Royal Canin Nutritional Information

7. Nutritional Information

Focus on: Sodium

After calcium and potassium, sodium is the most abundant ion in the body. It accounts for around 0.13% of the body weight of a mammal. Extracellular sodium is found in the skeleton (43% of total sodium), interstitial fluids (29%) and plasma (12%). The remaining sodium is mainly found inside the cells.

Sodium plays several essential roles in cell function:

• It maintains the osmotic pressure balance between the intra- and extracellular environment and regulates the volume of extracellular fluids. As a water balance regulator it has an important role in the development of thirst and urine elimination;
• It intervenes in acid-base balance;
• It participates in the transmission of nerve impulses.

The digestive absorption of sodium is general very important. A constant sodium level is maintained in the body by regulating renal and intestinal secretion.

When it comes to determining the salt content in different foods, it is important to measure carefully.

Publications dealing with the influence of sodium (Na) on the physiology do not always express the sodium concentration of foods in the same way. Before interpreting the results, it is advisable to distinguish the values in:
- mg or mmol of Na per kg of weight
- mg or mmol of Na per kg of food
- % of dry matter of the food.

The sodium values are sometimes given through the quantity of sodium chloride (NaCl) added. The units must therefore be taken into account before comparing values.

Calculating the equivalences between mg and mmol of sodium.

• The molecular weight of NaCl is 58.45 g/mol.
• In 1 Mole of NaCl, the sodium ions weigh 23 g and the chloride ions weigh 35.45 g.
• In 1 mmol of NaCl, the sodium ions weigh 23 mg and the chloride ions weigh 35.45 mg.
• A factor of 23 is therefore used for conversion.

Example 1:
10 mmol of sodium is equivalent to: 23 x 10 = 230 mg of Na

Example 2:
10 mg of sodium is equivalent to: 10 / 23 = 0.43 mmol of Na

Do not confuse the sodium chloride (NaCl) and sodium (Na) contents in a food.

• In 1 mole of NaCl, the sodium ions account for 39.3% of the total and the chloride ions around 60.7%.
• A factor of 0.393 is used for conversion.

Example:
1% of sodium in a food corresponds to: 1/0.393 < 2.54% of NaCl.

When the sodium source is another sodium salt, the calculation is done in the same way, based on the percentage of sodium in each salt:
- Sodium carbonate contains 37% of sodium.
- Sodium bicarbonate contains 27% of sodium.
- Sodium phosphate contains 16% of sodium.

Cats do not sweat, so they are not exposed to major losses caused by sweating, even in the event of intense effort or high temperatures.

The Dissolution Kinetics Of Feline Struvite Stones In Urine In Vitro Depends On The Urine Struvite Relative Supersaturation

Tournier C, Malandain E, Abouhafs S, Aladenise S, Venet C, Ecochard C, Sergheraert R, Biourge V. Royal Canin Research Center, Aimargues, France

Introduction

Relative supersaturation (RSS) is a method that enables measurement of the potential for crystals to form or dissolve in urine, based on composition (Figure 1). This technique has been validated in cats (Robertson et al, 2002). The aim of this study was to assess whether struvite RSS is a good predictor of the in vitro struvite (ammonium magnesium phosphate) dissolution kinetics in cat urine.

Figure 1. Evaluation of the probability of struvite stone formation based on urine saturation.

Materials and Methods

Animals and Diets

Three commercial complete dry expanded diets (A, B, C) were fed successively to 7 Chartreux cats (4 neutered males, 3 females, 6.0 ± 2.8 yrs, 5.9 ± 1.3 kg) for 2 weeks. Diets B and C were specifically formulated to dissolve struvite uroliths (low urine acid pH and RSS).

Parameters

Urinary volume, pH, specific gravity and concentrations of 10 solutes (Ca, Mg, Na, K, NH4+, phosphate, citrate, sulfate, oxalate, uric acid) were measured in pooled urine for each diet collected during the last 7 days of each study period (Table 1). Based on these data, the RSS for struvite was calculated using the SUPERSATtm software (Robertson et al, 2002).

Selection of Struvite Stones and Preparation of Urine Samples

Three groups of feline struvite stones were selected on the basis of homogeneity of shape and weight (mean weight: 0.201 ± 0.010 g). For each diet, the pooled urine from all 7 cats was aliquoted in bottles, based on the mean daily volume of urine produced by the cats. The bottles were stored at -20°C pending the study.

In vitro Dissolution Procedure

On day 0 and for each diet, a bottle of urine was defrosted and one group of struvite stones was placed in the urine (Figure 2a). The bottle was then placed in a water bath at 38°C for 24 hours (with a shaking mode during 9 hours to simulate cat activity) (2b). At the end of the 24 hour period, the urine was filtered to collect the stones (2c). The stones were lightly dried on absorbent paper (2d) and weighed (2e). A new urine bottle was then defrosted and the process repeated until complete dissolution of the stones was achieved (Figure 3).

Figure 2. In vitro struvite stone dissolution protocol.

Figure 3. Appearance of struvite stones during dissolution.

Discussion and Conclusion

With saturated urine (diet A - RSS = 7.3), little dissolution was observed over the duration of the study (Figure 4) possibly due to the abrasion of the stones during agitation.

When the RSS is < 1 (undersaturation zone), urine dissolves struvite stones efficiently (Figure 4) and the lower the RSS, the faster the dissolution kinetics (Table 2). RSS is thus a good predictor of the potential of urine to dissolve struvite.

Figure 4. Dissolution kinetics of struvite stones for each diet.