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Calcium:Phosphorus Ratio (Ca:P)
in Powdered Milk Replacers
Calcium and Phosphorus are closely associated with each other within animal metabolism. Adequate Ca and P nutrition depends on three factors: a sufficient supply of each nutrient, a suitable ratio between them, and the presence of vitamin D. These factors are interrelated. Much of the literature and research study is based on livestock and companion animals and has concluded that the desirable Ca:P ratio is generally in the range of between 1:1 and 2:1. Wildlife rehabilitation literature suggests a Ca:P ratio of 1.3:1 or greater, which would fall in this same range.
Since vitamin D is essential for calcium utilization, inadequacies in vitamin D will imbalance the available Ca:P ratio.
As Robert Murnane writes in the chapter "Common Nutritional Disorders of Wildlife" from the NWRA Principles of Wildlife Rehabilitation, 2 ed.,
"Metabolic bone disease is the most common nutritional disease encountered at [the University of Illinois College of Veterinary Medicine]. The etiology of metabolic bone disease involves calcium, phosphorus and vitamin D imbalance and multiple organ systems including the endocrine (thyroid and parathyroid glands and hypothalmus), skeletal (bone), gastrointestinal (intestines and liver), urinary (kidneys), integumentary (skin) vascular (plasma), and nervous (brain control of the hypothalamus) sysytems. This complex interaction results in patients with an array of clinical signs. The numerous synonyms applied to the disease (rickets, osteomalacia, fibrous osteodystrophy, nutritional bone disease) often result in confusion. All species and ages are susceptible to the disease since calcium is critical for normal function of all cells and its levels are intricately controlled." He further states... "Metabolic bone disease most often occurs due to an absolute or relative dietary calcium deficiency.
An absolute dietary calcium deficiency is a diet that does not contain adequate calcium.
A diet with relative calcium deficiency contains adequate calcium but too much phosphorus, which renders the calcium unavailable to the animal."
As Dr. Murnane suggests, diagnosing metabolic bone disease is difficult and "confusing." Even though adverse bone symptoms may develop in a wildlife patient, jumping to a quick conclusion about MBD can be detrimental. It could lead to a misdiagnosis, incorrect treatment, or cause one to overlook other underlying medical issue(s). As described above, MBD may not be related to calcium levels, but instead to an imbalance in phosphorus or vitamin D (or both), other minerals, or one or more other subtle medical conditions.
Milk replacer analysis
The Ca:P ratios are shown in the chart below for each of the two primary milk replacer manufacturers used by rehabilitators. The data spans 10+ years and shows that ALL the lots tested fell within in the acceptable range of 1:1 to 2:1. In most samples tested, the ratios fall within a tighter band of Ca:P ratio of 1.25:1 to 1:75:1. Since the correct Ca:P ratio values for all species (and ages) are likely different and largely unknown (and wild species milk composition is limited), reference values for whole and lowfat dry milk are provided in the chart for comparison.
The individual concentrations of calcium and phosphorus, and trends over time, are discussed on their respective pages in this website. Vitamin D was not included in the requested lab testing, so individual lot values for that vitamin are not reported. It is noted that all products indicate on the product labeling that Vitamin D3 supplement is included.
References and further reading (not intended as an exhaustive list)
Murnane, Robert D. Common Nutritional Disorders of Wildlife. Chapter 7, General Nutrition, NWRA Principles of Wildlife Rehabilitation, 2 ed., Moore and Joosten, eds., 2002. National Wildlife Rehabilitators Association, St. Cloud, MN.
The information included on this website for dietary minerals is extremely narrow in its scope and nature. It is limited to certain charts and graphs displaying content values (% of total) of various powdered milk replacers as tested by an independent chemical lab. Extremely brief overview information is provided as to the primary nutritional and medical benefits of each mineral, as well as a limited discussion of issues that may arise from concentration levels in the body that may be considered deficit or toxic. Entire textbooks on dietary minerals are written for the medical and veterinary professions, in addition to the internet providing ready access to both scholarly and popular literature. Some of those references are included above.
The data values presented above only represent the test values for the presence and concentration of the mineral conducted according to standard chemical testing methods in a controlled laboratory setting. Any point test value is accompanied by a measurement uncertainty range of +/-20%. The concentration values are in no measure an indication of how much of the mineral may be provided to an animal in reconstituted formula or its bioavailability (its degree of digestibility, absorption, or ultimate utilization). Additionally, no testing was performed as to the source of the mineral in the product (such as inorganic salts) or the grade of any added supplements containing the mineral.
What the data can do is inform the reader as to (1) concentration levels in a product as most recently tested (2) changes over time and between lots, and (3) comparisons of relative concentration levels between products. It is merely data that may serve as a starting point when deciding on a milk replacer product(s) and a recipe, or information to consider if certain medical symptoms appear that could be a result of absence or excess of a specific mineral in the formula. The reader is encouraged to consult veterinary or nutritional professionals prior to providing additional supplementation of any mineral.