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Ration optimization models currently minimize the purchase price of feeds used to meet nutrient requirements. Not included in optimization models is the value of manure nutrients resulting from ration alternatives. This project extends the linear program that is used to minimize ration cost to include the value of manure excreted and stored. Microsoft EXCEL’s Solver GRG Nonlinear Add-in is used to optimize the integrated decision because of the non-linear aspects of manure excretion as a function of feed fed.
Several economic and production changes over the last 10 years warrant an investigation of the impact of optimizing both feed and manure decisions simultaneously. Distillers Dried Grains with Solubles (DDGS) have become a common feed high in phosphorus, lessening the need for inorganic phosphorus sources. Including DDGS in the diet also increases the manure concentration of phosphorus. If phosphorus is needed on nearby crop fields, there is potential to increase manure value while simultaneously reducing feed cost. In contrast, feeding phytase may reduce feed cost, while reducing manure value if phosphorus in manure is valued. Feeding synthetic amino acids can also reduce feed cost while reducing the amount of nitrogen excreted and available as a fertilizer in the manure. Adding to the importance of considering manure value is the increased costs of fertilizers. Manure is increasingly seen as a viable alternative to commercial fertilizers and might affect the whole farm profitability if included in the ration cost decision.
This project considers swine rations and examines how they might have changed during the past 10 years if manure value had been incorporated into the ration optimization decision. We will attempt to determine when manure fertilizer value relative to feed costs justifies integrating feed and manure optimization. Results indicate that incorporating manure value into the optimization routine would change some diet formulations.
Why Consider Manure Nutrients When Balancing Rations?
The value of manure supplied nutrients (N, P and K) has increased significantly over the past decade. Feedstuffs, such as DDGS, have been incorporated into the diets in ways that reduce the need for P supplementation. These developments have moved manure from a waste product to a co-product in livestock production. By integrating feed and manure management decisions it was hypothesized that profit could be improved.
What Did We Do?
The 2012 version of the National Swine Nutrition Guide (NSNG) ration software contains an optimization model for least cost ration formulation that calculates the potential manure value associated with different optimized diets. This recognition of the value of manure is an important contribution.
We incorporated the value of manure (as estimated by the NSNG) into the least cost ration optimization routine so that the objective function changed from minimizing the cost of feed to minimizing the net cost of feed. Net diet cost was defined as the cost of feed less the value of manure. Optimization of this equation required the use of the GRG non-linear optimization routine of Microsoft EXCEL.
This project evaluated least cost swine rations and how they might have changed during the past 10 years if manure value had been incorporated into the ration optimization decision. We specifically examined rations for 50-100 lb. and 200-250 lb. pigs. Rations were optimized with the following limitations: 1) manure was/was not included in the objective function; 2) DDGS were/were not allowed as a feedstuff in the rations.
What Have We Learned?
Assuming that the full value of the manure could be obtained, incorporating manure into the least cost ration optimization reduced net diet cost seven of the last 10 years for 50-100 lb. and 200-250 lb. pigs when DDGS were allowed in the diets. The ten-year mean improvement in net diet cost was $0.61/ton with a range from $0 to $8.41/ton of feed. More typically differences were small, exceeding $1.00/ton only in 2005 and 2006. Increasing manure value required increasing feed cost by an a 10-year average of $1.14/ton. The uncertainty in extracting manure value may make farmers hesitant to increase feed cost in hopes of capturing additional manure value. Two years may provide insight into the opportunity to incorporate manure value into the least cost feed decision. In 2006, a savings of $8.41/ton of feed fed was obtained by including 40% DDGS in the 50-100 lb. pig diet; this savings required increasing the feed cost by $1.76/ton resulting in a $10.18/ton increase in manure value in associated excreted nutrients. In 2009, a net ration savings of $.61/ton was obtained by eliminating phytase which was in the original least cost ration formulation. Phytase reduced the need for expensive phosphorus feedstuffs but not sufficiently when the value of manure was considered.
Non-linear optimization routines may find local optima rather than a global optimum. A procedure needs to be developed that insures that the global optimum is found before incorporating manure into the least cost ration decision will become widespread.
Dr. Ray Massey, Extension Professor, Agricultural and Applied Economics, University of Missouri, firstname.lastname@example.org
John Lory, Extension Associate Professor of Extension, Division of Plant Science, University of Missouri
Marcia Shannon, Associate Professor, Swine Nutrition, University of Missouri
The 2012 version of the National Swine Nutrition Guide can be found at the U.S. Pork Center of Excellence (https://www.usporkcenter.org/product/national-swine-nutrition-guide/)
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