Taurine, an organic acid which is found in all animal tissues, is not degraded by the freeze-thaw process when it comes to raw meats, however it is degraded when it is cooked or exposed to heat of some kind.
Cooked Meat
Feeding cooked meat, especially if you have made it homemade is a huge risk to your obligate carnivore since Taurine is essential for your ferrets overall health and is lost during the cooking process. Cooking in general causes a loss in many nutrients. Enzymes are destroyed by cooking.
Digestive enzymes are produced primarily in the pancreas and released into the duodenum to help digest food coming from the stomach. However since Digestive enzymes are destroyed during cooking, the chore is left to the intestines or the pancreas themselves to secrete amylase and other digestive enzymes. Enzymes are important. They don’t just help to digest the food – they are living proteins that help repair DNA, make hormones, prevent clotting and so on. Eating a diet of cooked and processed foods would put incredible stress on our ferret's bodies. The pancreas in particular, since it has to produce massive quantities of digestive enzymes after consuming a food that is devoid of enzymes.
Long term consumption of a diet consisting of completely cooked meat can lead to alot of over worked organs, which can then lead to very horrible diseases. This does not mean that you cannot feed cooked meat though. It is recommended to be only a treat, not something that is the entire diet. Never feed cooked bones to your ferrets as they can pose a serious risk. Once the bone in meat has gone through the cooking process, it can remove the nutritional value of the meat and the bones become more brittle, increasing the risk of splintering.
Can Ferrets synthesise Taurine?
Obligate carnivores are not able to synthesise all the taurine they need from other amino acids (such as methionine and cysteine) unlike some other carnivores and unlike herbivores or omnivores. This means that it is essential to their diet and must be fed to the ferret.
What is the role of Taurine?
Taurine is a major constituent of bile and can be found in the large intestine. Taurine has many fundamental biological roles, such as conjugation of bile acids, anti-oxidation, osmoregulation, membrane stabilisation, and modulation of calcium singling. It is essential for cardiovascular function, and development and function of skeletal muscle, the retina, and the central nervous system.
Is Taurine an Amino Acid?
Taurine is unusual among biological molecules in being a sulfonic acid, while the vast majority of biologically occurring acids contain the more weakly acidic carboxyl group. While taurine is sometimes called an amino acid, and indeed is an acid containing an amino group, it is not an amino acid in the usual biochemical meaning of the term, which refers to compounds containing both an amino and a carboxyl group.
What may happen if Taurine is not in the diet?
A diet that does not have enough taurine can cause the heart to stretch and enlarge (dilated cardiomyopathy). This can lead to congestive heart failure and in worse cases, death. In the eye, a low taurine diet can cause blindness from central retinal degeneration. In order for any issue to arise, a Deficiency must drag on for a certain length time. It may take months, it may take years, it all depends on the ferret.
Can I feed too much Taurine?
Taurine is a water soluble nutrient, so that makes it incredibly rare that a ferret would overdose on Taurine. If a ferret eats something and there is too much taurine in it, the excess is simply excreted VIA urine.
I will give you another lesson on Water Soluble and Fat Soluble Vitamins another day.
So where can Taurine be found?
The main source of Taurine for our ferrets in the Frankenprey menu is Hearts. Taurine can also be found in other types of meat, but hearts are essential to insure they get an appropriate amount of Taurine in their diet. If you cannot find hearts or need another option, brain, and tongue also have a high amount of Taurine. Raw (beef) tongue is also the next best option to hearts as it is very high in Taurine. In fact, Tongue has a higher amount of Taurine than that of Heart and is also quite fatty. Beef tongue is a good option if you can find it or if it is in your budget.
If you cannot locate a Heart, or Tongue, Supplementing with a Taurine powder can be used short term until you can find alternative sources for Taurine. A health food store should have Taurine powder. It may be handy to have stored away for emergencies. Supplementing Taurine is 500mg/Day per ferret.
