Accounting for Taste

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Account ingfor

Susan ran to catch up with Scooter, her Norwich Terrier, as he

trotted proudly along the hiking trail with a greenish-brown

object in his mou th. "What d o you have?" she dem anded.

Sensing that Susan was going to take his prize away, Scooter stopped

and began munc hing the clum p of horse man ure as fast as he could.Susan fought a losing battle as she tried to pick the slimy pieces

of half-digested hay out of her dog's mouth. "Yuck! I can't believe

you like the taste of that stuff!" Susan exclaimed as she wiped her

hands on he r jeans.

Dogs have incredibly flexible food preferences. After all, they are

adaptable carnivores that evolved over approximately 100,000 years

eating the refuse of human civilization. If they couldn't catch a rat,

they could always scavenge bits of creatures killed by humans or

other animals. But what makes a dog gulp down rotten goose eggs

with a delighted grin on its face (often followed by a sulfurous burp),

yet turn its head away ft-om a dog food advertised as "specially formu -

lated for the discriminating dog?"

Bud behavior

It starts with the taste buds. Unlike humans, who have 9,000 taste

buds, dogs have only 1,700. However, a dog's super-acute sense of

smell likely compensates for its relative dearth of taste buds. As anyone

who has suffered a cold know s, the ability to smell is an imp orta nt

part of being able to taste.

Dogs' taste buds sense the five universally recognized

tastes: salt, acid, bitter, sweet and savory. Different taste bu ds

are localized to different areas of the tongue and throat.

The front two-thirds of the tongue tastes saltiness, the

back one-third senses bitter substances and the pharynx

(the part of the throat that leads to the esophagus) and

larynx (the part of the throat that leads to the trachea)

identify sweetness. Taste bud s for acidic and savory fla-

vors are distributed all over the tongue.

The taste buds are sensory receptors made up of

clumps of cells that have special surface molecules.

Each cell senses just one type of taste. The taste buds

that sense salt and acid have channels in the cell me m-

brane through which sal ts

and acids travel from the Dogs enjoy variety in their

cell's ou tsid e to its insid e, diet s-a n instinct thatBuds that .sense bitter, sweet likelymotivated them to

and savo ry tastes have recep- seek out multiple food

Why dogs eat

strange things

and other

interesting facts

abo ut the canine

sense of taste .

B Y M . C H R I S T I N E

Z I N K , D V M , P H . D .

proteins that clamp on to taste molecules and transport them across

the cell membrane to the inside of the cell.

Once the flavor molecule is inside the cell, serotonin, a message

molecule known as a neurotransm itter, is secreted by the cell. Sero-

tonin triggers one of three sensory nerves - the facial, glossopharyn-geal or vagus nerves - depending on w hich part of the tongue and

mouth the taste bud resides. The nerve sends messages to the brain

where the specific taste is recorded. Information regarding the tbod's

taste and smell is processed, along with any memories or associations

the dog has of eating the food in the past, to provide an overall posi-

tive or negative experience of eating.

For example, if an ill dog experiences nausea immediately after

eating fish, it might refuse to eat fish for weeks or months afterward

because of the negative association. Likewise, if a puppy is given lots

of sweet doggie junk-

food treats, it

might prefer

the taste



of sweets for the rest of its life, espe-

cially if it is occasionally rewarded for

good behavior with a sweet treat.

What tastes meanDogs have a special love for sweet

foods. This is in c ontrast to cats, which

do not have tas te buds that detect

sweetness {not surprising because they

are obligate carnivores, meaning that

the majority of their diet must consist

of meat). To dogs, sweel taste might

indicate a highly acceptable, energy-rich

food source - possibly a survival m ech-

anism inherited from their ancestors.

According to Nicola Ackerman,

BSc, RVN, Cert. SAN, in her hook

Companion Animal N utrition (Butter-

worth-Heinemann, 200S), scientists

have demonstrated that female dogs

enjoy sweet foods more than male

dogs, perhaps because of the impor-

tance of providing enough energy to support a litter of puppies.

Unfortunately, some human foods that are toxic to dogs (such as

chocolate) have a sweet flavor. The love of sweet-tasting items also

induces dogs to lick highly toxic antifreeze that has leaked onto the

floor of a garage.

In addition to making eating enjoyable and differentiating one

food from another, the taste buds have another function - saving

the dog's life. The bitter taste buds warn dogs of potentially toxic

substances (almost every naturally occurring toxin tastes bitter).

Whe n a dog eats a toxic plant or be rry, for exam ple, the bitter taste

will cause the dog to spit the food out and perhaps vomit any that

was already swallowed.The one taste that dogs are relatively insensitive to is salt. This is

likely because a carnivo re's diet generally con tains sufficient salt for

survival and there is no need for a dog to specifically seek out salts

to supple men t th e diet, the way grass-eating animals like cows and

deer must do.

Dog food formulasNot surprisingly, dog food manufacturers have performed extensive

studies on dogs' sense of taste in an effort to make the most palatable

A (luy % rood préférences likely begin büun dfler bir iii diiu dre influenced by tne adm ^ diei .

foods. They and others have designed elaborate taste-testing protocols

in which dogs are trained by opérant conditioning to indicate thei

preferred foods.

