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?
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 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 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.
· Plenty of this is synthesised by the dog to meet its needs.
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.
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
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.
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
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 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.
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.