Effects of dietary nitrogen source and concentration in high-grain diets on finishing steer performance and nutrient digestion.
Two experiments were designed to evaluate dietary N source and concentration on finishing steer performance and nutrient digestion. In Exp. 1, 100 steers were used in a randomized complete block design experiment with 2 x 2 + 1 factorially arranged treatments. Diets contained 1.93 or 2.24% N supplemented by urea or soybean meal (SBM), or 2.24% N supplemented by cottonseed meal (CSM). Steers fed SBM-supplemented diets gained 13% faster (P < .01) and were 9% (P < .01) more efficient converting feed to gain than steers receiving urea. Steers fed diets containing 2.24% N were 4% (P < .05) more efficient than those fed diets containing 1.93% N. Steers fed CSM-supplemented diets gained 6% (P < .10) less efficiently than steers receiving SBM. Increasing dietary N with urea from 1.93 to 2.24% decreased carcass weights 3%, whereas increasing dietary N with SBM increased carcass weights 3%. Carcass-adjusted gains were reduced 8% by increasing urea from .9 to 1.5% but increased 7% by increasing SBM from 6.1 to 10.5% of DM. In Exp. 2, four ruminally and duodenally cannulated steers (390 kg) were used in a 4 x 4 Latin square design experiment to evaluate urea and SBM supplementation on digestion. Diets contained no supplemental N, 1.84% N with urea or SBM as the supplement, or 2.16% N with SBM as the supplement. Total tract starch digestion, duodenal microbial N flow, and efficiency of microbial protein synthesis in the rumen were higher (P < .10) in steers fed SBM- than in those fed urea-supplemented diets. Supplementation with SBM increased metabolizable protein supply and dietary energy utilization.
Milton
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Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506, USA.
Brandt
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Titgemeyer
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D000818:Animals; D001823:Body Composition / Q000187:drug effects / Q000502:physiology; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism* / Q000502:physiology; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000502:physiology; D002523:Edible Grain; D008297:Male; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism / Q000502:physiology; D013025:Glycine max / Q000737:chemistry / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism
D009584:Nitrogen