by Amy Shojai
go moving the furniture, simple as that.”
Aging Ears
The normal feline ear can hear up to three times the range of sounds as
that of people. But with age, the delicate structures within the ear begin to
lose sensitivity to vibrations. This decline can be accelerated by damage
from very loud noises. Chronic ear infections or parasite infestations, such
as ear mites, may also damage the cat’s hearing.
Age-related hearing loss, termed presbycusis, shows up in any animal if
it lives long enough, says George Strain, DVM, a professor of
neuroscience at Louisiana State University. “There’s a certain loss of
nerve cel s with time in the body,” he says. Hearing loss can’t be reliably
predicted, but once it starts, it continues to get worse with time.
Cats can’t tel us they’re hard of hearing. “They compensate by paying
more attention to their other senses,” says Dr. Strain. “They may become
more visual y attentive, pay attention to vibration cues, air currents and
things like that.” Many times owners don’t recognize the cat has lost
hearing because it happens so gradual y, until suddenly they notice the cat
startles when touched or stops running to greet the doorbel .
Aging Taste
Changes in flavor perception are thought to reflect those
experienced by aging humans, says Nancy E. Rawson, Ph.D., of the Monel
Chemical Senses Center, a nonprofit research institute in Philadelphia
dedicated to research in the fields of taste, smel , chemical irritation and
nutrition. “But as a carnivore, the feline’s senses of taste and smel are
quite distinct from those of the human, and responses to age-associated
changes may differ,” says Dr. Rawson.
Cats aren’t able to detect carbohydrate sweeteners, but can taste
and seem to prefer meaty flavors described by people as “sweet.”
Detection of meaty, salty and sour flavors doesn’t seem to be affected by
age. Bitter tastes are more sensitive to aging changes.
Chemical irritations and “mouth feel” influence how wel the cat likes
or dislikes a flavor. These can be influenced by changes in saliva content,
for example, caused by dehydration that commonly develops in aged cats.
Disease or medication can reduce or increase the sensitivity of the mouth
and tongue, and alterations in taste (and smel ) can remain even after the
disease is cured and the medicine is stopped. Dental disease creates a
hypersensitive mouth, interferes with chewing ability, and produces
unpleasant tastes and odors that prompt the cat to refuse certain foods.
Warming foods increases the volatility of tastes and scents to make
them more intense and appealing to the aging cat’s palate. Antioxidants
hold promise for prevention of age-related scent and taste loss, says Dr.
Rawson.
Aging Nose
Scent is very important for cats, but few studies have documented
exactly what happens to its acuity in relation to age. Cats do lose smel ing
sense the older they get, but nobody knows the amount due to changes of
aging compared to lifetime damage, says Dr. Myers. “We’re just starting to
get a handle on how much the vomeronasal organ contributes to the total
scent picture for dogs and cats,” he says. The vomeronasal, or
Jacobson’s, organ is in the roof of the mouth between the soft palate and
nasal passages and is thought to be important in the detection of
pheromones, chemicals primarily involved in prompting sexual behaviors.
Snuffling foreign objects into the nose can cause damage. Upper
respiratory infections as wel as endocrine diseases such as diabetes and
hyperthyroidism also can damage the scenting apparatus. Age-related
losses in the sense of smel result from changes in the anatomy—scent
cel s aren’t replaced as often—and at the molecular level when existing
nerve cel s and “messenger” molecules in the nose become less sensitive.
Reduce salivation or altered nasal mucus composition also impact the way
odor chemicals are dissolved and detected, says Dr. Rawson.
“We did a study a number of years ago and published it in the annals of
the New York Academy of Sciences that dealt with the lack of the sense of
smel in the cat, and the influence of food intake,” says Dr. Myers. “A
complete loss of vomeronasal as wel as olfactory nerve caused the cats
not to eat at al . It seems as if the sense of smel gives them some sort of
cue that it’s edible,” he says. “A favorite veterinarian trick is get one of the
cheapest, nastiest, smel iest red tuna fish for cats when they stop eating.
That does seem to work in a fairly substantial number to start them eating
again.”
Bones and Muscles
By the time a cat becomes a senior citizen, her bones have begun to
lose density and become weaker and more brittle. That means senior cats
are more prone to fractures from fal s or leaps when they hit the ground.
Cats at thirteen to fourteen general y heal more slowly from a fracture,
says James L. Cook, DVM, an orthopedic surgeon at the University of
Missouri. “That’s when we start to see a lot of the manifestations from
arthritis with respect to the joints.” Slowed healing and bone loss likely are
due to the body’s slowed capacity to regenerate bone cel s.
“Orthopedical y, cats are real good healers,” says Dr. Cook.