This thread has some good information on Supplementing with Taurine Powder/Capsules. holisticferret60.proboards.com/thread/13404/little-education-on-taurine
Vitamins or nutrients are classified as either Fat-soluble (vitamins A, D, E and K) or Water-soluble (vitamins B and C).
The Fat-soluble vitamins / nutrients are soluble in lipids (fats). Fat-soluble vitamins, especially vitamins A and E, are stored in body tissues. They are stored primarily in the liver and in fatty (adipose) tissues. Extra care must be taken to not consume these vitamins in excess because they stay in the body longer and can more easily lead to toxicity. A well-balanced diet will not lead to toxicity, but vitamin supplementation might. An example of a Fat-soluble nutrient is Vitamin A. Vitamin A can be found in high concentrated amounts in the Liver. This is why we discourage any unnecessary treats or supplementation that contains Liver or Vitamin A due to the high risk of Toxicity. If you have a well-balanced menu and diet planned out for your ferret, then you have no need for supplementation.
Water-soluble vitamins, which include all of the B vitamins, are easily absorbed into the body. If your ferret was to consume more of a water-soluble vitamin than it needs, the excess will be excreted VIA urine, rather than stored within the body. This means the risk of an overdose is relatively low, but you will have to constantly replenish your stock through the diet. A good example for a water-soluble nutrient is Taurine. Taurine can be found in heart, tongue and brain in highly concentrated amounts.
Recommended Reading: Vitamins and Minerals in Raw: http://holisticferretforum.com/natural-diet/truth-about-diet/vitamins-and-minerals-in-raw/ Vitamins: http://holisticferret60.proboards.com/thread/1222/vitamins#ixzz3zGVSVOYV Basic Frankenprey Menu: http://holisticferretforum.com/natural-diet/raw-diet-the-meat-of-the-site/basic-frankenprey-menu/
Some –If not all– Organs smell, look and feel just plain horrid, But they are essential for a healthy and balanced diet for our beloved ferrets. Regardless of our human diet choices, It is our responsibility to provide for our ferrets without biased views or specific feelings towards meat.
Being Veg And Feeding Raw
Pork Kidney
Yes, you can be vegetarian, or vegan and still give your ferret a species appropriate diet. It just takes little more effort, especially if you're particularly squeamish around meats. The main thing for vegans would particularly be around finding the source of the meats, especially if you are not not happy and do not wish to support the majority of the cruelty behind the meat industry. It can be done, even though animals must be sacrificed for our ferrets, but providing that they are cared for and killed humanely, then that should put you at ease to some degree.
I myself am a Vegetarian, and I know plenty of vegans who also follow a frankenprey (and or) whole prey diet for their obligate carnivores. But that is another topic and for now I wills tick to simply speaking about organs.
Organ's In Ferret Nutrition
Organs, also commonly called offals or variety/organ meats, refers to the internal organs and entrails of a butchered animal. Some organs are even used in various meals for human consumption in certain countries.
Lamb Liver, Also common referred to as Lamb Fry in various countries.
In regards to the frankenprey diet, you will need 10% organs in your ferret's total weekly diet. That is 5% of Liver, and 5% of another organ. The reason as to why the liver is only 5% is quite simple. Liver contains vitamin A.Vitamin A is a fat soluble vitamin, and if fed in excessive or too frequent amounts it has the potential to cause toxicity in ferrets.
Fat Soluble Vitamins?
The fat soluble vitamins are soluble in lipids (fats). Fat soluble vitamins, especially vitamins A and E, are stored in body tissues. They are stored primarily in the liver and in fatty (adipose) tissues. The fat-soluble vitamins include A, D, E, and K. Extra care must be taken to not let your ferret consume any of these vitamins in excess amounts either too frequent feedings, or in large meals because they stay in the body longer and can more easily lead to toxicity. A well-balanced diet should in no way lead to toxicity issues, but vitamin supplementation on top of a well balanced diet might.
It's An Organ, But Not An Organ?!
Even though it is technically an "organ" body wise, The Lungs in raw feeding are not considered an Organ. However It can be fed in an organ meal every once in a while. It just cannot replace other secreting organs.
