Dairy Channel: Reduce manure phosphorus to improve dairy profits, protect water resources


According to researchers at Cornell University, reducing excess feeding of phosphorus and nitrogen in the forms of protein and non-protein nitrogen should be a goal of well-managed dairy farms.

Applying manure nutrients in excess of crop requirements increases risk of nutrients ending up in surface or ground water. Feeding phosphorus and protein in excess of animal requirements contributes to this risk and is a costly waste of these expensive feed nutrients.

Safety in rations. Nutritionists typically include safety factors in rations for many nutrients. This is done to maximize production and to minimize the chance of nutrient deficiencies when feeds are not analyzed or are inconsistent in quality.

Safety factors also help to offset variations in feed intakes and production levels within a given group of animals. Research shows that the use of large safety factors, such as feeding a ration containing .45 percent P instead of the required .41 percent, can release large amounts of nutrients into the environment – more than 800 pounds annually from 100 cows

Improved methods of managing critical control points in the production, storage, analysis and feeding of homegrown feeds are available. Better understanding of the analysis of feedstuffs and the nutrient requirements of cows can allow managers to reduce ration safety factors while maintaining or continuing to improve production.

Major limitation. According to T. P. Tylutki and D. G. Fox of Cornell’s animal science department, a major factor limiting the adoption of reduced ration safety factors is the level of management required on dairy farms to achieve this goal. High levels of management are required to improve silo management, feed analysis, feeding accuracy, feed bunk management, and monitoring dry matter intake.

One of the most critical areas of management affecting profitability and nutrient accumulation on the farm is the quality and quantity of homegrown feeds. The quality of homegrown feeds is affected by stage of maturity and moisture content at harvest, minimizing variability of crops grown, and storage management.

A 1999 study at Cornell showed that variations in corn silage dry matter and fiber at harvest could result in variations of $40,000 or more in income over feed costs in a 100 cow herd.

Feeding accurately. The first step in accurately feeding phosphorus to any animal group is using accurate feed composition values.

Standard feeds like 48 percent soybean oil meal may vary from .57 percent to .76 percent phosphorus. Alfalfa haylage typically varies from .27 percent to .38 percent. These differences can result in dramatic variations in the amounts of supplements required in a ration. You can’t afford to use book values for purchased or homegrown feeds.

The next step is to accurately determine the phosphorus required in the ration. Dry matter intake monitoring is absolutely critical in getting the correct amount of any nutrient into the cow. A requirement of 100 grams for a cow consuming 55 pounds of dry matter requires a ration concentration of .40 percent phosphorus. If the cow is only consuming 40 pounds of dry matter, the concentration must be .55 percent.

Dietary needs. The form of phosphorus you feed is another critical factor in meeting the dietary needs of the cow as well as how much is excreted into the manure.

Phosphorus is absorbed in the small intestine. It is essential for energy metabolism and proper blood buffering. Absorption is dependent on the source, level of intake, intestinal pH, animal age, and the amounts of other minerals in the diet.

Inorganic sources of phosphorus can be ranked from highest to lowest availability as follows: sodium phosphate, phosphoric acid, monocalcium phosphate, dicalcium phosphate, defluorinated phosphate, bone meal, and soft phosphates.

Much of the reason nutritionists have given for overfeeding phosphorus is to make sure cows have adequate amounts for good reproductive performance.

No differences found. A 1999 Cornell study summarized 13 nutrition trials where nutrient levels varied from .32 percent to .61 percent of the ration. No differences were found in any of the trials in days to first heat, days open, services per conception, days to first breeding, or pregnancy rate.

The same researchers also summarized data from a number of other trials that varied the phosphorus level to determine differences in milk production. As above, as long as the grams of the nutrient required daily were provided, no differences were seen in milk production.

Ration balancing programs such as the Cornell Net Carbohydrate and Protein System can be used to evaluate mineral balances, calculate macro-mineral excretion, and optimize mineral utilization within groups. At the herd level, the software predicts herd phosphate and potassium excretion, efficiency of mineral use, and nutrient balance for the ration.

As you can see in Figure 1, the .45 percent phosphorus level results in excesses over most of the range of production levels.

Minimizing excretion. The ideas below are designed to reduce nutrient excretion while ensuring that milk production, growth, reproduction and animal health are provided for.

The goal can be met by two kinds of measures: decreasing phosphorus inputs by more accurately formulating rations, and improving the efficiency of nutrient utilization by improving feed and crop management.

Short term methods include use of more accurate ration formulation to decrease phosphorus fed to National Research Council requirements. This will decrease ration cost and excretion. There will still be nutrient overfeeding to some groups due to levels in the forages and concentrates in the ration.

Another method is to modify grouping strategies to improve accuracy of matching rations to animal needs. Analyze all feeds. Develop a feed analysis and feed database protocol for your farm. These records should include all forages and concentrates. Reduce ration safety factors where possible.

Monitor dry matter levels of stored forages frequently. The impact of improper forage analysis and lack of control over dry matter content when mixing and feeding can result in a large variation in nutrient excretion and income over feed costs ($21,792 per 100 cows).

You should determine dry matter content of all forages at least twice weekly, and more often if wide fluctuations in intake are observed, then adjust as fed formulas as needed.

Up the accuracy. Improve feeding accuracy. Do not assume that you or your employees are feeding correctly. Track feeding accuracy to identify sources of variation and improve inventory management. Commercial software and hardware is available that can be linked to mixer scales to help you keep track.

Monitor dry matter intake to improve accuracy of ration formulation and animal performance. Track intakes. Watch body condition scores, feed inventories, and actual dry matter intakes. Improve feed bunk management to increase intake and consistency of animal performance. This includes daily cleaning and pushing up feed several times daily. More consistent dry matter intake allows more precise ration formulation.

Control the level of feed refusal. Make sure there is feed in front of cows at all times. But, the more precisely intakes are controlled the more precisely rations can be formulated, and the more homegrown forages and grains can be fed.

The right tools. Use the proper tools to track the impact of ration changes and feeding management: milk production, milk components, milk urea nitrogen content, and manure analysis.

Look at what is not being digested by the cow. If large particle fiber or corn grain is not digested, rations and feeding management need to be corrected. Secondly, look at manure nutrient analysis and monitor as ration phosphorus levels are reduced.

Improve silo management. Have adequate capacity to store different crop types and quality separately to increase accuracy in ration formulation. Minimize storage losses with good management.

Match cows to crops to soils. Alfalfa and corn are not always the best choices for dairy farms. Your nutritionist and crop consultant should work together with you to determine the best combination of crops to be grown, given the soils and topography of your fields.

Increase the amount of homegrown feeds in the rations. Improve forage quality by better crop and harvest management, and carefully choose grains and concentrates that compliment your forages to reduce costs and improve production.

Nutrient application. Manage nutrient application on crop fields. After all the above areas are addressed, nutrient excretions will probably exceed crop needs on most dairy farms. Apply manure nutrients according to crop needs based on manure analyses and soil tests. Consider expanding the land base serving the farm and exporting nutrients to non-livestock farms.

Accomplishing a reduction in nutrient excretion requires a team effort including the farm’s nutritionist, crop consultant, management team, and employees. Share your farm’s financial and environmental goals with all those involved so that all share your vision for the farm.

(Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)


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