- wo 14 sep 2005, 21:15
#386074
Unfortunately the comparison between cattle and sheep and their copper
requirements, although doubtless factual, bears little relevance to the
question of whether or not we should feed dogs a raw diet. Cattle and
sheep share a similar digestive physiology and they both consume a raw
rather than a cooked diet! On the other hand, the owners of some
Bedlington Terriers may well feel uncomfortable for the safety of their
dog's liver, when feeding their dogs on processed pet foods with their
high copper content!
Finally, in an endeavour to separate fact from fiction, note the
following. Firstly, it is true that for the time our dogs have been
associated with 'mankind who cooks,' some of the food that dogs have
eaten has been cooked. However, it is also true that in that period,
the bulk of the food which dogs have consumed, has continued to be raw -
scraps - mostly derived from mankind's 'rubbish heaps.' Indeed, it
has not been until the middle of the last century that the bulk of our
dogs' diet has consisted of cooked grain. This period of time is an
eye-blink in evolutionary terms, so that clearly, there has been no time
for the dog to adapt its digestive physiology to modern processed
foods. We may therefore conclude that the evolutionary diet of the
modern dog is one that aligns with the extensive practical experience of
Australian dog owners of the very recent past. That is, dogs not only
tolerate raw, but, in accord with the clinical observations of a number
of Australian vets (and many thousands of dog owners), actually require
most if not all of their food to be raw, in order to become and remain
truly healthy.
2) Do the enzymes in meat confer an advantage to raw fed dogs?
Unless one can demonstrate that raw meat contains digestive enzymes,
there is no reason to conclude that their presence may confer a
nutritional advantage. If by the presence of enzymes in raw meat, we
are speaking of the enzymes involved in the general metabolism of the
cell, the answer would have to be that such enzymes can not confer any
particular advantage! These enzymes function at a pH close to neutral
and have no function in digesting proteins, carbohydrates or fats,
rather they are involved in the citric acid cycle, the urea cycle and so
on. What scientists refer to as intermediary metabolism.
However, if we are speaking of the enzymes in lysosomes, then the answer
is, most definitely yes. Lysosomes are organelles found in all cells
and they contain digestive enzymes and that is a fact. Lysosomes have
numerous cleaning up functions within cells (including the removal of
potentially pathogenic bacteria) and they also have the responsibility
of digesting/destroying the cell, which contains them, when that cell is
no longer viable. Clearly, lysosomes are a concentrated source of
digestive enzymes. They function at a pH of 5 - a pH which they also
promote. The enzymes in lysosomes are the enzymes responsible for the
autolysis (self digestion) of dead tissue. We see (and smell) the
results of their activity in corpses left to 'rot' in the sun. That is
a definite and definitely unpleasant, fact.
It is not unreasonable therefore to surmise or hypothesise (and in fact
we know this to be true) that such enzymes are highly active at body
temperature and in an anoxic/acidic environment. This is precisely the
environment we find in a canid's stomach. In other words, yes,
lysosomal enzymes, released by every cell in raw meat, (but destroyed by
cooking) would play a significant role in the digestion of raw meat
within the stomach of a wild carnivore such as a feral dog, a wolf, a
dingo or a wild-cat.
Given that the digestive physiology of the wolf and the domestic dog are
essentially the same, we would have to conclude that lysosomal
digestion would definitely occur in the stomach of domestic dogs (and
cats), if allowed by the carer. Do those lysosomal enzymes confer a
health advantage? The answer to that is - we don't know, but since the
digestive physiology of canids over millions of years has evolved in
concert with the activity of lysosmes, our guess would have to be -
probably yes. I should also add at this point, that dogs, are gulpers
rather than chewers. This means they will send their raw protein into
the stomach in a form where the majority of the meat cells will be
protected from the highly acidic conditions of the stomach. This will
allow the lysosomal enzymes to continue their work at the desired pH -
of 5, for a period of time which would allow autolysis or lysosomal
digestion to play a more than token role in the digestive process of
canids.
In relation to the question (raised by HW) of trypsin inhibitors, while
it is true that raw soy beans contain trypsin inhibitors (and cooking
will destroy those inhibitors), no person contemplating a raw diet for
their dog would consider feeding it raw soy beans. On the other hand,
phytate, another antinutrient present in grain, is not significantly
affected by heat and will continue to interfere with the absorption of
certain minerals even after processing.
The thiamine story relates to a solo diet of raw fish flesh. It is the
case that some species (of fish) will contain a thiaminase. As no
competent raw feeder would bother to feed their dogs a solo diet of raw
fish flesh, the facts are, this is not a valid argument against feeding
raw.
The invalid raw egg white story has been around a long time. The
scientific fact is that there is sufficient biotin in the egg yolk to
more than compensate for the presence of avidin in the white, so in
practical terms, this is not a problem for the raw fed dog. Practical
experience bears this out. To produce a biotin deficiency, the facts
are, even by feeding pure egg whites and little else, it is almost
impossible to produce a biotin deficiency without also destroying the
gut flora with antibiotics. You see the fact is, healthy gut flora
produce all the biotin a dog requires.
In relation to cooking Vs acid denaturation of proteins, it is not a
fact that such processes are identical in outcome. While it is true
that cooking will denature the protein in a similar fashion to acid in
the stomach, the facts are, cooking will also destroy many other
nutrients which are not destroyed by the acid, including vitamins and
essential amino acids, so once again, this is not a valid argument for
cooking as opposed to feeding raw. Another sad fact about cooking is
that over-cooking (excessive heat applied to food for prolonged
periods), results in indigestible complexes between starches and
proteins - a common feature of cooked and processed pet foods, but
factually (and thankfully) absent in raw foods .
3) The question of maximising bioavailability?
Speaking from the standpoint of evolution, it would seem reasonable to
hypothesise that the bioavailability of nutrients as allowed by the diet
a species has eaten for millions of years, would by definition be
optimal. Such bioavailability will vary enormously from food to food and
from nutrient to nutrient. As this has been well demonstrated by HW, it
requires no further comment. Clearly, using maximal bioavailability as
a rationale for feeding a raw diet would most definitely be invalid and
therefore a poor reason for making the decision to feed a raw diet.
Equally, it is valid to speculate that evolutionary bioavailability may
well explain and confer some of the health advantage that raw-feeders
observe in their dogs.