Page 130 - Small Animal Clinical Nutrition 5th Edition

Minerals and Vitamins 131

loquinones and menaquinones is much slower than that of not readily available. Therefore, diagnosis relies almost entirely
VetBooks.ir menadione and they are primarily excreted in feces as a glu- upon clinical signs and nutrient intake history.
B vitamins are relatively nontoxic and may be supplied to vet-
curonide conjugate.
erinarians in individual or combination forms. Because many of
Because microbially synthesized K is readily absorbed by
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passive diffusion in the colon in most mammalian species, the B-vitamin deficiencies present with overlapping clinical
dietary supplementation is unnecessary for most cats and dogs. signs, it may be prudent to treat deficiency with vitamin-B
complex. If signs are specific for a particular B-vitamin defi-
REQUIREMENTS ciency, and if the single preparation form of the vitamin is avail-
AAFCO (2007) does not have a recommended allowance for able, individual targeted treatment may be initiated. However,
vitamin K for dogs, but recommends 0.1 mg/kg DM for cats individual preparations of B vitamins are often more expensive,
when cat foods contain more than 25% fish. This recommen- and the relative nontoxic levels of B vitamins warrant treatment
dation is warranted because vitamin K deficiency has been with the combination form.
observed in cats fed certain commercial foods containing high
levels of salmon or tuna (Case 6-8). NRC (2006) recommends Thiamin
that the vitamin K allowance is 1 mg/kg DM for cats for all Thiamin or vitamin B consists of one pyrimidine ring and one
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lifestages. For dogs, the recommended allowance of vitamin K thiazole ring linked via a methylene group. Thiamin may exist
is 1.64 mg/kg DM for growth, 1.63 mg/kg DM for mainte- as free thiamin or in the mono-, di-(pyro), or triphosphate con-
nance and 1.6 mg/kg DM for gestation and lactation. figuration. Thiamin pyrophosphate (80%) is the major form
found in tissues; the other three forms are found in lesser
DEFICIENCY AND TOXICITY amounts (Rindi, 1996; Brody, 1994a). Thiamin is very labile,
Prolonged clotting times and excessive bleeding have been especially in wet foods, being susceptible to neutral and alkaline
reported in vitamin K deficiency in cats and dogs under vari- conditions, heat, oxidation and ionizing radiation.
ous conditions. Vitamin K deficiency usually occurs second-
ary to other conditions such as malabsorptive diseases FUNCTION
(inflammatory bowel disease), ingestion of coagulant antago- Thiamin pyrophosphate (TPP) is the major coenzymatic
nists (coumarin, indanedione), destruction of gut microflora form of thiamin and is required for only a small number of enzy-
by antibiotic therapy (sulfonamides and broad-spectrum matic reactions.TPP is involved in the following general scheme
antibiotics) and congenital defects (γ-glutamyl carboxylase of reactions: 1) nonoxidative decarboxylation of α-ketoacids, 2)
defect in Devon Rex breed of cats). Vitamin K (menadione) oxidative decarboxylation of α-ketoacids and 3) transketolation
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has lower lipid solubility and is the most effective form of reactions. Thiamin may also have a function unrelated to coen-
vitamin K for cases of malabsorption. Vitamin K is the only zyme activity. TPP is concentrated in neuronal cells and may
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form of vitamin K effective in anticoagulant antagonism affect chloride permeability by controlling the number of func-
(Edwards and Russell, 1987). tional channels, possibly by phosphorylation.
Phylloquinone produces no adverse effects when adminis-
tered to animals in massive doses by any route (NRC, 1987). METABOLISM
The menaquinones are similarly thought to have negligible Dietary thiamin may be present in any of the four forms
toxicity. Menadione, however, can produce fatal anemia, hyper- mentioned above or may be of synthetic origin. Whatever the
bilirubinemia and severe jaundice. The intoxicating doses form, thiamin is hydrolyzed to free thiamin by intestinal phos-
appear to be at least three orders of magnitude above those lev- phatases before absorption by enterocytes. Absorption takes
els required for normal physiologic function (Combs, 1998). place primarily in the jejunum by an active, carrier-mediated
Neither AAFCO nor NRC has set maximum or safe upper transport that also phosphorylates the vitamin. Passive diffu-
limits for dogs and cats. sion becomes an important mode of absorption when dietary
thiamin intake is high.
SOURCES Absorbed thiamin is transported in erythrocytes, which con-
Data for vitamin K content of foods are limited by the lack tain free thiamin and its phosphorylated forms, and in plasma,
of good analytical methods. Nevertheless,because dietary needs which only contains free thiamin and its monophosphate form.
for vitamin K are low, most foods contribute significantly to Tissues take up thiamin and may interconvert it between any of
those needs. Rich sources of vitamin K include alfalfa meal, its four forms. The liver, heart and kidneys have the highest
oilseed meals, liver and fish meals. Menadione sodium bisulfite concentration of thiamin.
complex and menadione dimethypyrimidinol bisulfate are
commonly used as vitamin K sources in pet food because of REQUIREMENTS
their stability during manufacturing and storage. The AAFCO (2007) recommended allowance for thiamin is
1 mg/kg DM for dogs and 5 mg/kg DM for cats, irrespective
Water-Soluble Vitamins of the lifestage. NRC (2006) recommends a thiamin allowance
Deficiency of B vitamins occurs in veterinary medicine but may for dogs of 1.38 mg/kg DM for growth and 2.25 mg/kg DM
be difficult to specifically diagnose because analytical tests are for maintenance and reproduction. For cats, the NRC (2006)