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Utilization of Urea, Uric Acid and Caged Layer Waste by Ruminal Microorganisms Continuously Cultured in Vitro^1,2,

University of Maryland³, College Park 20742 and and US Department of Agriculture, Beltsville MD 20705

Abstract

Duplicate trials were conducted to determine utilization of urea (U), uric acid (UA) and poultry excreta from caged laying hens (CLW) by ruminal microorganisms continuously cultured in vitro. Each trial consisted of a 3 X 4 factorial arrangement of treatments with 12 fermentors. Every 66 min, a basal diet (20.3 ± .4 g dry matter) consisting mainly of corn meal (62.8%) and cornstalks (35%) was supplied to each fermentor. Amounts of the three N sources were varied to provide 10.7, 13.1, 14.2 and 16.0% crude protein (CP). Each trial lasted 11 days, and composite effluent samples collected on days 6 and 7, 8 and 9 and 10 and 11 were analyzed. Total VFA production (millimoles/gram dry matter fed) was lowest (P<.05) in cultures receiving CLW. More protozoa were maintained in cultures receiving CLW than in those receiving U or UA. Ammonia N (NH₃N) accumulation was 7.47, 3.68 and 4.61 mg/100 ml in cultures receiving U, UA and CLW, respectively. Protozoa and NH3N concentrations increased linearly (P<.01) with increasing N input. Methane and carbon dioxide production (millimoles/day) were not significantly affected by type or amount of N. Organic matter and fiber digested increased as N in the diets increased. Hemicellulose digested was increased by CLW. Bacterial N production, estimated by ¹⁵N or total precipitable N (TPN) analysis, was lowest in cultures receiving CLW; production did not differ between cultures receiving U and those receiving UA. Increases in N input had no significant effect on daily bacterial N production based on ¹⁵N or TPN analysis. There was a trend toward maximum bacterial N synthesis at 13.1% CP, or less than 5 mg NH₃N/100 ml, regardless of N source. Ruminal microorganisms continuously cultured in vitro are efficient scavengers of N, regardless of dietary N source.

¹ Conducted under cooperative agreement between the Maryland Agr. Exp. Sta., College Park, and USDA, Beltsville Agr. Res. Center, Beltsville, MD.

² Scientific Article No. A2673, Contribution No. 5718 of the Maryland Agr. Exp. Sta., Dept. of Anim. Sci.

³ Dept. of Anim. Sci.

⁴ Present Address: Dept. of Anim. and Vet. Sci., West Virginia Univ., Morgan town 26506.

⁵ Ruminant Nutr. Lab., Animal Science Institute.