Phosphorus is rapidly becoming a concern due to water pollution issues
Phosphorus excretion is highly dependent on phosphorus intake
Summarized from the Journal of Dairy Science (vol. 85, pg. 1227)
Nutrient management plans in the United States are currently heavily focused on nitrogen. However, phosphorus is rapidly becoming a concern due to water pollution issues. Erosion control can effectively reduce phosphorus runoff. Unfortunately, continued excessive application of phosphorus relative to crop requirements has led to phosphorus saturation of the soil. The result is phosphorus runoff independent of erosion.
Historically, US producers significantly overfed phosphorus to their dairy cows. Much of this overfeeding was due to concerns that published phosphorus requirements were not adequate to support reproduction in high producing cows. Practical experience in Europe, as well as research findings from the University of Wisconsin in the United States (Wu and Satter, 2000; Wu et al., 2000; Wu et al., 2001), has shown that herd fertility will not be adversely affected by feeding phosphorus at published requirements.
Another common reason for phosphorus overfeeding is over-fortification of “high” cow diets to meet the needs of fresh cows with low dry matter intakes.
Phosphorus excretion is highly dependent on phosphorus intake (Morse et al., 1992), so feeding more phosphorus than is required will lead to excessive phosphorus levels in manure. On the other hand, in times of low phosphorus intake, cows have the ability to easily recycle phosphorus through their saliva. Phosphorus absorption in the small intestine is also increased when phosphorus intake is low (Hibbs and Conrad, 1966; Hibbs and Conrad, 1983).
Feeding phosphorus below the cow’s requirement will lead to a negative phosphorus balance and mobilization of body phosphorus reserves. There is some evidence in sheep that body phosphorus reserves will be replenished without increasing phosphorus feeding as requirements decrease (Braithwaite, 1983b). Researchers at the Virginia Polytechnic Institute and State University (USA) investigated the response of lactating dairy cows to feeding phosphorus with particular attention to phosphorus excretion (Knowlton and Herbein, 2002). These workers found that feeding higher levels of phosphorus not only increased excretion, but also did not consistently improve phosphorus retention. These workers proposed that phosphorus excretion might be reduced by accounting for release of tissue phosphorus due to catabolic processes in early lactation. However, they did note that below a certain level, prolonged negative phosphorus balance and depressed blood phosphorus content could result.
Braithwaite, G. D. 1983b. Calcium and phosphorus requirements of the ewe during pregnancy and lactation. 1. Calcium. Br. J. Nutr. 50:711-722.
Hibbs, J.W., and H. R. Conrad. 1966. Re-evaluation of nutrient allowances for high-producing cows. 2. Calcium, phosphorus and Vitamin D. J. Dairy Sci. 49:243-246.
Hibbs, J.W., and H. R. Conrad. 1983. The relation of calcium and phosphorus intake and digestion of calcium and phosphorus by lactating dairy cows. Ohio Agric. Expt. Stn., Wooster, The Ohio State University.
Knowlton, K. F., and J. H. Herbein. 2002. Phosphorus partitioning during early lactation in dairy cows fed diets varying in phosphorus content. J. Dairy Sci. 85:1227-1236.
Morse, D. H., H. Head, C. J. Wilcox, H. H. VanHorn, C. D. Hissem, and B. Harris, Jr. 1992. Effects of concentration of dietary phosphorus on amount and route of excretion. J. Dairy Sci. 75:3039-3049.
Wu, Z., and L. D. Satter. 2000. Milk production and reproductive performance of dairy cows fed two concentration of phosphorus for two years. J. Dairy Sci. 83:1052-1063.
Wu, Z., L. D. Satter, A. J. Blohowiak, R. H. Stauffacher, and J. H. Wilson. 2001. Milk production, phosphorus excretion, and bone characteristics of dairy cows fed different amounts of phosphorus for two or three years. J. Dairy Sci. 84:1738-1748.
Wu, Z., L. D. Satter, and R. Sojo. 2000. Milk production, reproductive performance, and fecal excretion of phosphorus by dairy cows fed three amounts of phosphorus. J. Dairy Sci. 83:1038-1041.