Keep in mind that there are certain organs which are not considered "organs" nutrition wise when it comes to raw feeding. For the basic frankenprey diet, you want to feed secreting organs as part of your typical 10% organ meals. It does sound quite confusing, but don't fret. It's quite simple once you do your research and study!
To sum it down-- a few things which are "not considered organs" are things such as Gizzard, Tongue and the Lungs. I highly suggest that you check out the Holistic Ferret Article on Organs for a more in-depth article on the organ subject.
Heart is also not considered an organ. It is fed as a muscle meat and is required in the diet on a weekly basis to ensure enough Taurine is in the diet.
These are Turkey gizzards, they too like the lung are not considered organs in raw feeding nutritionally wise. However these are considered a muscle meat, and make a perfect chewy meal for your ferret. They help to build jaw strength, and would make a perfect meat for new to bone in meat, ferrets.
Organs And Availability
As for organs which you can use, the most commonly found organs are Liver and Kidney, possibly even Pancreas. However, even though these are considered common where I am, it may depend on your location as to what is more common for you. For example, I personally cannot find anything other than Liver or Kidney where I live, however if I was to travel to the Markets in Preston (Australia) then I would find a good variety of other organs such as Spleens etc. You "Hopefully" should at least be able to find any two organs, if not then I highly suggest that you talk with your local butcher, supermarket or local meat market and enquire on if they are able to order any specific organs for you. If they cannot, don't give up on your organ hunt, ask around. You may even be able to directly purchase from abattoirs or farms. If you've looked everywhere and still cannot find at least the Liver and one "other secreting" organ, then try ordering online and in bulk if you have the freezer space to do so. The more variety regardless of the meal, the more nutritious the diet will be for your ferret.
Remember, not all proteins, not all types of meat or organs will hold the exact same nutrition stats. Some will have vitamins and minerals in varied amounts. This is another reason as to why variety is the key to a well balanced diet. The more types of food fed, the more the ferret gets a variety of nutrients to help support life.
I only use two organs currently, Liver and Kidney, Since that is all that's available where I live. Liver is needed in small amounts for a base diet as seen in the typical Frankenprey menu (Which can be found here). Liver is best paired with at least one other organ. You don't necessarily have to use kidney, so use which ever other organs are available to you. Remember, the more the better for your ferret's overall health.
Pork Brains
Serving Organs
The organs can be served in a variety of ways. If you have a single ferret, feel free to simply serve as it is or diced up. If you have 2 or more ferrets it would be wise to puree or blend the organs as a soupie. Although its not essential, its a good option especially if you're busy. It's also incredibly convenient and balanced, so it ensures that no ferrets consume one organ more than the other. If you don't wish to puree it, that's fine, you may also feed one organ at a time. I sometimes do this when I'm home. So in the morning I may feed liver and at lunch time I will give them a kidney. Both times I will add some hearts along with it. You don't have to worry too much about hearts since the Taurine in hearts are water soluble, meaning they can consume plenty of heart and simply excrete any excess nutrients VIA their urine. When I'm busy and cannot be home, I simply puree it and leave the hearts diced. It makes it kind of like a chunky organ soup. :) If you are having trouble with getting ferrets to consume organs during a transition, be repetitive and dab some on their gum or lips. The more you do it, the more they will lick it and become used tot he taste and smells. Another method would be to blend an egg into the organ meals. I find that this something alters the strong odours or tastes, and ferrets may enjoy the extra taste. :)
Pork Testicles
Culinary Names?
Some organs are called by certain culinary names in various countries.
For example, Sweetbreadsorrisareculinary namesfor thethymus(also called throat, gullet, or neck sweetbread) or thepancreas(also called heart, stomach, or belly sweetbread), especially ofcalf(ris de veau) andlamb(ris d'agneau), and, less commonly, ofbeefandpork.The "heart" sweetbreads are more spherical in shape, and surrounded symmetrically by the "throat" sweetbreads, which are more cylindrical in shape.
