Nitrogen Metabolism of Beef Steers Fed Either Gamagrass or Orchardgrass Hay With or Without A Supplement

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Title: Nitrogen Metabolism of Beef Steers Fed Either Gamagrass or Orchardgrass Hay With or Without A Supplement
Author: Magee, Kelly Jean
Advisors: Gerald B. Huntington, Committee Chair
Abstract: This experiment evaluated rumen protein:energy synchronization in steers fed either gamagrass (Tripsacum dactyloides) or orchardgrass (Dactylis glomerata) hays with or without a soybean hull/corn supplement. A N balance trial was conducted to compare the effects of the supplement and hay on N intake, N digestion, and N metabolism. The supplement consisted of 50:50 corn: soybean hulls mix with 50 g molasses per kg of corn: soybean hulls mixture. The supplement contained 11.3% CP, 34.2% NDF, 22.9% ADF, and 0.87 kg was fed at 0830 and 1600 followed by hay offered in two equal portions. Steers had ad libitum access to water and a trace mineralized salt block throughout the study. Hay compositions were 8.3% CP, 71.8% NDF, and 37.8% ADF for gamagrass and were 11.9% CP, 70.5% NDF, and 36.6% ADF for orchardgrass. Steers were individually fed, blocked into two weight groups, and randomly assigned to either gamagrass or orchardgrass hay (4 steers per hay). Within hays, steers were assigned to receive supplement or no supplement in a crossover design. Ad libitum DM intake for each steer was equal to their intake during the last 8d of the 21-d ad libitum period. Steers were then placed in metabolism crates for an 8-d adjustment followed by a 5-d balance trial. During the balance trial, steers were fed 90% of ad libitum intake. Compared with gamagrass, orchardgrass had similar true IVDMD (64.2 vs 62.2%), similar leaf true IVDMD (58.2 vs 63.2%), and similar stem true IVDMD (46.7 vs 51.7%). Effects were significant at P < 0.10. Compared with gamagrass, orchardgrass had a lower ad libitum DM intake (4.62 vs 5.37 kg/d), higher N intake (96.6 vs 81.1 g/d), similar fecal N (36.1 vs 34.5 g/d), higher N digestibility (62.4 vs 57.4 %), similar N retained (27.2 vs 27.7 g/d), and lower digestible DMI (3.20 vs 3.53 kg/d). Compared with no supplement, supplement increased digestible DM intake (3.70 vs 3.03 kg/d), total DM intake (5.87 vs 5.07 kg/d), N intake (96.9 vs 80.8 g/d), fecal N (39.4 vs 31.1 g/d) and N retained (31.7 vs 23.2 g/d). Supplement (1.74 kg/d) decreased hay ad libitum intake by 0.73 kg/d. Supplement decreased, blood urea N, urine urea N and urine urea N as a percentage of urine N more for orchardgrass than for gamagrass. Supplement tended (P < 0.11) to improve N retained as a percentage of N intake or percentage of N digested more for orchardgrass than for gamagrass hay. Blood urea N was reduced (2.21 vs 0.14 mM)more for steers fed orchardgrass hay than for steers fed gamagrass. We believe that the increase in digestible OM intake is due in part to the presence of soybean hulls in the supplement.
Date: 2004-04-12
Degree: MS
Discipline: Animal Science

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