Arkansas - Agricultural Communication Services - University of ...

AAES Research Series 488
fitted with a 1-mm screen (Arthur H. Thomas, Philadelphia,
PA) and subsequently analyzed for N, neutral-detergent fiber
(NDF), acid-detergent fiber (ADF), lignin, neutral-detergent
insoluble N (NDIN), and acid-detergent insoluble N (ADIN).
The NDF, ADF, and lignin analyses were conducted using
batch procedures outlined by ANKOM Technology Corp.
(Fairport, NY). Nitrogen was quantified by a modified
Kjeldahl procedure (Kjeltech Auto 1030 Analyzer, Tecator,
Inc. Herndon, VA); the N concentration in NDF (NDIN) and
ADF (ADIN) residues was determined by identical procedures
as total N. All N components were reported on the basis
of dry matter and total N.
Changes in forage nutritive value over the six sampling
dates were tested for treatment effects using a split-plot
model using PROC GLM of SAS (SAS Inst., Inc., Cary, NC).
Concentrations of initial bale moisture served as the wholeplot
term and sampling dates were evaluated as the sub-plot
term. Whole-plot treatment effects were tested for significance
with the initial bale moisture x block interaction mean
square as the error term. The effects of sampling date and the
bale moisture x sampling date interactions were tested for
significance with the residual error mean square. Fisher’s
protected least significant difference test was used to separate
treatment means.
Results and Discussion
Measurable changes in concentrations of fibrous components
were expected in hays baled at all three concentrations
of moisture because the driest hay in this study exceeded
the 20% threshold for acceptable storage suggested by
Collins et al. (1987). Typically, fibrous components are not
lost during hay storage; concentrations are thought to
increase via indirect mechanisms due to preferential oxidation
of non-fiber components, particularly nonstructural carbohydrates
(Rotz and Muck, 1994). Sampling date x bale
moisture interactions were found (P < 0.05) for concentrations
of most fibrous components; therefore, only interaction
means are presented and discussed (Table 1). Generally, concentrations
of all fibrous components (NDF, ADF, and lignin)
increased over time in storage for hays baled at all concentrations
of moisture. Overall, the total change in NDF for HM
bales across the 65-d storage period was 10.5 percentage
units. Increases in concentrations of NDF over the 65-d storage
period for MM and LM bales were 8.2 and 8.0 percentage
units, respectively. Lignin exhibited the largest increases
in concentration of all fibrous components on a percentage
basis. Relative to d 0, concentrations of lignin increased (P <
0.05) by 30.7, 30.7, and 25.5% by d 65 for HM, MM, and LM
bales, respectively.
In most cases, large increases (P < 0.05) in the concentrations
of fibrous components were observed during the first
12 d of storage, but these fractions typically stabilized thereafter.
This pattern was observed consistently for all fibrous
components across all concentrations of moisture at baling.
Increases in concentrations of NDF (8.8 percentage units) and
ADF (6.5 percentage units) for HM bermudagrass hays were
observed by d 12 of storage. Further increases (P < 0.05) in
the concentrations of fibrous components were sometimes
observed; however, changes in concentration observed after
the initial 12 d of storage tended to be relatively small compared
to the rapid changes that occurred initially.
Concentrations of total N increased slightly (P < 0.05)
in MM and HM bales. In the short term ( 0.05) between d 0 and 65; this result was not unexpected
based on the limited heating that occurred in
these bales.
Concentrations of ADIN increased (P < 0.05) over time
in storage for MM and HM bales, but did not (P > 0.05) in
LM bales. The maximum proportion of N bound in the ADF
matrix in HM bales accounted for nearly 18% of the total
plant N (at d 24), and more than 10% (at d 65) of total N in
MM bales. These findings are consistent with previous work
(Coblentz et al., 2000) for bales packaged at comparable concentrations
of moisture that accumulated similar increments
of heat. Previously, Van Soest (1982) has suggested that feedstuffs
can exhibit variable sensitivities to nonenzymatic
browning. Sensitivity to nonenzymatic browning is an important
consideration in the nutrition of ruminants; ADIN in forages
is generally considered to be ruminally undegradable
(Sniffen et al., 1993) and to have very low bioavailability
(Licitra et al., 1996). Concentrations of NDIN increased (P <
0.05) over the 65-d storage period for all hays, while concentrations
of cell-soluble N (NDSN) decreased (P < 0.05) over
this period. The total change in concentration of NDIN in the
HM bales was 0.57 percentage units DM, which was greater
than that observed previously in bermudagrass hay packaged
at 32.5% of moisture (Coblentz et al., 2000). Overall, the proportion
of N associated with the residual NDF matrix
accounted for approximately half the total plant N on d 0
(mean = 50.7% of N), but this proportion increased (P < 0.05)
to 59.8, 65.4, and 69.0% of N in LM, MM, and HM bales,
respectively, after 65 d in storage. The magnitude of these
increases clearly reflects the differences in the heat increments
accumulated by each treatment.
Implications
Spontaneous heating resulted in elevated concentrations
of fibrous and fiber-bound N components. Changes in
the nutritive value of the hays were greatest during the first
12 d of storage; this period corresponded with the most active
period of spontaneous heating in our experimental hay bales.
A reduction in the bioavailability of N is likely to occur due
to the increase in fiber-associated N observed in these bales.
115