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  • mymorgy
    Feline Nutrition Update Vincent Biourge France Our knowledge of the nutritional needs of cats has expanded greatly over the last 30 years thanks to the work
    Message 1 of 1 , Jun 1 4:03 AM
      Feline Nutrition Update

      Vincent Biourge France

      Our knowledge of the nutritional needs of cats has expanded greatly
      over the last 30 years thanks to the work of many dedicated
      researchers and particularly the team of Prof. Q. R. Rogers and
      Prof. J. G. Morris, at the University of California, Davis. It is
      now recognized that cats require specialized diets formulated for
      their specific nutritional needs. Those specific needs are the
      result of their long history as flesh eaters that lead into
      modifications of enzyme activities and thus, nutrient metabolic


      Cats have a high protein requirement. This requirement is not
      explained by a higher amino acid requirement for protein synthesis
      but rather by their limited ability to control the activity of amino
      acid catabolic enzymes. Whatever the protein content of their diet,
      the activities of those enzymes in cats will correspond to the
      activities in dogs or humans receiving a high protein diet. This
      adaptation is beneficial to cats. It allows them to transform the
      protein that is plentiful in their natural food into glucose, an
      essential nutrient that is present only at low concentration in
      their prey.

      Fasting in obese cats has been associated with liver lipid
      accumulation that becomes pathological over a five to six week
      period and mimics Idiopathic Feline Hepatic Lipidosis. Protein
      supplementation during the fast slows down this accumulation.

      Amino acids

      Cats require the same nine essential amino acids that are needed in
      the diet of all mammals. However, cats also require arginine and
      taurine. Although cats fed a diet deficient in arginine will develop
      severe hyperammonemia and may die as a result, protein sources
      commonly used in the formulation of cat food will easily fulfill all
      the arginine requirements. Lipid accumulation observed in cats
      suffering from hepatic lipidosis does not appear linked to arginine
      deficiency or orotic acid accumulation as has been described in rats.

      Taurine is essential in the diet of cats and its deficiency results
      in a wide range of clinical signs including fetal abnormalities,
      delayed growth and development, central retinal degeneration and
      dilated cardiomyopathy. While the ability of cats to synthesize
      taurine from methionine and cystine is very limited, they are
      obligate users of taurine to conjugate with bile acids. Formation of
      bile salts results in a continual loss of taurine, as a proportion
      of the taurine is not recovered in the enterohepatic re-circulation.
      In order to provide sufficient taurine in cat foods to maintain
      plasma and blood levels in the optimal range, studies at Davis found
      that dry extruded cat foods required about 1 g/kg diet, but canned
      foods required up to 2.5 g/kg. Indeed, canned diets have been shown
      to promote a gut flora with a higher rate of taurine degradation
      than that supported on expanded diets. One may question why cats
      would have evolved with limited synthesis of a key nutrient such as
      taurine. The answer is that cats do not need to synthesize any
      taurine if they consume a diet only of animal tissue and that the
      synthesis of taurine represents a loss of potential energy to cats
      as excess taurine is excreted in the urine.


      Cats have the ability to digest and utilize high levels of fat in
      their diets. High fat, low carbohydrate diets commonly improve the
      condition of feline patients suffering chronic diarrhea and
      most "premium" diets are formulated accordingly.

      One gram of fat provides 2.25 times more calories (9 kcal/g) than 1
      g of protein or carbohydrate (4 kcal/g). Fat is thus a concentrated
      source of energy and diets that are high in fat, although well
      tolerated by the animal, may promote obesity if not strictly
      rationed. Cats being fed high fat (± 20%) premium and super-premium
      diets are two to three times more likely to become overweight. On
      the other hand, cats being fed a diet containing around 10 % fat are
      50 % less likely to be overweight. A recent study at the Veterinary
      School of Nantes confirmed those observations; neutered cats fed a
      20 % fat dry food, gained more weight and accumulated significantly
      more body fat than control cats fed an otherwise similar 10 % fat

      Most cat owners tend to feed their animals free choice. A common
      belief is that cats are better than dogs at maintaining their body
      condition. The latest epidemiological studies no longer support this
      idea. If cats are offered a highly palatable, high fat, diet-free
      choice, they tend to overeat, especially if they are neutered.
      Although the prevalence of neutered cats presented to veterinarians
      ranges from 75 to 95 % depending on the country, a survey of 500
      practitioners showed that while most of them were aware of the
      weight-gain predisposition of sterilized cats, only 10 % of them
      advised owners to reduce the fat content of diets fed to their
      neutered pet.