The cartilage cushioning the joints wears thinner and becomes more
brittle over time, and the ligaments and tendons connecting the joints can
stretch, become less flexible, and tear more easily. Because cats weigh
much less than most dogs, the forces placed on bones and joints may not
cause as much damage over a lifetime of wear as in dogs, says Dr. Cook.
Obesity wil increase the risk for arthritis and strains and sprains.
Cats hide symptoms better, and that makes diagnosis more difficult.
“Cats are a little more stoic so the symptoms aren’t quite the same as in
dogs,” says Bil Fortney, DVM, director of community practice at Kansas
State University. Cats almost never limp or hold up a paw—they just hide
under the bed or refuse to move. “They may not groom themselves very
wel , they may be more irritable,” says Dr. Fortney.
Muscles become less able to use nutrition efficiently. Cats tend to slow
down as they age, and a reduction in exercise prompts not only a gradual
atrophy and loss of muscle mass but also contributes to bone loss. Older
cats that have less stamina and loss of muscle tone may not be able to
“make it” to the litter box in time. “Muscle mass is an extremely important
metabolic reservoir,” says Dan Carey, DVM, a veterinarian with the Iams
Company. The body uses muscle as an energy source during il ness.
Human studies show that il people with reduced muscle mass don’t
survive as wel as those with a healthy muscle mass, says Dr. Carey.
Digestion
The digestive system includes the mouth, teeth, stomach, intestines,
pancreas and liver. It processes nutrition and eliminates waste. One of the
greatest digestion-related problems of aging cats is obesity, or “over-
nutrition.” Older cats don�
��t exercise as much, and their metabolism slows
down, so they gain more weight.
However, because cats are true carnivores and use protein as a
source for energy, if they don’t eat enough, they’l lose weight as they age.
Cats may gain weight up to age ten, but then lose as they have less ability
to digest protein and fat. In fact, weight loss particularly of lean muscle,
tends to occur in cats at about two to two-and-a-half years prior to their
death from age-related diseases, says Joe Wakshlag, DVM, assistant
professor of clinical nutrition at Cornel University. He says studies in
otherwise normal adult cats indicate that increasing dietary protein by 35
percent (dry matter basis) enhanced lean muscle mass in these cats.
Geriatric animals have a decreased thirst response, according to
Alice Wolf, DVM, a professor of smal animal medicine and surgery at
Texas A&M (now Emeritus/Adjunct Professor). That means they are more
likely to become dehydrated when il , or even during routine boarding or
hospitalization. Aged cats also exhibit a general decrease in GI motility
and digestive enzymes and 20 to 30 percent of cats age 12 and older
have significantly reduced digestive function, says Wil iam Fortney, DVM,
an assistant professor at Kansas State University. The taste sensation is
also reduced, which can lead to anorexia—refusal to eat.
Probably the most common intestinal concern for aging cats is hairbal s.
Hair swal owed during self-grooming is normal y passed out of the body
with the feces. But because older cats may have more difficulty with motility
—movement of waste through the bowels—hairbal s can complicate the
problem and cause chronic vomiting or constipation.
Aging Teeth
Cats are prone to plaque and tartar formation on their teeth, just like
people. They don’t indulge in recreational chewing the way dogs do, but
may stil suffer from broken teeth especial y when the diseased tooth is
weakened by resorbtive lesions, a type of feline cavity. Tartar and plaque
buildup over time causes periodontal disease that can ultimately result in
loss of teeth and also impact the health of the rest of the body.
“Having periodontal disease is analogous to having an open wound,”
says Bil Gengler, DVM, a veterinary dentist at the University of Wisconsin.
Oftentimes the gum tissue is no longer attached to the tooth, and the root
and bone are exposed. “When that happens, those clusters of bacteria
travel through the bloodstream, and are filtered out at capil ary beds. This
process is cal ed bacterial showering,” says Dr. Gengler. The bacteria are
predominantly filtered out in the liver and the kidneys, and can damage
these organs. It can also lead to heart disease because of the bacteria-
laden blood passing over the valves of the heart.
Aging Stomach and Intestines
“The gastrointestinal tract in cats is relatively wel protected from the
ravages of time,” says Dr. Colin Burrows, an internist and professor of
medicine at the University of Florida. “In older cats, just as in older people,
the ability to digest diminishes somewhat but it’s not frightful y significant.”
Smal er but more frequent meals often help the cat’s body absorb more
nutrition.
“The only disease of note in the [older] cat that does not occur in the dog
is idiopathic megacolon. This is the constipated kitty,” says Dr. Burrows.
Megacolon is different than routine constipation, though, and develops as
a result of motility problems. The intestines lose their ability to move waste
out of the body.
Also, the bacterial population in the cat’s intestinal tract changes as she
ages, says Dr. Carey. “This isn’t as dramatic as in dogs, but in aging cats
it does shift toward the undesirable bacteria. In large part they are
diarrhea-type organisms that can invade the lining of the intestine,” he
says.
