concerning accidental ingestion of overdosages of joint supplements in dogs. Veterinarians may not be aware of the National Animal Supplement Council (NASC). This nonprofit organization represents over 100 companies that provide supplements for companion animals (dogs, horses, and cats). Established in 2002, the NASC works cooperatively with state and federal regulatory agencies to ensure quality and manage risk for both products and individual ingredients. The NASC Adverse Event Reporting System (NAERS), created in 2003 and accessible by the FDA, Center for Veterinary Medicine, tracks adverse events that are defined as “…a complaint involving an animal health or nutritional supplement linked to any negative physical effect or health problem that may be connected to or associated with use of the product.”² An adverse event does not necessarily imply causation (ie, the event was due to use of the product); the adverse event may have occurred in an animal with an underlying medical condition or receiving concurrent medication with potential adverse effects during the same time period a supplement was administered. The NASC member companies are required to report all adverse events to the NAERS monthly, in addition to total amount of each product sold by the company.

The two most common ingredients found in joint supplements sold by NASC members are glucosamine and dimethyl sulfone (methylsulfonylmethane). The number of doses of supplements containing glucosamine sold for use in dogs during 2008 and 2009, the time period addressed in the recent letter,¹ was > 407 million; the comparable number for products containing dimethyl sulfone was > 340 million. Accidental ingestion is specifically recorded in the NAERS when NASC members enter their monthly adverse event reports. Analysis of NAERS data reveals that during 2008 and 2009, < 1 accidental ingestion in dogs was reported for every 1 million administrations of supplements containing glucosamine or dimethyl sulfone sold.

The NASC continuously monitors > 4,200 products with > 1,400 ingredients through the NAERS. The total number of administrations for all products sold in the NAERS database is now over 38 billion. The incidence of reported adverse events from collective NAERS data is 0.08/1 million administrations of all products sold for companion animals. The commitment of NASC members to product quality, combined with risk assessment data available through NAERS and accessible by the FDA, Center for Veterinary Medicine, provides veterinarians with a level of confidence that companion animal supplements are indeed safe. More information on the quality system standards required of NASC member companies may be found at www.nasc.cc.

Theresa A. Brim, dvm, phd

Valley Center, Calif

Susan G. Wynn, dvm

Sandy Springs, Ga

Lydia F. Gray, dvm, ma

Plymouth, Mass

L. Phillips Brown, dvm

Boise, Idaho

Responsibilities of veterinarians on issues of antimicrobial resistance

Mounting evidence regarding the development of bacterial resistance to antimicrobials provides us as veterinarians with important roles regarding our professional services to animal agriculture.¹ The current practice within the US food animal production industry of administering low concentrations of antimicrobials in feed to promote growth and feed efficiency is viewed by industry as a revenue-enhancing measure, despite the costs associated with this practice.²

Yet, it is increasingly apparent from current research that this practice encourages resistance to emerge in the organisms against which the antimicrobials are aimed. Such resistance has been shown to develop rapidly and through a variety of mechanisms with two overarching results: a decline in the effectiveness of antimicrobials and distribution of resistant organisms into food products and the environment.³ Compounding this concern, it has been shown that resistance can be shared among organisms, so that a relatively benign microbe can develop resistance that it may then pass to a more pathogenic one, rendering the latter more resistant to treatment. Further, even if the antimicrobial used in the industrial setting is not identical to the one used by veterinarians or physicians, it has been demonstrated that antimicrobials within the same class as the ones used by industry can have their efficacy threatened.

As veterinarians, we should be concerned that overuse of antimicrobials by industry can threaten the efficacy of the pharmaceuticals we depend on for our patients. And as guardians of public health, we should also be concerned that such overuse can create resistant organisms that might threaten our patients as well as the human community.⁴ As practitioners, we've long recognized that antimicrobial dosages must be sufficiently robust if we are to discourage replication of those organisms that harbor innate resistance. Yet, low dosage applications have become widespread in industry.

Bans on the wholesale use of antimicrobials in feed in parts of Europe, such as the Scandinavian countries, have sometimes been cited as harming the animal production industry. Continued monitoring of the Nordic experience has shown the opposite, however; animal production has increased in the wake of reduced antimicrobial use.^5,6 This was accomplished by implementing best-practice husbandry protocols, such as reducing animal crowding and emphasizing sanitation in the production environment, in combination with therapeutic use of antimicrobials as needed by veterinarians. This precautionary action in the Scandinavian countries has had several positive effects from a veterinary perspective: antimicrobial efficacy has been protected by discontinuing overuse at low dosages, introduction into the environment of resistant organisms that could threaten animal and human health has been curtailed, and animal welfare has been served by improving living conditions for production animals.

Commensurate with our oath and societal obligations, such gains should be viewed as desirable by veterinarians, and our profession accordingly has an interest and responsibility in counseling industry toward strategies that reduce its dependence on widespread use of antimicrobials in feed. Antimicrobials in animal production should be conserved as highly valued veterinary medicines for therapeutic use and available only through veterinary prescription.

Raymond J. Tarpley, dvm, phd

College Station, Tex

Danielle Buttke, dvm, phd

Ithaca, NY