By Dr Clive Dalton
Unfortunately nutrition is not an easy
subject, and you can easily get lost in the technical detail.
The important point to remember
is that your working dog is an athlete and deserves more than a leg of frozen
mutton at the end of the day.
What a dog needs from its feed?
Carbohydrates
These are compounds made up of carbon,
hydrogen and oxygen and provide the "energy" part of the diet. They contain such things as sugars and
starch. The most complex
carbohydrates are broken down in digestion and end up as sugars before final
absorption.
Glycogen is carbohydrate stored in the
muscle ready for action. Marathon
runners have to build this up days before the race so they don't have to wait
for digestion to take place before energy can be used. Working dogs as athletes need this in a
big way too.
To get the energy out of the carbohydrates
the animal needs oxygen from the lungs via the blood stream. This burns up the carbohydrate
releasing carbon dioxide and water which is then excreted. Excess carbohydrates are stored in the
body as fat.
True carnivores don't need carbohydrates -
but dogs need them in a properly balanced diet. Carbohydrates should not exceed 60% of a dog's diet.
Dogs cannot digest large amount of fibre,
so cereals should be cooked before feeding or the dog will suffer from
diarrhoea. Too much lactose (milk
sugar) will also cause scouring so don't add large amounts of dried skim-milk
powder to the diet as it is 50% lactose.
Fresh milk contains only 5% lactose.
Proteins
Proteins are used for muscle building and
come from both animal and plant sources. The building blocks of these proteins are "amino
acids". The dog needs 23
amino acids but can synthesise (ie make its own) only 13, so 10 must be
supplied in its diet to prevent deficiency diseases.
The "complete" proteins that
contain these essential amino acids are found in eggs, milk, soybeans, peanuts,
yeast, as well as muscles and glandular organs. So the best way to make sure you have covered all the
essential amino acids in a diet is to use both animal and plant proteins in a
diet.
Proteins like carbohydrates and fats are
made up of carbon, hydrogen and oxygen.
But they have one important difference - they contain nitrogen. Proteins are insoluble in water so have
to be broken down by enzyme action into amino acids, which are then soluble and
easily transported around the body.
Animals can break down protein for energy
but this is not a very efficient process.
Surplus nitrogen produced in the process is excreted as urea in the
urine. To avoid this, make sure
dogs are not fed high protein diets over long periods, and there are enough
carbohydrates and fats in the diet to balance things up.
A dog should be fed protein daily as it is
not stored in the body in large quantities like fat. It should make up from 20 - 25% of the daily diet.
Fats
and oils
These are made up of chains of chemicals
called "fatty acids".
They contain carbon, hydrogen and oxygen just like carbohydrates, but
they differ by having a greater proportion of carbon in them. They also contain more than twice as
much energy on an equal weight basis.
So nature has designed fat depots to be
highly effective energy stores for times of need. You get a lot of energy into a small bulk! Putting fat on is a very efficient
process, for example the energy in 4 kg of starch to can be stored as 1kg of
fat. Taking fat off is harder, as
you only get 2kg of starch energy from 1kg of stored fat. Remember this when trying to slim down
an obese dog or to lose weight yourself!
Fat serves as important body insulation, as
well as helping to transport fat-soluble vitamins around the body. It also improves the palatability and
texture of dog foods. A
shortage of fat in a dog's diet can cause an abnormal skin and hair condition
and may increase susceptibility to skin infections.
A dog needs a minimum of 5% of fat in the
total dry weight of its diet. At
least 1% of the fatty acid called "linoleic" is needed for skin
health. If you feed the recommended
maintenance level of 20% fat, then enough linoleic will be present.
If you boost the fat level to 40% or more
this will provide all the dog's energy needs, but you'll risk problems with
rancidity. This can then impair
the utilisation of Vitamin E, cause deficiencies in the B-complex vitamins and
generally depress appetite. If the
dog doesn't eat, then it stops thriving.
So don’t expect top performance from all that fatty mutton - put it down
the offal hole and buy a decent balanced feed.
If you feed these high fat diets, then you
must readjust the mineral, vitamin and protein levels to keep the diet
balanced. You may also have to add
an "antioxidant" to preserve nutrient quality and stop the fats going
rancid. Avoid these problems by
feeding lower fat levels in the diet.
Vitamins
Vitamins are essential to growth and
health. They help the body to
resist disease and body cells to function properly. We have to consider two types of vitamins - water
soluble and fat soluble.
Water soluble vitamins
The B-complex and vitamin C are water
soluble. They cannot be stored in the body in large amounts so must be supplied
regularly in the diet.
When a dog loses fluids by vomiting or
diarrhoea, its vitamins must be replaced.. Overfeeding these water-soluble vitamins does not
cause toxicity as excesses are lost in the urine.
Vitamin B1 (thiamine)
·
This is very important to dogs.
