title: Influence of nitrogen fertilization and defoliation frequency on nitrogen constituents and feeding value of annual ryegrass.
abstract: Two experiments were conducted to determine the seasonal effects of N fertilizer (NF) and defoliation interval (DI) on specific N fractions within annual ryegrass (AR) and overall usage of AR N by growing lambs. In Exp. 1, NF (0, 112, 224, and 336 kg of N/ha) and DI of 2, 4, or 6 wk were factorially applied to AR plots. Both decreasing DI and increasing NF increased N levels in AR in a manner that depended on harvest date (NF or DI x harvest date interaction, P < .05). The proportions of .2% NaOH soluble N or soluble protein N were not affected (P > .05) by NF or DI. Although NF had no effect (P > .05) on in situ disappearance of DM, decreasing the DI seemed to reduce the severity of the season-induced reduction in DM disappearance (DI x harvest date interaction, P = .04). In Exp. 2, NF (0 or 224 kg of N/ha) and a DI of 2 or 6 wk were factorially applied to AR plots. Fresh, frozen AR was fed in semipurified diets (48% of DM as AR) to four wether lambs (23 +/- 1.3 kg) using a 4 x 4 Latin square. Diets including AR had greater ruminal DM and plant N digestibilities when AR had a 2-wk vs a 6-wk DI with NF but had reduced digestibilities when AR had a 2-wk vs a 6-wk DI without NF.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Dairy Science, Louisiana State University Agricultural Center, Baton Rouge 70803, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: L D
authors.initials: LD
authors.lastname: Bunting
authors.forename: L C
authors.initials: LC
authors.lastname: Kappel
authors.forename: J L
authors.initials: JL
authors.lastname: Hafley
mesh_terms: D000821:Animal Feed / Q000032:analysis / Q000592:standards; D000818:Animals; D003678:Defoliants, Chemical / Q000737:chemistry / Q000494:pharmacology*; D005308:Fertilizers / Q000032:analysis / Q000592:standards*; D008129:Lolium / Q000737:chemistry*; D008297:Male; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D009753:Nutritive Value; D012756:Sheep / Q000254:growth & development / Q000378:metabolism*
chemical_list: D003678:Defoliants, Chemical; D005308:Fertilizers; D009584:Nitrogen