Page 113 - Small Animal Clinical Nutrition 5th Edition

114 Small Animal Clinical Nutrition

Box 6-3. Calcium-Phosphorus Ratios.
VetBooks.ir The “ideal” calcium-phosphorus ratio recommended for animals containing calcium-phosphorus ratios as low as 0.65:1 to kittens

with simple stomachs is generally considered to be between 1:1
and 2:1. A number of factors, however, influence the importance of and found no adverse effects, provided dry matter calcium and
phosphorus levels exceeded 0.5 and 0.63%, respectively. Morris
this ratio. Increasing levels of vitamin D reduce the significance of and Earle determined these calcium and phosphorus levels to be
adverse calcium-phosphorus ratios. Furthermore, the ratio can dif- the calcium and phosphorus requirements for kittens. Results
fer markedly with the form and availability of the calcium and phos- showed that this ratio (0.65:1) was well tolerated by kittens. Feed
phorus supplied in the diet. For example, animals eating foods high consumption, body weight gain, hematologic parameters and con-
in phytate phosphorus require greater phosphorus intake to meet centrations of plasma total and ionized calcium, total phosphorus,
their needs. Thus, the ideal calcium-phosphorus ratio would be alkaline phosphatase, PTH, creatine phosphokinase, total plasma
lower when foods with these dietary characteristics are fed vs. protein and albumin and plasma 25-OH-D did not differ from val-
foods composed of mostly meat ingredients. ues in kittens fed foods with higher calcium-phosphorus ratios.
Investigators sometimes debate whether the calcium-phospho- Investigators noted significant changes in ionizable calcium con-
rus ratio is more important than absolute calcium and phosphorus centrations; however, at 18 weeks in kittens fed foods with a cal-
levels (Table 1). For all practical purposes, however, if a food were cium-phosphorus ratio of 0.38. These studies indicate that cats
formulated to meet or slightly exceed an animal’s requirement for may tolerate wider dietary calcium-phosphorus ratios than the pre-
calcium and phosphorus, it would by default provide an optimal viously recommended ratios between 1:1 and 2:1.
calcium-phosphorus ratio. The more rapid the growth rate (e.g.,
large- and giant-breed puppies >small-breed puppies >adult The Bibliography for Box 6-3 can be found at
dogs), the more critical it is to optimize calcium and phosphorus www.markmorris.org
levels (Chapter 33). Increasing energy density increases the calci-
um and phosphorus requirement; the younger the animal the more Table 1. Examples of calcium-phosphorus percentages and ratios.
critical it is that calcium and phosphorus be optimal.
% calcium/% phosphorus
Calcium-phosphorus ratios less than one have been evaluated Examples (calcium-phosphorus ratio)
in cats. Kealy et al compared the effects of feeding two foods with
different calcium-phosphorus ratios to adult cats for 52 weeks. AAFCO adult allowance for 0.6/0.5 (1.2:1)
(The foods had 1:1 vs. 0.6:1 ratios; dry matter calcium and phos- calcium and phosphorus in dogs
AAFCO growth allowance for 1.0/0.8 (1.25:1)
phorus levels were 1.27% calcium, 1.29% phosphorus and 0.75%
calcium and phosphorus in dogs
calcium and 1.24% phosphorus, respectively.) Serum concentra- Example of why tuna is a poor 0.157/1.28 (0.12:1)
tions of total calcium, ionized calcium, phosphorus, PTH, alkaline source of calcium and has a
phosphatase and vitamin D analogs did not differ between cats fed poor calcium-phosphorus ratio
Example of a correct ratio, but 2/1.6 (1.2:1)
the two different foods at any sampling time and no signs of ortho-
excessive calcium and
pedic diseases or bone loss developed during the study. phosphorus levels
Likewise, Morris and Earle evaluated the effects of feeding foods

Phosphorus requires the coordinated efforts of the kidneys and intestine.
Phosphorus is a vital participant in a number of tissues and Under conditions of low dietary phosphorus intake, the intes-
functions. After calcium, phosphorus is the second largest con- tine increases its absorptive efficiency to maximize phosphorus
stituent of bone and teeth. Phosphorus is a structural compo- absorption and the kidneys increase renal phosphorus transport
nent of RNA and DNA, high-energy phosphate compounds or minimize urinary phosphorus losses. Hormonally, these
such as ATP and cell membranes composed largely of phos- adaptations result from changes in plasma levels of 1,25-
pholipids. As a component of nucleic acids, high-energy phos- (OH) -D and PTH. Conversely, under conditions of dietary
3
2
phate compounds and cell membranes, phosphorus is essential excess, the kidneys increase excretion of minerals. Table 6-1
in cell growth and differentiation, energy use and transfer, fatty describes effects of deficiency and excess. Avoiding excess
acid transport and amino acid and protein formation. dietary phosphorus slows progression of kidney disease
About 60 to 70% of phosphorus is absorbed from a typical (Chapter 37).
diet (Allen and Wood, 1994). In general, phosphorus availabil- There are few data to make a phosphorus recommendation;
ity is greater from animal-based ingredients than from plant- however, the most recent NRC (2006) suggests 1.0 and 0.30%
based ingredients. Phosphorus in meat is found mainly in the DM for puppies and adult dogs, respectively.
organic form, whereas in plants, phosphorus is in the form of Similar to the study design for calcium, investigators evaluat-
phytic acid. Phytate phosphorus is only about one-third avail- ed the minimum phosphorus requirement for adult cats
able to monogastric animals but availability from different (Pastoor et al, 1995). Four levels of phosphorus (provided as
grains can vary markedly (McDowell, 1992). Intestinal phos- NaH PO •2H O) ranging from 0.3 to 1.8% DM were evalu-
4
2
2
phorus absorption represents the sum of a saturable, carrier- ated. The minimum level evaluated (0.3% DM phosphorus)
mediated component and a nonsaturable, concentration- resulted in positive mineral balance with no adverse effect on
dependent component. Regulation of total body phosphorus serum phosphorus, calcium, magnesium and alkaline phos-