Cattle receiving grain are less likely to be
phosphorus deficient due to the higher phosphorus levels in grain compared to
forage. Rapidly growing cattle and lactating cattle are more likely to be
phosphorus deficient due to greater requirements.Trace Minerals for California Beef Cattle
University of California, Cooperative Extension
Phosphorus
Phosphorus is a required mineral in the diets of cattle and is the most prevalent mineral deficiency in the world. Large amounts are found in bone and phosphorus has many important functions. Low amounts of phosphorus result in reduced growth rate, inefficient feed utilization, reduced conception rates and decreased milk production. Weak, fragile bones, stiffness in joints, and a depraved appetite (chewing of wood, soil or bones) may be seen in cattle with low dieteary phosphorus.
Deficiencies typically occur when forage levels are less than 0.2 percent or
soil levels are below 0.02 percent. Cattle receiving grain are less likely to be
phosphorus deficient due to the higher phosphorus levels in grain compared to
forage. Rapidly growing cattle and lactating cattle are more likely to be
phosphorus deficient due to greater requirements.
Phosphorus deficient soils are common, producing phosphorus deficient plants. Mature forage, crop residues and alfalfa hay are typically poor sources of phosphorus. Cereal grain and oilseeds (like cottonseed meal) are good sources of phosphorus. Unfortunately, phosphorus is one of the more expensive ingredients in supplements. In spite of it's higher cost, when deficiencies of phosphorus occur, supplementation is cost effective.
Requirements for phosphorus in the diet vary but generally range from 0.20 to 0.25 percent, cattle with faster rates of gain and lighter body weight have even higher needs.
Heavily milking beef cows need 28 or more grams of phosphorus while average milking cows require about 22 grams daily. As a guideline, one pound of alfalfa has about 1 gram of phosphorus. Therefore beef cows on full feed of alfalfa will have adequate phosphorus only if they are average or below in milking ability. Specific requirements can be found in the National Research Council, Nutrient Requirements of Beef Cattle. Analyzing feed for phosphorus content can be adequate for determining phosphorus status of feedlot cattle. However, it is not practical for non-confined cattle.
Normal blood serum (the liquid part, blood cells removed, from the blood sample) phosphorus levels are 56 to 65 ppm. When plasma or serum levels are below 35 ppm, phosphorus deficiency should be considered.