(Some other glands used as food may also sometimes be called "sweetbreads," including the parotid gland ("cheek" or "ear" sweetbread), the sublingual glands ("tongue" sweetbreads or "throat bread"), and testicles (cf. Rocky Mountain oyster, prairie oyster, or lamb fries)
In Australia and New Zealand, lamb's fry is specifically the liver; in the United States, "lamb fries" (q.v.) are specifically the testicles. In the U.K., it was all offal, though recently testicle has become rare.
In Conclusion,
Organs are essential for the overall health of your ferret. Some proteins and organs may contain more or less of various nutrients, so variety and balance is the key to maintaining your ferret's health and diet. Organs may be known as certain culinary names in certain countries, but when in doubt ask a butcher and you should be able to "hopefully" locate the organ of your choice. If you can get a variety of different organs, I suggest you do so. Find your own way to serve your organ, and keep them as 10% of the overall frankenprey diet. That is 5% liver and 5% other secreting organ. For more information on organs, or if you have concerns or questions in regards to organs and or the species appropriate diet, please come and join us on the Holistic Ferret Forum, or feel free to send me an email, or leave a comment on my blog.
Good morning everyone! It's actually 2AM and I should be sleeping, but I wanted to talk about something. On the 12th of December I randomly decided to cut up some steak and try myself with some freeze dried raw. This is my first time and it really turned out quite well. It took little over 6 weeks before my beef rump steak had completely dried out. Silly me however, Cut them too large in size, so It may have taken me a lot longer than I was expecting it to. Even for cooked meat, I usually takes me about 3-4 weeks.
I checked for moisture before I thawed a piece, and none was found. I tried again after I thawed a piece and again, no moisture so it turned out perfect. As you can see in my photo above this blog entry, I have some fat in there. The rump steak had a long strip of fat and there's no use wasting it since ferrets can use the fat for energy. The fat itself felt smooth and somewhat oily in texture, I'm probably not explaining it correctly rofl. I did try them out with Haru (my little sable female) and she approves of these treats. I added nothing to them, they were simply meat from the rump of a cow and organic. Haru says that they were very tasty and she would give me a 5 star rating! She says, All ferrets should have this healthy, delicious, meaty treat and that everyone should throw all their commercial treats away and make their own! My little girl is quite right! I agree, and if you're interested in trying to make your own freeze dried treat, feel free to check out my recipe.
Machan: I was doing some research and came across this article on the differences in cats and dogs. I thought I would share it with you since this can also apply to ferrets since like cats, ferrets are obligate carnivores which would mean that the overall body structure would be quite similar in a way. It should give you a general idea and give you some insight on general carnivore nutrition along with bits and pieces on minerals and vitamins, including even Taurine.
Article Source: http://journals.cambridge.org/downl...
Differences between cats and dogs: a nutritional view
BY VERONIQUE LEGRAND-DEFRETIN
Waltham Centrefor Pet Nutrition, Waltham-on-the-Wolds,Melton Mowbray LE14 4RT
Cats and dogs have been associated with man for many centuries, and in modern society they probably represent the two most popular companion animals. In 1992 there were approximately forty million cats and thirty-eight million dogs in Europe, representing 18 and 21% of households respectively. Despite their popularity, the nutritional require- ments of both species have only been studied in detail during the last 20 years.