·
Dogs differ genetically in
their need for thiamine.
·
Metabolic disturbance, exercise
and cold housing may increase demand.
·
Only small amounts of thiamine
are stored in the body.
·
Treating meat for hydatids
(freezing and boiling) reduces thiamine - it is lost in the thawed water and
boiling juices.
·
The heat of cooking will
destroy thiamin. Commercially
prepared dog feeds have extra thiamine added to their diets to compensate for
cooking losses.
·
If you are cooking your own
feed recipe, add some yeast tablets to it.
·
Feed a dog supplementary
thiamine 2-3 times a week.
·
Brewer's (not live) yeast and
wheat germ are valuable sources.
·
Meat and cereals are also good
sources.
·
A high fat diet contains less
thiamine than a high-carbohydrate diet.
·
Never feed dogs raw fish as
some species contain an enzyme (thiaminase) which will make thiamine unavailable. Nervous symptoms may develop leading to
paralysis. Cooked fish is safe as thiaminase is
destroyed.
Other vitamin B-complex
·
These include riboflavin (Vit
B2), niacin pyridoxin (Vit B6), pantothenic acid, biotin, folic acid, and
vitamin B12.
·
The best supplies are in wheat
germ, brewer's yeast, liver and the organ and muscle meats.
·
Under normal feeding there
should be no problems, but egg white and sulpha drugs can make them
unavailable.
·
"Black tongue" is a
defect of the mucous membranes caused by a niacin deficiency.
·
Poor blood clotting can be
caused by folic acid deficiency.
·
Riboflavin shortage can cause
slow growth, poor appetite and low fertility.
Vitamin C
·
Plenty of this is synthesised
by the dog to meet its needs.
Fat-soluble vitamins
These vitamins (A, D, E and K) need fat to
be transported and absorbed by the body.
So if the fat metabolism of the dog is upset, then a vitamin deficiency
may occur.
Get veterinary advice when supplementing
fat soluble vitamins as excess builds up and is stored in the body fat and can
lead to problems.
·
Liver, kidney, muscle fat and
fish liver oil are good sources.
·
Handle fats with care - the
vitamins are lost if the fat goes rancid.
·
Vitamin A deficiency results in
deafness, nervousness, diarrhoea, retarded growth and partial loss of vision (night blindness).
·
Excess vitamin A will lead to
bone deformities.
·
Vitamin D deficiency results in
rickets (bowed legs) and enlarged joints seen in pups growing quickly (knobbly knees
and splayed feet).
·
An excess of vitamin D will
lead to over calcification of bones and soft tissue such as heart, lungs
and muscles.
·
Vitamin E deficiency causes
pups to be born weak or dead. Can
lead to muscular dystrophy and hear muscle damage.
·
Vitamin K deficiency reduces
blood-clotting ability. It's rare
in normal diets.
Minerals
There is a range of minerals needed for
various functions of the body.
They are used in the skeleton (bones and teeth), muscles, glands, body
fluids and for correct functioning of the cells. Deficiency problems are easily avoided if you feed a balanced
diet. Commercial diets these days
provide more of these minerals than are needed by the dog so there are no
concerns.
Important minerals are:
Calcium Phosphorus Magnesium
Sodium Chlorine Potassium
If you ever see a feed analysis (eg. on the
bag of purchased dog feed), you’ll see a component called "ash". This is what’s left after the feed has
been burned to measure the heat or energy released. All the mineral components are in the remaining ash part.
Calcium and phosphorus
These two minerals are closely linked in
the health of the dog and are very important. We need to consider not only the amount fed, but also the
ration between them. This is
referred to as the Ca:P ratio.
The general recommended ratio in a good
diet for a mature dog is between 1.2 and 1.4 parts of calcium(Ca) to 12 part of
phosphorus (P).
Meat has a Ca:P ratio of about 1:10 while
liver has a 1:40 ratio. Liver is
also a good source of vitamins A and D which tends to modify the effects of a
calcium deficiency
·
Calcium deficiency is most
common bone disease in dogs caused by poor feeding. It
can happen by a shortage of calcium or an excess of phosphorus in the diet upsetting the
Ca:P ratio.
·
You won't fix a deficiency by
throwing your dog a few bones to chew!
Never feed a
dog cooked bones, fish bones or chicken bones.
·
Watch out for meat rich diets
which are high in P and low in Ca.
·
When the body tries to balance
up the Ca:P ratio, loss of bone mass which results in pain in the bones, joints and muscles
can occur. Lameness and a tendency
for bones
to fracture is seen , and in pups you get poor tooth development and sore and swollen
joints.
·
Pups should be reared on a diet
with a Ca:P ratio of 1.4:1. You
can ensure this by adding
bone flour or calcium phosphate at 15-20g/kg of dry food to the diet of a large rapidly
growing pup
Sodium
The dog will get plenty of this in its diet
as salt (sodium chloride), and often the concern is feeding too much. Providing plenty of water is essential
to avoid toxicity by feeding too much.
