Abstract
The effect of various moisture contents of fresh forage on the change in nitrogen (N) fractions, in vitro ruminal N degradability, and the subsequent N utilization of silage in sheep were evaluated. Orchardgrass (Dactylis glomerata L.) with high (HM, 76%), medium (MM, 65%) and low (LM, 40%) moisture contents were ensiled into silos of 120 L capacity for 120 days. A nitrogen balance trial was conducted using a 4×4 Latin square design consisting of four dietary treatments (i.e. fresh forage, HM, MM and LM silages) and four wethers. With respect to N fractions, fraction 1 (buffer solution soluble N), fraction 2 (buffer solution insoluble N- neutral detergent insoluble N), fraction 3 (neutral detergent insoluble N-acid detergent insoluble N), and fraction 4 (acid detergent insoluble N) were determined. The proportion of fraction 1 in silages tended to decrease, while the in vitro ruminal degradability of insoluble N increased (p<0.05) with lower moisture contents at ensiling. Consequently, nitrogen utilization in sheep tended to improve as the moisture content of ensiled grass was decreased, with a negative correlation (p<0.01) between urinary N and the in vitro ruminal degradability of insoluble N. The averaged N retentions for HM, MM, and LM silage treatments were 59, 73 and 79% of that for fresh forage, respectively. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 9 : 1267-1272)
Highlights
It is well known that when fresh forage is ensiled, fermentation results in quality changes that alter the feed value of silage as compared to fresh forage
Very few data are available that show the effect of various moisture contents at ensiling on the change in N fractions of forage protein
The fractionation of forage nitrogen was as follows: Fraction 1, Fraction 2, and Fraction 3, calculated Chemical analyses by subtracting buffer solution insoluble nitrogen (BSIN) Fresh forage and silage were dried for 24 hours in a from total nitrogen (TN), neutral detergent insoluble freeze-drier (VD-40/TAITEC, Japan) to determine dry nitrogen (NDIN) from BSIN, and acid detergent insoluble matter (DM), being left in the experimental room for 7 days nitrogen (ADIN) from NDIN, respectively; and Fraction 4 to prepare air-dried samples
Summary
It is well known that when fresh forage is ensiled, fermentation results in quality changes that alter the feed value of silage as compared to fresh forage. The extent of true protein breakdown varies owing to several factors such as plant species, rate and extent of pH changes, moisture content and temperature, but it may reduce the protein content by 50 to 60% of original herbage, even in well-preserved silages (McDonald et al, 1991). Such changes in the nitrogenous components adversely affect the subsequent utilization of N in ruminants (McDonald et al, 1991; Nguyen et al, 2004a, b). Objectives of this study were to clarify the extent of change in N fractions and in vitro ruminal N degradability of orchardgrass silage as ensiled at high (76%), medium (65%), and low (40%) moisture contents respectively; and to evaluate the subsequent influence on N balance in sheep
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