Regarding zoological classification, both cats and dogs fall into the order Carnivora. However, a comparison of the nutritional requirements of the cat and the dog supports the hypothesis that specialization consistent with the evolutionary influence of a strict carnivorous diet has occurred in the cat. In addition, there appears to be more variety in the diets of Canids than in those of Felids. The ancestors of dogs are known to eat mammals, fish, birds and amphibians as well as vegetable matter (berries, apples, pears) whereas wild cats only eat animals (small antelopes, rodents, birds, fish, etc; Rohrs, 1987). Examples of the cat specializations can be summarized as follows:
The cat has limited ability to regulate the catabolic enzymes of amino acid metabolism, which causes the cat to require a higher level of dietary protein for maintenance than the dog;
The cat has a lower capacity to synthesize the sulphonic acid taurine than the dog and is unable to conjugate bile acids to glycine. Thus the cat, unlike the dog, cannot meet its taurine requirement from dietary S-containing amino acids;
The cat cannot synthesize sufficient nicotinic acid from tryptophan because of an increased activity of a-picolinic acid decarboxylase ( E C 4.1.1.45) leading to the endproduct glutamate rather than nicotinic acid;
The cat is unable to convert carotene to retinol and, therefore, cannot satisfy its vitamin A requirements with a herbivorous diet alone;
The cat cannot convert sufficient linoleic acid to meet its requirement for arachidonic acid;
The cat seems to be unable to cope with high levels of carbohydrate in its diet and appears to be in a constant state of gluconeogenesis.
These feline specificpeculiarities (which will be presented in the present paper) appear to confirm that, unlike the dog, the cat is an obligate carnivore and is dependent on a supply of at least some animal-derived materials in its diet.
PROTEIN REQUIREMENT
Total protein
Protein is required in greater amounts by the cat than most other mammals, including dogs
(Tables 1 and 2; National Research Council, 1985, 1986).
Table 1. Protein requirement (gIMJ diet) of cats and dogs
Table 2. Minimalessential amino acid requirements of kittens and puppies for growth
Work conducted at the Waltham Centre for Pet Nutrition has shown that when all essential amino acids are present at more than adequate concentrations, about 10% protein energy is required to maintain adult cats in protein (N) balance (Burger et al. 1984;Burger Sr Smith, 1987). No such studies exist in dogs. However, the National Research Council (1985) recommends that 6% of energy comes from dispensable amino acids. These studies showed that the higher protein requirement of the cat is not due to an increased requirement for essential amino acids but a need for more protein in total, irrespective of its essential amino acid content. The metabolic explanation seems to lie with the increased activity of the N-catabolizing enzymes. Alanine aminotransferase (EC 2.6.1.2) and glutamate dehy- drogenase (EC 1.4.1.3) activities are greater than those of either the dog or the rat (Table 3; Schaeffer et al. 1989). In contrast, the level of enzyme activity fix the breakdown of the essential amino acids (e.g. threonine dehydratase (EC 4.2.1.16), serine dehydratase (EC 4.2.1.13); Rogers et al. 1977) is lower in the cat than in rats fed on a high-protein diet. Finally, unlike other mammals that can adjust their rate of protein breakdown, cats seem unable to ‘switch off these mechanisms when presented with a low-protein diet (Table 4; Rogers et al. 1977).
Arginine
Table 3. Effect of dietary protein on hepatic alanine aminotransferaseactivity (EC 2.6.1.2;pmollmin per g) (From Schaeffer et al. 1989) (Mean values with their standard errors)
Table 4. Comparison of alanine aminotransferase activity (EC 2.6.1.2) in the cat and rat fed on low- and high-protein diets* (From Rogers et al. 1977)
In addition to a high total protein requirement, the cat’s requirements for a number of the individual amino acids are of particular interest. Both cats and dogs show signs of hyperammonaemia when fed on an arginine-free diet (Morris & Rogers, 1978a,b; Czarnecki & Baker, 1984). However, arginine deficiency is more severe in the cat, since a single arginine-free meal results in severe adverse effects 2-5 h later. Hyper- ammonaemia occurs following an inability to metabolize N compounds via the urea cycle, and in serious cases can lead to death (Morris & Rogers. 1978a,b). A comparison of the clinical signs in cats, dogs, ferrets and rats following consumption of an arginine-free diet led Morris (1985) to the conclusion that cats and ferrets are more sensitive to a deficiency of dietary arginine, dogs being intermediate, while growing rats exhibit only a depression in food intake.