      Essential fatty acids

      All mammals require a diet that contains at least one essential
      fatty acid that they cannot synthesize de novo: linoleic acid from
      the omega-6 family. The essentiality of alpha-linolenic acid (omega-
      3 family) remains controversial in dogs and cats. While cats can
      elongate these fatty acids, their ability to desaturate them,
      particularly to produce arachidonate from linoleate is limited.
      Therefore, cats also need arachidonic acid in their diet. Diets
      deficient in arachidonic acid will induce in cats poor reproductive
      performances and insufficient platelet aggregation. The only
      practical dietary source of arachidonate has been animal fats and
      tissues particularly fatty acids from membranes. This is one of the
      reasons why people should be discouraged from offering exclusively
      vegetarian diets to cats.

      There has been considerable recent interest in whether there is an
      optimal ratio of n-3 to n-6 fatty acids in the diet of normal cats.
      Eicosanoids derived from the n-6 fatty acids tend to be pro-
      inflammatory, whereas those derived from the n-3 fatty acids less
      so, or anti-inflammatory. In inflammatory conditions, it has been
      suggested that n-3 to n-6 fatty acid ratio should be increased but
      there has not been a clear definition of what is an optimal ratio
      for all physiological functions. Fish oil, richer in long-chains n-3
      fatty acids would be a better source than vegetable oil such as
      linseed oil.


      Although a diet of animal tissues contains very little
      carbohydrates, the cat is quite capable of digesting and
      assimilating sugars and starches present in foods. Thus while the
      cat appears to have evolved as a strict carnivorous, there is no
      nutritional basis for precluding a portion of the energy in the diet
      being supplied from carbohydrates, provided needs for all other
      nutrients are met. However, limited amylase activity in the pancreas
      and the small intestine of cats compared to dogs, may explain why
      some sensitive cats will not always tolerate high starch diets and
      why those individuals do better on higher fat diets.

      Dietary fibers

      Although not usually found in the natural diet of cats, dietary
      fibers are commonly present in commercial foods, mainly in expanded
      diets but also in some canned food. Dietary fibers have been shown
      in many species to have an important role on intestinal transit
      time, to balance the microflora and for the nutrition and health of
      the colon. Dietary fibers also play an important role on fecal
      volume and appearance. Fecal moisture is very much linked to fiber
      source; therefore, source of soluble fibers (beet pulp, soy fiber,
      oat bran, psyllium) might be of benefits in the prevention and
      treatment of constipation. Higher levels of fibers are recommended
      to reduce the energy content of the diet but will promote bulky
      feces. Insufficient fiber content will result in poorly formed and
      odorous feces.

      Minerals and urinary calculi

      Diet formulation, amount and balance of mineral elements in the food
      have marked effect on the formation of urinary calculi. The two most
      common calculi that occur in cats are struvite and calcium oxalate
      calculi. Before the 90's, struvite (MgNH4PO4·6H20) uroliths were the
      most common causes of lower urinary tract diseases in cats. An
      alkaline urinary pH and high dietary magnesium are generally
      considered the most important factors in their formation. Urine pH
      is much more important, however, and struvite crystals formation is
      not possible at pH below 6.5. The ability of a diet to induce acidic
      urine depends on the ingredients used and the addition of acidifiers
      such as methionine, ammonium chloride and phosphoric acid. Animal
      proteins, corn gluten and digests promote acidic urine while most
      vegetable proteins and some mineral salts such as calcium carbonate
      promote alkaline urine. Urine acidification is not without potential
      toxicity. Excessive acid load can overwhelm the ability of the
      kidney to excrete protons and induce uncompensated metabolic
      acidosis. Chronic acidosis in cats increases urinary potassium
      losses, and could potentially slow growth, increase urine calcium
      excretion and promote bone demineralization. Acidifiers have
      toxicity on their own. Acidifying diets that have been tested are
      thus the safest way to prevent and manage struvite-related LUTD.
      Today, many commercial cat foods are formulated to induce acidic
      urine even if they are not marketed as acidifying diets. Acidifying
      diets are not recommended for kittens since they may interfere with
      bone formation. Acidifying diets might also not be ideal in older
      cats (> 10 years) since these animals are at higher risk for calcium
      oxalate uroliths and renal disease. Healthy kidneys are essential
      for proton excretion.

