While it's generally accepted that pets become the equivalent of senior citizens around age 7, various dog breeds reach this milestone at different ages based on their size and weight. Following are the 50 most popular dog breeds in the U.S. (according to American Kennel Club 1998 registrations) and the corresponding ages at which they become senior citizens.

Each dog will age at his/her own pace, but visible signs of aging -- such as changes in appetite or weight, increased thirst or urination, dulling or thinning of fur, and difficulty moving, among others -- become evident within the time-frame noted below for each breed. If left unchecked, conditions related to aging can result in reduced lifespan or unnecessary pain and suffering.

When dogs reach their senior years, owners need to pay extra attention to their pets' diet and lifestyle, and conduct twice-yearly veterinary visits for screenings of potential health problems such as arthritis, heart disease, vision or hearing impairments, Cognitive Dysfunction Syndrome (altered mental functioning) and other aging-related ailments.

For unknown or mixed breeds, owners can follow these guidelines to determine when their dogs become senior citizens based on weight:

To help owners easily identify their dogs' entrée in to senior citizenship, Beaphar Inc. USA developed this chart, which was reviewed for accuracy by Dr. David J. Waters, D.V.M., Ph.D., Associate Professor of Surgery and Comparative Oncology, Purdue University and Dr. E. Gregory MacEwen, D.V.M, Professor of Medical Sciences, University of Wisconsin-Madison School of Veterinary Medicine. Neither Dr. Waters nor Dr. MacEwen are associated with Beaphar B.V. or Beaphar Inc. USA, and their contributions to the information contained in this chart do not constitute an endorsement of Beaphar's products.

Beaphar Inc. USA, a division of Beaphar B.V., Europe's premier manufacturer of pet care products, is leading the way in senior pet education and nutrition. Known throughout Europe for its high-quality ingredients and pet care products, the Senior Line products are specially-formulated to provide the additional vitamins, minerals and nutrients required by the senior citizen canine.

SPAY/USA is a network of volunteers and veterinarians working together to popularize and facilitate spay/neuter services through a nationwide toll-free referral service. Their mission is to end pet overpopulation.

They have over 950 programs and clinics nationwide with about 8,000 top-notch veterinarians in the network as of mid-1999. Their goal is to make affordable spay/neuter services available to those who would not otherwise spay or neuter their pets.

The veterinarians are paid directly by the pet guardian at the time of service; there is a referral slip from SPAY/USA, but no complicated paperwork to fill out. The program consists of veterinarians, willing to reduce their price (if it is not already very affordable) for people bringing in a SPAY/USA certificate. When people call the toll-free number, 1-800-248-SPAY, they are referred to a veterinarian.

The US has over 55,000 practicing veterinarians. They are required to master a wide range of medical services, so many in fact that if the US population of veterinarians all elected to specialize in much the same way doctors treat people, we would require over 500,000 vets to begin to cover all the various fields of expertise that we sometimes take for granted when we visit a veterinarian.

From birth (obstetrician) forward, your companion animal veterinarian must take care of a multitude of medical needs including surgery, dentistry, radiology, pathology, cardiology, gynecology, anesthesiology, urology, neurology, oncology, dietary and more. Additionally, compound these specialties with the individual needs of dogs, cats, birds, small animals, and reptiles and it becomes quite amazing to think about all the areas of medicine in which a veterinarian must be accomplished.

Veterinarians establish their practice in a variety of different forms. Some operate individual veterinary practices; others establish an animal hospital complete with equipment and staff equivalent to what you might find in a hospital for people. Some veterinarians specialize in emergency treatment while others offer more emerging veterinary services such as holistic medicine and pet psychiatry.

Choosing a veterinarian is similar to choosing your own doctor - except in most cases you aren't limited to making a choice from a list provided by your insurance company. It's wise to get recommendations from other pet parents and to visit the practice for a "get acquainted" session with the veterinarian. Several veterinary medical associations, such as AAHA (American Animal Hospital Association) and AVMA (American Veterinary Medical Association) have established membership guidelines for veterinary and facility standards.