Nutritional and management methods to decrease nitrogen losses from beef feedlots.
Nitrogen losses from open beef feedlots are a concern. Methods that decrease volatilization losses will lead to greater manure N, which is likely to be beneficial in open lot beef operations. Twelve or more pens were dedicated to N research whereby N intake, retention, and excretion were quantified and a mass balance conducted using manure, runoff, soil balance, and loss quantities. The objective was to decrease N volatilization losses or increase manure N or both. Dietary CP affects N excretion and N volatilization losses. Four experiments across 2 yr compared industry average CP (13%) to diets that were phase-fed to not exceed protein requirements (12.1 to 10.9%). Phase-fed cattle excreted 12 to 21% less N (P < 0.01), and N volatilization losses were reduced 15 to 33% (P < 0.01). In 2 other experiments, phase-fed diets were formulated to recycle undegradable intake protein. Steer G:F was similar (P = 0.18) or improved (P = 0.09), whereas N excretion and N volatilization losses tended to be reduced (P < 0.11) and N in manure was not affected (P > 0.35) compared with cattle fed 13% CP. Feeding less protein did not affect manure N, indicating manure N from open lots is related to other factors. A series of experiments evaluated increasing OM on the pen surface to increase N in manure. Feeding less digestible diets using fiber increased manure N (P < 0.01) and decreased (P < 0.10) N volatilization losses in 2 experiments conducted from November to May, but did not affect (P > 0.30) manure N or volatilization losses during 2 summer experiments. Adding bedding (i.e., OM) increased manure N in the winter as well. Another method evaluated was increasing pen cleaning frequency, which decreased N volatilization losses by 19 to 44% and increased manure N by 26 to 41% across 3 experiments. Other methods, such as acidifying manure by manipulating dietary cation anion difference, clinoptilite zeolite clay addition, and feeding different amounts of by-products had variable impacts on N volatilization losses. No treatments markedly affected runoff N, which is <5% of excreted N. Dietary protein affects N volatilization losses but not manure N. Other factors, such as OM on the pen surface, affect manure N. Cleaning manure frequently, which decreases exposure of manure N to air, decreases volatilization losses. Treatments should be evaluated across seasons due to seasonal effects.
Erickson
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G
Department of Animal Science, University of Nebraska, Lincoln, NE 68583-0908, USA. geericks@unlnotes.unl.edu
Klopfenstein
T
T
D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology*; D000818:Animals; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism / Q000502:physiology; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000378:metabolism; D004787:Environmental Pollution / Q000517:prevention & control; D006799:Housing, Animal; D008297:Male; D008372:Manure; D009584:Nitrogen / Q000378:metabolism*; D012621:Seasons; D018505:Waste Management / Q000379:methods
D004044:Dietary Proteins; D008372:Manure; D009584:Nitrogen