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The Journal of Nutrition Vol. 128 No. 12 December 1998,
pp. 2581S-2583S
Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA 95616 USA
KEY WORDS: cat · plasma · taurine · white blood cell · platelet
The initial association of feline central retinal degeneration with low plasma taurine concentration led to the establishment of taurine as an essential nutrient in cats and to recognition of the usefulness of blood taurine measurement in determining dietary taurine requirement in cats.
Research has since shown with plasma and whole-blood taurine measurements that dietary factors, including heat treatment, protein source, and protein concentration affect the need for taurine in the diet of cats (Morris et al. 1994 Materials and methods.
Thirty female and 30 male specific-pathogen-free kittens, 10-12 wk in age, were randomly assigned to 10 groups of six cats each, in a 5 × 2 randomized block design. All kittens originated and were housed in the Nutrition and Pet Care Center at the Davis campus of the University of California. As determined by the Animal Use and Care Administrative Advisory Committee, the husbandry and treatment of the kittens was in compliance with the Animal Welfare Act and the NIH guidelines (NRC 1996). The kittens received continuously a purified diet containing either a high (23 g/kg) or adequate (6 g/kg) level of calcium (NRC 1986) and one of five levels of magnesium (100, 200, 300, 400 and 500 mg/kg) of which 400 mg/kg was considered adequate (NRC 1986). The diet also contained (g/kg) lactic casein (New Zealand Milk Products, Santa Rosa, CA), 222.5; lactalbumin (New Zealand Milk Products), 222.5; animal tallow (Florin Tallow, Dixon, CA), 300; cornstarch (Westco Products, Sacramento, CA), 145-192; mineral mixture, 48; vitamin mixture (Hoffman-La Roche, Nutley, NJ), 10; taurine (Taisho Pharm, Torrance, CA), 1.5; and choline chloride (Dupont, Highland, IL), 3. Magnesium sulfate and calcium carbonate were added in place of cornstarch so as to adjust dietary magnesium and calcium concentrations to required levels. The mineral mixture contained (g/kg diet) CaHPO4, 19.60; K2HPO4, 4.52; KCl, 12.82; NaHCO3, 5.02; NaCl, 5.03; MnSO4H2O, 0.192; ferric citrate, 0.504; NaF, 0.0072; Ca5(IO6)2, 0.00384; ZnSO47H2O, 0.2208; CuSO45H2O, 0.0384; SnCl22H2O, 0.0048; Na2SeO3, 0.00144; (NH4)6Mo7O244H2O, 0.00192; CrCl36H2O, 0.0144; NiCl26H2O, 0.0144; and NH4VO3, 0.001.
Results.
With the exception of lower plasma taurine concentrations in cats from the group given the high calcium-200 mg/kg magnesium diet, plasma taurine concentrations among cats of all groups were not significantly different from those observed in cats receiving a diet with adequate calcium and magnesium, 6 g/kg and 400 mg/kg, respectively (Fig. 1). The variance in mean concentrations of taurine in whole blood was greater than that for plasma. The whole-blood taurine concentrations in cats given the two high calcium-low magnesium diets (100 and 200 mg/kg) were substantially greater than those in cats that received all diets with adequate calcium and the diets that were high in calcium but contained 300, 400 or 500 mg/kg magnesium.
Discussion.
Although the dietary taurine concentration was held constant, blood taurine concentrations varied significantly with dietary magnesium concentration when dietary calcium was present at 23 g/kg. Whole-blood taurine concentration was increased by a dietary magnesium concentration of <300 mg/kg (Fig. 1). As indicted by the regressions of whole-blood taurine concentration on leukocyte and platelet counts (Fig. 2), the increase in whole-blood taurine concentration resulted from increased numbers of these taurine-rich cells. The leukocytosis and thrombocytosis appeared to be a consequence of hemopoietic stimulation because myeloid and erythroid hyperplasia of bone marrow was found on histopathologic examination of the cat that was necropsied. Rats given a magnesium-deficient diet exhibited hypercellular bone marrows with marked increases in granulocytic cells and some increases in eythrocytic cells (McCreary et al. 1967
INTRODUCTION
Introduction
References
). For those dietary factors found to have an effect, a decrease rather than an increase in blood taurine concentration is typically observed. However, exceptions to this may occur. The consumption of a diet deficient in magnesium substantially elevated the serum taurine concentrations of rats (Robeson et al. 1980). It was suggested that this effect resulted from stimulation of taurine synthesis from sulfur amino acids or inorganic sulfate. The present research was prompted by this finding and was undertaken with the objectives of determining whether dietary magnesium affects blood taurine concentration in cats and, if so, the nature of the cause.
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Fig 1.
Plasma and whole-blood taurine concentrations in kittens given a purified diet with different magnesium and calcium concentrations. Values represent means ± SEM calculated from taurine concentrations of six cats, or five cats in the case of means from the group of kittens that received the high calcium-100 mg/kg magnesium diet. Mean whole-blood taurine concentrations marked with an asterisk are greater (P < 0.05) than those not marked.
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Table 1.
Estimate of the distribution of taurine in the plasma and cellular fractions of whole blood in cats given a purified diet
with 6 g/kg calcium and 400 mg/kg magnesium
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Fig 2.
Influence of blood leukocyte and platelet counts on the whole-blood taurine concentration of kittens. Plotted points with overlaying + and × symbols represent observations from kittens given a diet high in calcium that contained either 100 or 200 mg/kg magnesium, respectively.
and the mean packed cell volume, total and differential blood cell counts, and taurine concentrations found in cats given the diet with adequate calcium and 400 mg/kg magnesium (Table 1). Results of the estimate indicted that, although erythrocytes were by far the most abundant cell type, leukocytes and platelets contained most of the taurine in the cellular fraction of whole blood.
). Because generalized stimulation of bone marrow is a normal response to anemia, the presently observed leukocytosis and thrombocytosis may have been a consequence of increased demand for erythrocytes imparted by magnesium deficiency. A marked reduction in erythrocyte survival time such as that observed in magnesium-deficient rats (Heaton et al. 1987) could have driven a generalized hemopoietic response. Alternatively, increased leukocyte and platelet production may have been stimulated by activity of inflammatory cells affected by magnesium deficiency. Weglicki et al. (1992) reported that circulating concentrations of inflammatory cytokines are elevated in magnesium deficiency.
), the adequate calcium diets probably allowed absorption of enough magnesium to prevent occurrence of symptoms of magnesium deficiency. The basis for the low plasma taurine concentration observed in cats given the high calcium and 200 mg/kg magnesium diet is not readily apparent. Depression of food intake, a symptom of magnesium deficiency, was observed in some of these cats. Because plasma taurine concentration may change acutely with the intake of food, cats from this group may have consumed less diet than cats in the other groups immediately before collection of blood samples.
). Because pneumonia is often observed in animals with chest deformities, high leukocyte counts may explain the finding.
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LITERATURE CITED |
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Introduction
References
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