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Utilization by Fattening Cattle of Unfermented Manure and Two Residues Produced by Anaerobic Generation of Methane from Feedlot Manure^1,2,

University of California, Davis 95616

Abstract

Two fermented manure residues (FM) from the pilot plant anaerobic digestion of commercial feedlot manure for methane generation were compared with unfermented manure (UFM) in beef steer metabolism and comparative slaughter feedlot trials utilizing diets formulated to replace 10, 20 and 30% of a control diet with each manure product on an as-fed basis (about 90% dry matter). A 10/21 FM was produced by 21-d digestion of a 10% organic matter manure slurry and a 5/7 FM was produced by a 7-d digestion of a 5% organic manure slurry. Metabolism-trial-determined dry and organic matter digestibilities, digestible energy, and total digestible nutrients (TDN) decreased (P<.05) as level of manure product increased except, inexplicably, for UFM diets above 10% in which only TDN decreased with increased manure level. Extrapolated TDN values were 15.6% for 10/21 FM, 18.8% for 5/7 FM, and 44.3% for UFM. Feedlot trial performance indicated an increase (P<.05) in daily dry matter intake but a decrease (P<.05) in average daily gain and energy gain as level of manure product increased. Utilizing fasting heat production and energy deposition data for maintenance- and ad libitum-fed steers, estimated net energy values for maintenance and gain (Mcal/kg) were .05 and –.84 for 10/21 FM, .10 and –.76 for 5/7 FM, and .90 and –.14 for UFM. Thus, UFM had very little energy value for fattening cattle, and fermenting the manure removed any energy value the manure originally possessed. Consequently, manure scraped from the dirt-floor pens of a commercial feedlot, especially after fermentation in an industrially constructed methane generating pilot plant, was not considered an optional energy source for cattle fattening diets.

¹ Unfermented and fermented manures were produced in cooperation with the Pacific Gas and Electric and Southern California Gas pilot methane generating plant and Kershaw and Sons Feedlot located in Imperial Valley, CA.

² This research was partially supported by grants from Pacific Gas and Electric and Southern California Gas, Mrs. Walter Rosenberg and the Univ. of California Appropriate Technology Program.

³ Present address: Western Illinois Univ., Dept. of Agr., Macomb, IL 61455.

⁴ Dept. of Anim. Sci.