The addition of ornithine to an arginine-free diet can prevent hyperammonaemia in kittens and puppies, although other clinical signs such as body-weight loss in kittens are not prevented (Morris & Rogers, 19788; Czarnecki & Baker, 1984). Other studies on citrulline supplementation showed that this latter intermediate of the urea cycle was not as efficiently utilized as arginine (Morris et al. 1979; Czarnecki & Baker, 1984). The susceptibility of cats to arginine-free diets seems to be related to the low activities of two enzymes involved in intestinal ornithine synthesis (pyrroline-5-carboxylate synthase (EC 1.5.1.2) and ornithine aminotransferase (EC 2.6.1.13); for further details, see Morris, 1985; Rogers & Phang, 1985). After an overnight fast, depletion of the urea-cycle intermediates occurs in the liver and in the circulation. When the cat is given an arginine-free meal, protein catabolism and amino acid deamination overload the urea cycle which is then unable to dispose of the NH3 produced. Reliance of the cat on its diet for precursors of the urea-cycle intermediates, rather than de novo synthesis, is intlicati.de of the natural animal-derived diet of the cat.
Sulplzur amino acids and taurine
No discussion of the aminoacid requirements of companion animals would be complete without mention of the importance of the S amino acids and of taurine in cats. The dietary requirement of cats for methionine and cysteine is higher than that for most other mammals, including the dog (Table 2). It was first thought that the urinary excretion in cats of felinine, a unique branched-chain amino acid, was one of the reasons for this high requirement. However, Rogers (1963) showed that 35S from [35S]methionine or [35S]cysteinewas not incorporated into felinine. Thus, if the physiological significance of felinine is territorial marking (urinary excretion of felinine is higher in adult male than in adult female cats) or involvement in the regulation of sterol metabolism, the roule of its synthesis is not known. Methionine and cysteine may act to a limited extent as precursors of taurine synthesis. However, the quantity of S amino acids needed for this synthesis does not account for their high requirement (National Research Council, 1986). Cysteine is metabolized by at least four pathways, only one of which involves the oxidation of cysteine followed by decarboxylation of cysteinesulphinate to produce taurine. The other pathways involve desulphydration of cysteine to release pyruvate, NH3 and S. The direct pathway of desulphydration accounted for 8148% of the enzyme activity in the tissue of cats fed on a high-protein diet (Park et al. 1991). The reasons for cats requiring imore S amino acids than dogs are still not explained; one suggestion is that it is related to the thick coat of the cat (MacDonaldetaf.1984).
The particular importance of taurine in cat nutrition was discovered less than 20 years ago when a taurine deficiency in cats was associated with central retinal degradation (Hayes et al. 1975). More recent research suggests that taurine deficiency is also associated with poor reproductive performance in breeding females, poor growth in kittens and dilated cardiomyopathy in adult cats (Sturman et al. 1986; Pion et al. 1987). Taurine is a p-amino sulphonic acid (2-amino ethane-sulphonic acid) and as such1is not present in protein, but its concentration in animal-derived materials is high (National Research Council, 1986). Taurine is an endproduct of S amino acid metabolism and is normally synthesized from cysteine in the liver (Fig. 1).Its main physiological sig- nificance is its conjugation with bile acids, its presence in some peptides and its role in the osmoregulation of cells. It is not metabolized as such by cat tissues since endogenous or dietary taurine is excreted in urine without modification. However, taurine can undergo microbial degradation in the gastrointestinal tract. Unlike most other animals, cats are not able to synthesize sufficient taurine to meet their needs due to a low activity of the enzymes cysteinesulphinate decarboxylase (EC4.1.1.29) and cysteine dioxygenase (EC 1.13.11.20) (Hardison et ul. 1977; Knopf et al. 1978; for review, see Morris & Rogers, 1992). However, according to current thinking, the high requirement of cats for taurine is more probably linked to bile acid enterohepatic circulation. In mammals, bile acids neosynthesized in the liver or recycled from the intestine are conjugated to glycine or taurine before being secreted into bile. Cats, unlike humans but like rats and dogs, conjugate most of their bile acids to taurine. In addition, cats and dogs, unlike rats, are unable to switch to glycoconjugation when taurine is limiting, and in taurine depletion some free bile acids appear in bile in cats (Hickman et al. 1992). Bile salts secreted into the small intestine will be mainly reabsorbed by passive and active transport in the jejunum and ileum respectively, but they might also be deconjugated and/or metabolized into secondary bile salts by intestinal bacteria. Taurine released by deconjugation may be either reabsorbed from the intestine or lost from the taurine pool. Thus, bile salt production represents an obligatory loss of taurine for the cat (Sturman et al. 1978). The cat’s requirement €ortaurine is higher when fed on a canned food than when fed on a dry food (canned food 2200-2500 mg taurine/kg dry matter; Pion et al. 1989; Earle & Smith, 1991;dry food 1000mg taurine/kg dry matter; Douglass et al. 1991). The reasons for this discrepancy have yet to be explained but one hypothesis is that the enterohepatic circulation of bile salts is increased in cats fed on canned products since, on a dry matter basis, these generally contain more fat than dry products. If this is the case, decon- jugation of bile salts by intestinal bacteria will be increased and, although some taurine is usually reabsorbed from the intestine, its excretion from the digestive tract may be augmented.
