title: Effects of nitrogen fertilization and maturity of bromegrass on nitrogen and amino acid utilization by cows.
abstract: Four nonlactating Holstein cows (593 kg) with ruminal cannulas were fed bromegrass hay that was fertilized with 0 or 89 kg of N/ha and harvested in the late-boot or full-head stage of maturity. Total tract apparent digestibility of N was less for full-head than for late-boot bromegrass (48 vs 64%; P less than .01) and was greater for N-fertilized than for unfertilized bromegrass (60 vs 52%, P less than .01). True N digestibility was greater (P less than .01) by cows fed late-boot hay than by those fed full-head bromegrass (85 vs 81%). Maturity did not affect N retention. Nitrogen fertilization increased N retained, both grams per day (70 vs 20; P less than .01) and as a percentage of N intake (P less than .01). Nitrogen and amino acid disappearance kinetics were determined in situ. Rate constants for N disappearance within rapidly and slowly degraded pools were not different among treatments, but because late-boot had a larger proportion of N in the rapidly degraded pool, overall disappearance rate for N was faster (P less than .05) for late-boot than for full-head bromegrass (12.0 vs 7.1 %/h). Treatment effects observed for individual amino acids were similar to those found for N. Both composition and kinetic data were needed to explain differences in N digestion and balance. Distribution of N within the forage had profound effects on the N economy of the cows.
authors.affiliation: Department of Animal and Range Science, North Dakota State University, Fargo 58105.
authors.forename: M A
authors.initials: MA
authors.lastname: Messman
authors.forename: W P
authors.initials: WP
authors.lastname: Weiss
authors.forename: D O
authors.initials: DO
authors.lastname: Erickson
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D004063:Digestion; D004435:Eating; D005260:Female; D005308:Fertilizers; D009584:Nitrogen / Q000378:metabolism* / Q000652:urine; D006109:Poaceae; D012417:Rumen / Q000502:physiology
chemical_list: D000596:Amino Acids; D005308:Fertilizers; D009584:Nitrogen