*A. DiCostanzo is a professor of beef cattle nutrition at the University of Minnesota in St. Paul. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]
EARLY feedlots were designed based on considerations for cattle comfort, feed delivery, pen observation and cleaning but independent of the need to capture manure nutrients for recycling.
As fertilizer prices have increased, considerations by feedlot owners and operators for retaining the nutrient value of manure have responded accordingly. Thus, analyses of the net return to the entire farming/feeding operation from incorporating manure as fertilizer must be made to evaluate the effects of feedlot design on fertilizer and the ultimate value of manure to cattle feeders.
A single data set provided by Extended Ag Services Inc. contained nutrient analysis (as-is) results of 580 manure samples collected from 2010 to 2013 from open-design feedlots, manure bed packs from confinement feedlots — mostly monoslope structures — stockpiled manure (solid manure), manure samples from feedlot pits under slatted floors and lagoons (liquids).
A single data set containing data for either 86 liquid or 373 solid manure samples was analyzed for the effects of feedlot design on manure nutrient content. Manure nutrients were expressed as pounds of nitrogen, phosphate or potash per ton of as-is material (solid) or as pounds of these nutrients per 1,000 gal. (liquid).
In addition, a combined data set (n = 249) was analyzed with projected annual cattle manure production values of three and five tons per head or 2,500 gal. per head, respectively, for an outdoor or manure pack or slatted-floor feedlot over a pit to compare the effects of facility design on manure nutrient contributions per head space.
As expected, greater manure nutrient capture was observed from feedlots that rely on manure packs or have slatted floors over pits. Manure production estimated from pits yielded greater yearly amounts of nitrogen — at 121 lb. of nitrogen per head space — than that estimated from either manure bed pack at 89 lb. or outdoor feedlots at 48 lb.
Likewise, yearly yields of phosphate and potash were similar for confinement feedlots on pits and those with manure packs but were greater than for open-design feedlots — 58 lb. or 55 lb. versus 31 lb. of phosphate per head space and 95 lb. or 77 lb. versus 48 lb. of potash per head space, respectively.
This is a result of a greater potential to retain nutrients in a pit than from a bed pack or an exposed outdoor lot.
Comparing the estimated manure nitrogen yield from slatted-floor feedlots over pits using manure samples contained in this data set with the American Society of Agricultural Engineers standards "ASAE D384.2" — wherein values were derived from the simple production of urine and manure to represent the maximum manure nitrogen recovery values — demonstrated a recovery of 92% of the total nitrogen excreted by a single animal unit space yearly.
Applying the same logic, and ignoring the contributions of bedding material in manure bed pack barns, these barns recover 68% of the total nitrogen excreted by a single animal unit space yearly.
Zehnder et al. (2000) demonstrated that nitrogen recovery values approached 75% in manure bed pack buildings in the winter, while only 50% of nitrogen produced by the animal was recovered in the summer. The corresponding nitrogen recovery value for outdoor feedlots using this approximation is 37%.
These values agree well with those used by many agricultural engineering firms, consultants and feedlot owners.
Using the derived manure nutrient concentrations, fertilizer prices and hauling costs, a net value per head space can be calculated to determine differences in net nutrient value as influenced by feedlot design.
Fertilizer prices used (as of May 2014) were $740, $550 and $450 per ton for anhydrous ammonia, diammonium phosphate and potash, respectively. Costs were $3 or $4 per ton to haul manure from open or manure bed pack feedlots, respectively, and 1.5 cents/gal. to haul manure from feedlots with slatted floors over pits.
The resulting net yearly values for nutrient yield from open feedlots or manure bed pack feedlots were $19 and $30 per head, respectively. The net yearly value for nutrient yield derived from feedlots with slatted floors over pits was $51 per head.
An Excel-based decision support model was used to integrate the impact of corn grain yield (200 bu. per acre), feed efficiency (7 lb. of dry matter intake per pound of gain) and fertilizer price (as listed above) to determine the gross return creditable to corn acres. This model considered feeding a 750 lb. feeder that will sell at 1,400 lb. with a gain of 3.3 lb. per day.
Modeling these variables to determine the corn grain price when considering credit for grain use as feed, residue use as bedding or roughage, debit for residue removal and credit for value of manure derived from a manure pack feedlot (using data derived from the current analysis) resulted in a price of $4.96/bu. of corn — 20-50 cents/bu. greater than current elevator prices in northwest Iowa.
The Bottom Line
Incorporating the value of manure as fertilizer, given current feed, feeder cattle and corn grain prices, improves the return on corn acres planted to feed cattle relative to selling corn grain at the local elevator. This fact alone explains increased interest in feedlot expansion in the Upper Midwest.
Yet, feedlot design affects manure nutrient values; therefore, feedlot design must be considered when planning an expansion.
Although greater manure nutrient levels were found using this analysis for feedlots with slatted floors over pits, the reader must be reminded that this observation represents only a partial cost-to-benefit ratio. Location, capacity, siting, permitting, construction, management, bedding material choice and procurement, cattle type, days on feed, dietary ingredients and diets, feedlot life expectancy and many other factors influence the decision to choose one feedlot design over another.
Feedlot owners or operators who are considering building a new feedlot or expanding would be well advised to spend considerable time visiting existing feedlots and talking with other feedlot owners and operators to gather information on other advantages and disadvantages in each feedlot design available today before making the initial appointment with an agricultural engineer and the appropriate regulatory officer in their state and county.
ASAE. 2005. Manure production and characteristics. American Society of Agricultural Engineers Standards. D384.2 MAR2005. Accessed at: http://evo31.ae.iastate.edu/ifafs/doc/pdf/ASAE_D384.2.pdf.
Zehnder, C.M., A. DiCostanzo, K. Thate, R. Gilland, M.J. Murphy and T.R. Halbach. 2000. Health and environmental implications of using composted municipal solid waste as bedding in cattle feedlots. J. Anim Sci. 78:495-503.