VITAMIN REQUIREMENTS
Nicotinic acid
In most animals, nicotinic acid is an endproduct of tryptophan degradation (Fig. 2). Thus, dietary requirements are dependent on the level of tryptophan in the diet. However , the efficiency of this pathway is species-dependent according to the presence andor activities of the enzymes involved in tryptophan catabolism. In cats, rate of removal of the intermediate a-amino-P-carboxymuconic-esemialdehydeis so rapid that no nicotinic acid is produced (Da Silva et al. 1952; De Castro et al. 1957; Ikeda et al. 1965). This is due to the high activity of a-picolinic carboxylase which actively transforms tryptophan into glutamic acid even after tryptophan loading (Da Silva et al. 1952). Accordingly, although dogs have historically played an important role in the understanding of the development of pellagra in humans, their requirements for nicotinic acid are smaller than those of cats (growing dog 717 p,g/MJ metabolizable energy (ME), growing cat 1912 p.g/MJ ME; Morris & Rogers, 1989).
Vitamin A
The term vitamin A correctly applies only to retinol, retinaldehyde and retinoic acid. Preformed retinol is found in foods of animal origin and some bacteria, while only small amounts of retinaldehyde and retinoic acid may occur in foods. Dehydroretinol can be reduced to retinol in vivo, has half the biological activity of retinol, and can be found as a dietary source in freshwater fish and amphibians. A number of carotenoids, called provitamin A carotenoids, are present in plants, fruits and milk. Among these compounds, f3-carotene is the most important because in most animals it has the highest vitamin A activity when transformed by intestinal carotene dioxygenase (EC 1.14.99.5) to retinaldehyde (Turner, 1934). However, the activity of this enzyme is low, so that in many species such as dogs and humans a relatively large proportion of ingested p-carotene may appear in the circulation unchanged. In cats, this situation is pushed to an extreme since this enzyme is undetectable in their intestinal mucosa (Gershoff et al. 1957). Thus, the requirement of cats for vitamin A can be fulfilled only from food of animal origin, which provides preformed vitamin A.