In very hot conditions, the dog may need extra salt.
Magnesium and potassium
These are important to the dog and can be
best provided by feeding liver, heart, or muscles in general.
Trace
elements
Some components of the dog's diet are only
needed in very small or "trace" amounts - hence the name trace
elements. Excess intake of some of
these can cause poisoning, or too much of one can affect absorption of another.
Iron
Sulphur Iodine
Copper Selenium Fluorine
Molybdenum Manganese Zinc
Cobalt
The way to avoid any problems is to feed a
good balanced diet. Seek
veterinary advice if you feel the need to add extra supplements.
Water
Water is not a strictly a nutrient but it's
essential to life. Muscle for
example contains 80% water, fat 20-30% and bone in a young animal 70-80%. Animals will survive for a long time
without feed but will soon dehydrate without water.
Blood, which transports all the digested
nutrients around the body, is largely water as is the lymph which finally
bathes the cells in nutrients.
Blood and lymph then carry the waste products away from the body cells
and tissues for excretion.
Water is the main constituent of all
digestive juices and gland secretions.
It's also a product of digestion when foodstuffs are broken down in the
body to produce heat and energy.
Dogs should always have a clean water
available at their kennels. There
will be a large variation in how much a dog will drink depending on its work
load and so on. Don't let a dog
drink large amounts of water just before or just after strenuous work. Frequent small drinks during work
are best and will increase endurance.
But it's hard to stop the dog diving into the creek on a hot day and
trying to drink it dry!
Digestibility
& Palatability?
When an animal eats feed, only some of the
nutrients in it end up in the blood stream to be used for maintenance and
production. These are the digested
nutrients and what is not used passes right through as indigestible into the
faeces. Large amounts of fibre for
example are not digested by the dog, but help intestinal function.
Palatability is how attractive the feed is
to the animal. Remember it's NOT
necessarily related to nutrient content.
Dogs eat because they like what they eat, and not because it's good for
them! Remember it’s your job to
balance the diet - not the dog’s.
Maintenance
and production
Think of dogs' nutritional needs in two
parts - "maintenance" and "production", as we do in other
farm animals. The maintenance part
of the diet is the feed nutrients needed to maintain healthy body functions
such as its temperature, digestion, blood flow, action of glands and excretion.
“Maintenance” needs are based on the dog's
liveweight, so regular weighing is useful to see if you have the feeding right. You can use the bathroom scales
weighing yourself with and without holding the dog. It's much easier on sheep scales.
The feed nutrients needed for “production”
are over and above the maintenance needs and include work, pregnancy, lactation
and growth.
What
does a dog like to eat?
This is an interesting question and you may
take the view that it's not important.
As a domesticated servant of mankind, a dog should eat what it's given!
Remember the dog's wild canid
ancestors. They survived best if
they devoured their food quickly and generally had either a feast or a
famine. Also, they ate
virtually anything - their diet varying from freshly-killed meat to rotten
stinking carrion. When they caught
prey, they usually started on the guts first - warm and sloppy. They certainly preferred
"variety" and this has been confirmed by properly controlled
scientific trials at Massey University.
Where dogs were given a free choice of food
and their preferences measured, there were some surprises! Researchers found that dogs prefer pork
and beef to mutton, cooked meat is preferred to raw meat, and ground meat is
preferred to chunks. Dogs also
prefer their food warm, wet and sweet.
Now remember this says nothing about
nutritional value - all it says is what a dog prefers, if given the
choice. The work removed the bias
of a person making decisions for the dog, which is not very realistic,
especially in the supermarket.
But it's people
who decide what dogs eat in our modern lives these days. Studies at the Meat Research Institute
in Hamilton showed that pet foods have to be made attractive to the owner of
the animal! So things like rich
colour, juiciness and chunkiness suggesting good flavour are essential - not
for the dog but for the owner who imagines the pet feels like they do! This may not be the case if you
want to be truly objective and avoid being “anthropomorphic” or judging animal
feelings by human feelings.
It is quite
normal for dogs to eat grass and their own vomit. Indeed, eating grass irritates the stomach and encourages
vomiting. Dogs enjoy
scavenging and will eat their own faeces (coprophargy), and sheep’s faeces, as
one of nature's ways to make sure they get all the minor trace elements and
vitamins needed.
Feed
aversions
The instinct to
avoid certain feeds is interesting and you see it best in wild canids. They use aversion to foods to learn to
avoid poisons. If young wolves for
example eat berries that make them ill, they know not to eat them again. This is how they learn. If a dog learns to associate a food
with a bad experience, it will never eat it again. It's an inbuilt survival mechanism that can be a nuisance at
times when you’ve gone to a lot of bother to provide a feed and they won’t eat
it.
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