In the study, "A novel cognitive palatability assessment protoco

for dogs," dogs were rewarded for choosing a certain food, then given

novel food (I.A. Araujo and N.W. Milgram, journal of Animal Scienc

July 2004). The novel food was considered more palatable if the dog

chose it over the food for which it had been rewarded.

Another study, "Preferences of dogs for various meats," showe

that dogs prefer the taste of cooked meat over raw and that they enjo

some meats better than others (C.L. Lohse, Joumal of the America

Animal Hospital Association, 1974).In general, dogs prefer the following protein sources in declinin

order: beef, pork, lamb, chicken, horsemeat ("The role of olfaction in

canine food preferences," K.A. Houpt, H.R Hintz and P. Shepherd

Chemical Senses, 1978).

Studies have also shown that preferences for particular food

likely start soon after birth, based on what the mother eats ("Th

evolutionary basis for the feeding behavior of domestic dogs an

cats," John W.S. Bradshaw, The Journal of N utrition, July 2006 ). Thi

as well as positive or negative associations with food, likely account

for differences in food preferences of individual d ogs.

According to some studies, dogs fed the same food all the tim

suffer a monotony effect; they gradually lose their appetites. Thi

quickly can be reversed by providing novel foods. This need for a var

ety of foods likely played an essential function before the age of do

food in helping dogs seek out mu ltiple food sources, thus reducing th

likelihood of nutritional deficiencies. When Scooter scarfed down th

horse poo p, he was simply enjoying a novel food.

Losing tasteSeveral diseases can affect a dog's sense of taste. Dogs with hypothy

roidism are thought to suffer from a decreased sense of both taste an

smell. This is important given the high incidence of hypothyroidism

in many dog breeds and the condition's increasing incidence th

longer a dog lives.

Some anti-cancer drugs can also alter this sense. This is par



molecules that cause dogs to lose weight. This d ou-

b le h i t resu l t s in a con d i t ion know n as cancer

cachexia - a profound loss of body weight and mus-

cle mass.

Dogs with chronic renal failure don't sense taste

for sweet things w ell. This likely is because waste p rod-

ucts in the blood can cause nausea, as well as mouth

ulcers and infections.

Many otber conditions can cause a dog to lose its

sense of taste. Dogs with diabetes have a reduced sen-

sitivity for all five tastes, possibly because this cond i-

tion damages the peripheral nerves. A dog that expe-

riences cranial trauma, from being hit by a car for

example, may lose its sense of taste. Usually tempo-

rary, taste returns as the brain beals and reforms its neural connec-

tions. Depression can cause reduced sensitivity to taste because of

serotonin's importance in sending taste messages to the brain. Sero-

tonin levels usually are lower in animals w ith depression.

Certain therapeutic drugs can affect taste, too. For example,

doxycycline (the antibiotic of choice for dogs that test positive for

tick-borne diseases, such as Lyme disease and Rocky Mountain

spotted fever), can cause a dog to temporarily lose the ability totaste or to experience abn orm al taste sensations, such as metallic-

tasting food.

W hetting the app etiteTbe palatability of a dog's food can be increased by adding moisture

(which increases the food's odor), fat, protein, sugar or salt (in rea-

sonable amounts), and also by adding particularly aromatic flavors,

such as garlic salt. One excellent way to give your dog's food a gour-

met taste is to marin ate it in sweet fruit juices, sweet and sour sauces,

or yogurt w ith garlic and ginger paste.

One or more of these simple dietary modifications can be helpful

for dogs that have lost their appetite due to illness or dogs tbat musteat a special diet. For example, the add ition of garlic or a novel source

of carbohydrates, such as strawberries, can help a dog with renal fail-

ure enjoy a low-protein diet and thus prolong its life.

Peculiar preferencesWhen it comes to your dog's propen-

sity to give you a big wet slurp on

D o g s a r e d r a w n t o s w e e t - ta s t i n g

f o o d s , w h i c h c a n b e g o o d

s o u rc e s o f e n e r g y w h e n

m e a t is s c a r c e .

S t u d i e s h a v e s h o w n

t h a t d o g s p r e f e r t h e t a s t e o f so m e m e a t s m o r e t h a n o t h e r s .

the face after visiting the kitty litter box for a midday snack or dining

on poopsicles during winter, it might be best to keep what's out of

sight out of m ind.

If you prevent your dog from having access to those caninedelights, it will likely choose more accessible fare, such as the loaf of

freshly baked bread left out on the counter or the dense, lush grass

growing in the shadows by the house.

Flavor friendsWhere taste is concerned, our canine companions aren't all that

different from us. Dogs' taste buds fun ction biochemically just

like humans' and like us, dogs have tbeir favorite and not-so-

favorite foods.

Dogs love to eat and most prefer to eat until they are quite full.

The major difference is that tbeir taste preferences are those of a car-

nivore, modified by tens of thousands of years of eating leftovers

from our tables and scavenging waste from human communities.

What a perfect collaborative relationship! /f

M . C h r i s t in e l i n k , D V M , P h . D . , p r e s e n t s C o a c h i n g th e C a n i

A t h l e te s e m i n a r s w o r ld w i d e , a n d i s a c o n s u l t a n t

o n c a n i n e s p o r ts m e d i c in e , e v a l u a t in g

c a n i n e s t r u c tu r e a n d l o c o m o t io n .

Accounting for Taste

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