Importance of calcium and phosphorus in the ruminant diet

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Calcium (Ca) and phosphorus (P) are two of the most abundant minerals in the body, which is why they are vital to the discussion of feed testing and ration balancing for cattle. The importance of these minerals and the role they play in the body can help ranchers understand why a balanced mineral program is a notch in the key to success.

Due to the abundance of these minerals in the body, it is important to understand the function and how to meet requirements to insure that deficiencies and toxicities are not a concern. The main function of both calcium and phosphorus is skeletal. Nearly 99% of the calcium in the body if found in the skeleton, while 80% of the phosphorus is in bones and teeth. The remaining Ca is extracellular and plays a role in nerve conduction, muscle contraction, blood clotting and immune system activation. The remaining P is involved in energy utilization and transfer, acid-base and osmotic balance, and for cattle is required by ruminal microbes for growth and cellular metabolism.

Rarely is there a need to be concerned with toxicity of Ca or P in the diet; however deficiencies can occur at different times throughout the production cycle of cows, depending on the feed source. In general, forages provide adequate amounts of Ca in the diet, especially if there are legumes in the mix. Times when we are most likely to see a Ca deficiency is shortly after calving when the cow’s Ca loss due to lactation exceeds Ca entry. Depending on time of year, this can be exacerbated due to low Ca levels in forage. Low diet Ca will lead to Ca being taken from the bone reserve. This is commonly referred to as milk fever or tetany. If suspected, consult a veterinarian.

In growing cattle diets it becomes even more critical to test feeds and balance minerals accordingly, as they have a higher requirement for Ca and concentrate feeds typically used in backgrounding or finishing are lower in Ca than forages.

On the other hand, phosphorus deficiency is the most prevalent deficiency throughout the world, as forages, which are the primary feed for ruminants, are a poor source of P. A P deficiency can lead to many problems including reduced growth and feed efficiency, decreased appetite, reduced reproduction efficiency, decreased milk production, and weak or fragile bones (rickets).

When balancing rations, it is often stated that the Ca:P ratio needs to be 2:1, but this is overstated and anything from a 1.1:1 to a 7:1 ratio is acceptable, with optimal being 1.75:1. Due to the abundance of these minerals in the body, it is important to understand their function and know what the implications are for not meeting an animal’s nutrient requirements. Requirements vary based on animal class, size, and stage of production. Below is a snapshot of Ca and P requirements of cows, replacement heifers and calves taken from the Nutrient Requirements of Beef Cattle.

Source: Adele Harty



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