ESSENTIAL FATTY ACID REQUIREMENTS
Most animals have a requirement for polyunsaturated fatty acids (n-6 series) which can be satisfied by the provision of linoleic acid (18:2n-6) in the diet. Alternating steps of desaturation and chain elongation allow production of y-linolenic (18:3n-6), dihomo- y-linolenic (20:3n-6) and arachidonic acids (20:4n-6) successively (Fig. 3). Early studies on these metabolic pathways were carried out in rats and it was assumed that they were present in other animals. Rivers et al. (1975) reported low levels of plasma arachidonic acid in cats fed on purified diets containing linoleic acid but no arachidonic acid. Subsequently, Rivers et al. ( 1 9 7 6 ~ a~n)d Hassam et al. (1977) reported that cats were unable to synthesize y-linolenic acid from linoleic acid or arachidonic acid from dihomo-y-linolenic acid because of a defect in A6-desaturase and A5-desaturase activities. Frankel & Rivers (1978) then fed evening primrose oil (rich in y-linolenic acid) to cats that had previously been fed on safflower seed oil as the only source of fat. After 5 d there were increased levels of y-linolenic and dihomo-y-linolenic acids but not of arachidonic acid that led these authors to postulate a lack of A5-desaturase activity. However, after 10 weeks the level of arachidonic acid was increased (Frankel, 1980). Meanwhile, Sinclair et al. (1979) showed the ability of cats to synthesize arachidonic acid from y-linolenic and dihomo-y-linolenic acids but not from linoleic acid and concluded that A5-desaturase activity was present in the liver of the cat. In conclusion, cats, unlike dogs, have an essential requirement for arachidonic acid because of limiting A6- desaturase activity. Since arachidonic acid is present only in fat of animal origin, cats must be seen as obligate carnivores.
CARBOHYDRATE METABOLISM
Providing their diet supplies sufficient gluconeogenic amino acids and fat (thus, glycerol), cats can be maintained on a carbohydrate-free diet. In dogs, although carbohydrate can be of importance in the diets of some racing breeds (Legrand-Defretin & Munday, 1993), there is no known minimum requirement for this nutrient. However, petfoods commonly contain moderate to high levels of carbohydrate (i.e. cat foods 70-500 g/kg dry weight, dog foods 60-700 g/kg dry weight). Starch, sucrose and lactose are the main dietary carbohydrates, although lactose and sucrose, present in milk and sugar cane respectively, are less common in the diets of cats and dogs. In addition, it has been reported that both adult cats and dogs can exhibit lactose intolerance characterized by severe diarrhoea (Morris et al. 1977; Mundt & Meyer, 1989). Cats also differ from dogs in their carbohydrate metabolism since they appear to be in a constant state of gluconeogenesis. The concentration of hexokinase (EC 2.7.1.1) in the feline liver is similar to that of other omnivorous animals but glucokinase (EC 2.7.1.2) activity is lower, suggesting that cats will not be able to handle high-carbohydrate diets (Ballard, 1965). Pancreatic amylase (EC 3.2.1.1) activity is approximately three times higher in the dog than in the cat and high levels of dietary starch stimulate intestinal amylase activity to a greater extent in dogs than in cats (Meyer & Kienzle, 1991). Cats can maintain their plasma glucose levels when starved after having been fed on a high-protein diet, whereas cats previously fed on a high-carbohydrate diet showed decreased glucosaemia (Kettlehut et al. 1978). Increasing the protein level of cat rations does not stimulate the activity of phosphoenolpyruvate carboxykinase (EC 4.1.1.32), a key glucorieogenic enzyme (Kettlehut et al. 1978). The activity of another gluconeogenic enzyme, hepatic serine-pyruvate aminotransferase (EC 2.6.1.51), has been reported to be very high in cats and other carnivores (Rowsell et al. 1979). Finally, both glucagon and insulin seem to be more responsive to amino acid stimuli than to glucose (for review, see Morris & Rogers, 1989).
CONCLUSION
Although the present review of the nutritional differences between dogs and cats is not intended to be exhaustive, the examples of feline peculiarities presented here illustrate the obligate carnivorous nature of this animal. The field of carnivorous nutrition is wide and has not been extensively studied. However, it can be suggested that the cat could be used as a model to illustrate and show well-established pathways in a new light. For example, lions, like cats, are unable to desaturate linoleic acid (Rivers et al. 197tib). It is believed that the lack of adaptation of cats to changes in dietary composition is the consequence of low evolutionary pressure. Although both cats and dogs have been associated with humans for millennia, the latter have developed a dependence on humans for finding food whereas the former have kept their hunting nature. In terms of practical feeding, it seems evident that cat food should contain animal-derived raw materials to ensure that all their requirements are met.