      In the last 15 years, the proportion of uroliths analyzed at the
      University of Minnesota Urolith Center and composed of struvite has
      steadily decreased whereas the percentage of calcium oxalate has
      increased. Although it has not been proven, this observation is
      attributed to the widespread use of acidifying diets that, aside
      from unmasking other causes of LUTD, could theoretically promote
      calcium oxalate crystals formation in sensitive animals. The
      pathophysiology of calcium oxalate crystal formation in cats is not
      understood and deserves further studies. Factors known in human
      beings and laboratory animals to stimulate their formation include:
      urine pH below 7.0, increased urinary calcium, oxalate and urate
      excretions, decreased urinary magnesium and citrate concentrations,
      and abnormalities or absence in proteins known to inhibit crystal
      formation. Calcium oxalate develops in older cats than those that
      develop struvite. No diet will promote the dissolution of calcium
      oxalate uroliths but based on the current knowledge and in order to
      minimize the risk of crystal formation, diets for mature and older
      cats should be formulated to induce higher urinary pH.

      The current recommendation is to avoid high dietary NaCl in feline
      acidifying diets to minimize urinary Ca excretion and therefore
      urinary Ca oxalate (CaOx) saturation. Recent studies in our
      laboratory, comparing commercial diets or diets differing only by
      their NaCl content, concluded that higher dietary NaCl intake
      increases urine output, which is beneficial against all forms of
      urolithiasis, and was not associated with increased CaOx saturation.
      This observation suggests that moderate increase of dietary NaCl
      might be of benefits in acidifying diets.


      Vitamin A

      It has long been appreciated that cats are unable to use the ß-
      carotene from plants as a source of vitamin A. Cats lack the enzymes
      required to cleave the carotene molecule to retinal. A continual
      diet of liver has been reported to produce skeletal changes such as
      exostoses of the spine in cats in countries such as Australia and
      Argentina where livers are from cattle grazing on pasture before
      slaughter. Liver is commonly used to produce digests or as an
      ingredient in cat foods explaining the high levels of vitamin A that
      are observed in some commercial foods. Studies designed to evaluate
      if high levels of vitamin A could be associated with health problems
      in queens showed that cats were quite resistant to vitamin A

      Vitamin D

      For most animals, vitamin D is a conditional nutrient in the diet in
      that it is only when that animal does not receive exposure to
      sunlight that it becomes an essential nutrient. Dr J.G. Morris
      recently demonstrated the inability of kittens to synthesize vitamin
      D when exposed to sunlight or UV light. The explanation is that the
      7-dihydrocholesterol (the precursor for vitamin D synthesis) is in
      very low concentration in cat skin. In the wild state cats, obtain
      sufficient vitamin D from prey. Although we know now that vitamin D
      is an essential nutriment in cats, the dietary levels already
      recommended in commercial foods will fulfill all their requirements.


      As cats evolved eating a strict carnivorous (meat) diet, many of the
      enzymes required for the synthesis of nutrients present in meat (but
      not in omnivorous diets) became redundant. The activities of these
      enzymes have declined, as maintenance of redundant enzymes is an
      unnecessary energy cost for cats. Examples of such enzymes include
      those involved in the synthesis of arginine, EFA, and vitamin A. For
      other nutrients, the activities of enzymes remain elevated (high
      protein requirement) and result in substrates not being available
      for synthesis (vitamin D), or produce a change in the flux along a
      pathway away from nutrient synthesis (niacin, taurine). These
      enzymatic modifications presumably served cats well until very
      recent times when cats could no longer meet their nutritional needs
      from predation but had to rely on the consumption of foods that do
      not always contain the nutritional profile of prey.

      Formulation of commercial cat food must take those peculiarities
      into account in order to fulfill the dietary requirements of cats,
      promote health and minimize the risks of deficiencies. As some
      diseases such as obesity, hepatic lipidosis, or lower urinary tract
      diseases have been associated to the diet in cats, formulation
      should be adapted to the most up-to date information in order to
      minimize their occurrence. Pet owners should also be correctly
      advised on how to feed these diets (e.g., free-choice or limited
      intake) for their particular animal (e.g., younger vs. older cats).

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