ADULT 2 (RCCI Size), MATURE Adult (Vet Size) and SENIOR 28 (Feline Nutrition) are low-phosphorous diets: Why?
In Adult 2 products, the phosphorus level is about 30 % lower than in Adult 1 products ; it is the same for the Senior 28, compared to products proposed to younger adult cats. This restriction is done in order to prevent from some potential negative effects due to phosphorus, when kidneys do not work so well.
Regulation of the phosphorus level in the blood
In a healthy animal, the kidney is able to keep the phosphorus of the blood at a constant level. If the amount of phosphorus ingested increases, the kidney normally excrete more phosphorus in the urine, in order to bring phosphorus back to its initial level. This balance is under the influence of a major hormone, the parathyroid hormone (PTH).
Consequences of an impaired renal function
In some animals, the functional capacity of the kidneys is altered by the ageing process. The blood filtration is slightly slowered, and phosphorus excretion decreases. Then, phosphorus tends to accumulate in the blood, and make the ratio calcium / phosphorus in the blood drop.
Consequently, parathyroid hormone, whose role is to keep stable the ratio calcium/phosphorus in the blood, is oversecreted. As the renal filtration is impaired, this hormone tries vainly to stimulate the phosphorus excretion. Then, to make the calcium level in the blood higher, PTH enhances the mineral mobilisation from the bone. Actually, as phosphorus is released with calcium, it worsens the situation.
Chronic oversecretion of PTH may lead to serious troubles:
- perturbation of the nutritional metabolism,
- progressive demineralization of the skeleton, hence the "rubber jaw syndrom" observed in animals suffering from serious renal deficiency.
- PTH in excess would also play an important causative role in the occuring of clinical signs of renal deficiency.
These classical signs of renal deficiency (more frequent urination, increased water intake, blood rise of urea and creatinine levels), generally develop when 75 % of the kidneys at least, become non-functional. On the contrary, negative effects of an excessive secretion of PTH can start way earlier. This is why it is very interesting to prevent from phosphorus accumulation.
Interest of a dietary phosphorus restriction
In an animal that does not show any clinical sign of renal deficiency, phosphorus restriction is considered as a preventive measure. Actually, this disease is likely to evoluate in an invisible way for years, before becoming obvious. Preventing from progressive phosphorus accumulation is a safety measure that could reasonnably help delaying the decline of the renal function.
In dogs and cats that are clinically renal deficient ones, phosphorus restriction allows to make markedly dicrease the progression of the kidney disease. Life expectancy is then improved. (Let's point out that the product Canistar S3, for clinically renal deficient dogs, contains even less phosphorus than Adult 2 products, i.e: 0,3 %). In human dietetics, dietary phosphorus restriction is systematically applied to renal deficient persons.
To be efficient, phosphorus restriction must be set up early in the course of the renal ageing process. It is why, in large breed dogs whose life expectancy is shorter than for other dogs, this dietetic measure is applied as early as the Adult 1 (RCCI Size) or Young Adult (VetSize) stage.
In general, the phosphorus content in dog and catfood exceeds their strict requirements. Then, the reduced phosphorus levels of Adult 2/Mature Adult and Senior 28 products are far from beeing likely to induce any deficiency.
NB Phosphorus is also dicreased in Persian 30, that can be advised to Persian cats whatever how old they are.
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