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Calcium and Phosphorus in the Horses Diet
Calcium, Phosphorous, and Vitamin D as Nutrients for Horses
Introduction
Calcium and phosphorous comprise 70% of the body's minerals, 40% of the minerals in milk. The vast majority is tied up in the bones. Though everyone knows that calcium and phosphorous are important for bones they are also critical in many of the body's biochemical reactions. Phosphorous is critical for energy and necessary as a ph. buffer. Calcium is essential for nerve conduction, muscle contraction, clotting, temperature regulation, glandular activity and dozens of other functions. When discussing the dietary needs of these two minerals not only is the absolute amount important but also the ratio of the two minerals must fall within certain limits for optimal health and to prevent disease. No discussion on calcium and phosphorous would be complete without discussing vitamin D. This article discusses requirements, sources, and diseases caused by excess and deficiencies of these two closely interrelated minerals.
Requirements
Calcium
NRC Calcium and Phosphorous Requirements: |
||
| Type of horse or stage of life | % cal | % phos |
| Mature and Idle (Maintenance) | 0.30 | 0.20 |
| Pregnant (last 90 days) | 0.50 | 0.40 |
| Lactation | 0.60 | 0.40 |
| Weanling | 0.70 | 0.40 |
|
Light to medium work
(these numbers may be low, see text for more) |
0.35 | 0.25 |
Phosphorus
Requirements posted in the table for horses at maintenance, growing, horses, pregnant and lactating mares are reasonable. The effects of long-term feeding of various levels of phosphorus on bone integrity needs further study.
Vitamin D
The only known function of vitamin D is to regulate calcium and phosphorous concentrations in the blood. However it has been shown to inhibit the proliferation of and promote differentiation of many cell lines and as such has been used in certain hyperproliferative disorders. Levels of 6 (maintenance) to 24 IU (growth) per kg of bodyweight. Any horse that receives either several hours exposure to daylight a day or sun cured forage that has been stored less than 6 months will receive an abundance of vit D. In the horse, deficiency of vitamin D has never been observed though attempts to induce it experimentally have been made. Vitamin D toxicosis is the most common toxicity caused by vitamins and caused by formulation errors, excessive administration or the ingestion of vitamin D accumulating plants.
Does Vigorous Exercise Change Needs?
More studies need to be conducted on the effect of the calcium intake on bone integrity. There is concern about the calcium requirements for young horses in training:
- bone density began to decrease at the onset of training and continued to do so until day 62 of training, remaining low through day 104 when it began to increase to day 224.
- Horses with greater bone (cortical) mass had fewer injuries.
- In a subsequent study, it was demonstrated in balance studies that horses in typical race training at 24 months of age retained 4 to 6 more grams of calcium per day when fed 36 g of calcium per day, than when 30 g of calcium were fed per day.
Amount in Common Feedstuffs
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