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| How much do you know about small animal nutrition? |
Do you know enough about companion
animal nutrition? Professor David Fraser AM is a giant in the field of
nutrition and a world-expert on vitamin D (sometimes we don’t know how
important these things are til we have a relative excess or deficiency). Nutrition
impacts animal health and welfare, and is always the subject of vigorous, heated debate within and outside our profession. Professor Fraser answered our questions
about nutrition.
In what key ways does small animal nutrition differ from human
nutrition?
In general human and dog and cat nutrition are
rather similar. However, there are differences and in particular there are
differences between dog and cat nutrition.
A major difference between nutrition of these
animals and the human is in calcium and phosphorus requirements. All
animals (including the human) have the ability to adapt to a shortfall in the
calcium content of the food they eat. Provided that they have adequate
vitamin D status the capacity for absorbing calcium from food can be increased
so that an absolute percentage of calcium in food is not needed. Flexibility in
absorption capacity can compensate for variation in calcium content over quite
a wide range.
However, and here is the big difference with
humans, the calcium and phosphorus in the food of cats and dogs (and other
domestic animals) has to be in the range of 1:1 to 2:1 calcium to phosphorus on
a weight basis. If the ratio is outside that range, particularly during
growth, then severe bone undermineralisation and deformity will occur. In
contrast, such a relationship between the need for calcium and phosphorus in
human diets does not seem to exist. The typical western diet is high in
phosphorus and low in calcium and no harmful consequences seem to follow.
If such a diet were fed as the only food to dogs
and cats they would develop bone disease, which in the jaws would lead to loss
of teeth and gingivitis. Before commercial pet foods became widely used
in the feeding of dogs and cats, these animals were fed essentially on meat
alone – high in phosphorus, very low in calcium. As a results defective
bones and teeth were frequently seen in veterinary practice.
Another thing to note is that the cat most
certainly and the dog, probably, are unable to obtain vitamin D from solar UV
irradiation of skin. They therefore need a dietary supply of this
substance. The human on the other hand, eats foods that contain trivial amounts
of vitamin D and depends almost entirely on exposure of skin to sunlight in
order to acquire vitamin D.
The other thing to note is that the dog is a
carnivorous omnivore, whereas the cat is an obligate carnivore. This
imposes differences on their nutrient requirements. The cat has a higher
protein requirement than the dog as it needs dietary amino acids to convert to
glucose to maintain blood glucose concentration. The cat also has a whole
host of micronutrients that it has to get from food, whereas the dog is able to
make a lot of these. E.g. the cat requires a dietary source of preformed
vitamin A, taurine, nicotinic acid, and gamma linolenic acid and arachidonic
acid. The cat also has higher requirements than dogs for sulphur
containing amino acids and arginine. These are all related to changes in
metabolic processes associated with being entirely dependent on food from
eating other animals.
What are the consequences of feeding a poor diet to dogs and cats?
This depends really on what is a poor diet.
The points in the above answer cover a lot of what could be considered poor
diets. Perhaps the major types of poor diets are those which provide
insufficient protein or too much or too little metabolisable energy.
Too little protein, particularly for cats will
result in muscle wasting as non-essential proteins are broken down to supply
amino acids for proteins essential for survival. The energy density of food for
dogs and cats should ideally range from 4 to 4.5 kcal metabolisable energy (ME)
per gram of dry matter. If the energy concentration is below that range,
dogs in particular may not be able to increase their food intake to provide
them with enough ME and so they will lose weight.
A more significant problem is if the energy density
is well above 4.5 kcal ME/g, particularly if the food is highly
palatable. Dogs and cats will be inclined to eat more of such food than
is needed to meet their energy expenditure and they will gain weight and eventually
become obese. I suspect that the increase in prevalence of obesity of dogs and
cats is a combination of the excess consumption of very palatable foods and
lack of physical exercise. Commercial foods compete with each other
mainly on the basis of palatability. Hence overeating is likely to result
when a dog or cat likes a particular brand of food and it is provided by its
owner in ad libitum amounts.
Has the advent of premium pet foods solved nutritional problems in
animals? If not, why not?
I suspect that all pet foods on the market are
formulated to match the AAFCO feeding standards for each species. There
may be differences in the digestibility of some food components – an increase
in the amount of vegetable or cereal matter in a food may decrease the digestibility.
Premium pet foods probably have higher proportions
of the type of foodstuffs that dogs and cats would be eating in the wild.
They almost certainly have very high palatability that would help to confirm
that the dog or cat eating them considers they are close to their ideal
food.
However, I think that analysis for all the
essential nutrients would show that the premium foods are quite similar to
those that are cheaper.
Why do you think it is important for vets to learn more about nutrition?
Nutritional knowledge can be used not just to
advise on how to feed a particular species of animal but also it can help in
the diagnosis and treatment of disease. In the early 1980’s a survey was
done by, I think the Australian Veterinary Association, of vets who had graduated five years earlier. They
were asked what aspect of their veterinary science course could have been
improved, in the light of their experience in veterinary practice.
A frequent response was that they felt that
nutrition was appallingly taught because they found that they frequently needed
nutritional knowledge and it wasn’t there. In actual fact, nutrition had
been well taught in the BVSc degree at that time, but it was a second year
subject. By the time students were learning clinical veterinary medicine,
their memory of nutrition was fading and by the time they graduated it had
virtually disappeared [Ed: That was my
experience too]. Nutrition is really a subject that should be taught
in an integrated way with clinical veterinary medicine so that its relevance
can be more easily understood and thus, more likely to be part of the mental
framework of being a veterinarian.
Do you have any advice for vets or future vets about nutrition?
Wow! I wouldn’t presume to provide any advice other
than the general point that veterinary medicine is applied comparative
biology. By having a good understanding of the knowledge of how healthy
animals function in all aspects of their lives and also the differences between
species, the detection and correction of abnormalities in those functions would
be more readily done. Understanding the principles of nutrition and how
malnutrition can occur should be part of the mental framework of a vet,
regardless of the career path they are following.
Professor Fraser is teaching a short, online course on small animal
nutrition through the Centre for Veterinary Education. For more information
visit here.