Chronic constipation or diarrhea are not specifical y “old cat” conditions.
Obesity, lack of exercise, and hairbal s can contribute to constipation. The
most common causes of colitis (inflammation of the colon) are stress,
which can lead to bacterial overgrowth within the colon. Cats are creatures
of habit and any change in their routine—adding a new pet, or working
longer hours, for example—may cause stress-related disorders. Cats may
also develop ulcers as a result of kidney disease.
To compensate for changes in digestion, therapeutic diets may help.
“Fat restriction may be beneficial because fat absorption and digestion
depends on enzymes that are found in the very tip of the vil i that line the
intestine, and this is the area that’s damaged first,” says Dr. Dottie
LaFlamme, a veterinary researcher with Nestle Purina PetCare Company.
“When you have damage to the intestine, fat malabsorption can occur, and
that can lead to worsening of problems.”
Aging Pancreas and Liver
The pancreas, located near the liver, produces enzymes vital to
digestion, and both the production of gastric and pancreatic secretions
decrease as the cat ages. Similarly, the enzymes produced by the liver for
metabolizing nutrients and detoxifying the body declines with age.
Inflammation of the pancreas, cal ed pancreatitis, is a recently
recognized disease of older cats, although the cause usual y is unknown.
Stricken cats often develop a triaditis, says Cynthia R. Leveil e-Webster,
DVM, an internist at Tufts University. That’s an inflammation in the
pancreas, intestines and liver al at the same time.
Overweight cats are especial y prone to a dangerous condition cal ed
hepatic lipidosis, or fatty liver disease, in which fat is moved into the liver
and interferes with its normal function. There are several other kinds of liver
disease, but the symptoms are al pretty vague and quite similar. “Owners
are not going to know that their animal has liver disease most of the time,”
says Dr. Webster. “And the doctor won’t know until after a lot of test.”
The liver continues to function wel , though, even when not at 100 percent
capacity. When a cat needs medication, however, there may be trouble.
“You need to be a little more cautious about medications with older
animals,” says Dr. Webster. “Old pets are often on multiple medications,
and drug interactions can affect how they are handled by the liver.” For
instance, certain drugs can inhibit the normal production of liver enzymes.
Therefore, if the liver is functioning at 70 percent and doing wel , but a drug
reduces that to 35 percent, the body may suffer the consequences.
Reduced efficiency compromises the old liver’s ability to metabolize
medications properly, among other things.
Endocrine System—Hormones
The endocrine system consists of a huge network of glands and organs
that produce hormones. The system includes the pituitary, thyroid,
parathyroid, pancreas, adrenals, ovaries and testes.
Hormones are a kind of “messenger” molecule secreted by endocrine
glands that are carried by the bloodstream to various distant body sites,
with instructions to alt
er that target tissue’s function—speed up or slow
down digestion, for instance. They are made either of protein or a type of
specialized fatty substance cal ed a steroid, and regulate body functions
and coordinate interactions between the different body systems. An
excess or deficient amount of a given hormone can cause disease.
Older cats slow down in part because their metabolic rate goes down,
says Dr. LaFlamme. Hormone imbalances become more common as the
cat ages because of normal wear and tear on the organs, and also
because age-related diseases like cancer often target the endocrine
system. The most common old-cat endocrine disorders are
hyperthyroidism and diabetes mel itus, discussed in Part 2 under their
alphabetic listings.
Heart and Lungs
The cardiovascular system carries oxygen and nutrients throughout
the body, and removes carbon dioxide and waste materials. The system
includes the heart, blood, and lymphatic system.
Old cats most often develop a heart disease cal ed cardiomyopathy,
which affects the muscle of the organ. It becomes harder for the heart to
work efficiently. Heart failure results when the damaged muscle is no
longer able to move blood throughout the body properly. Thromboembolic
disease can be a consequence, when blood clots form in the hind legs and
cause rear-end weakness, paralysis and pain due to lack of oxygen.
The respiratory system is composed of the nose, larynx, trachea,
bronchial passages and lungs. This delivery system supplies the body with
oxygen, and removes carbon dioxide.
The airways are exposed to damage caused by inhaled al ergens,
foreign bodies, viruses, bacteria and fungus and may result in a wide
range of problems. Senior cats are much more prone to upper respiratory
infections that can affect the lungs and/or nasal passages. For example, an
accumulation of fluid within the chest wal , cal ed pleural effusion, surrounds
the lungs and heart, and interferes with their ability to expand. Pleural
effusion is most commonly a result of heart failure. Pulmonary edema, fluid
within the lung itself, may develop as a result of cardiomyopathy,
pneumonia, or cancer.
Immunity
The immune system is composed of the spleen, thymus, bone marrow,