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Nutritional Value of Eastern Gamagrass Conserved as Hay or Silage J-S. Eun, J. C. Burns, M. L. Gumpertz and V. Fellner IntroductionA shift to grass-based
dairying is seen as a mechanism to increase the sustainability and
profitability of dairy farms. Eastern gamagrass [Tripsacum dactyloides (L.)
L.] is a warm-season perennial bunch grass and possesses the same C4
photosynthetic pathway as does corn. Eastern gamagrass has high yields and
rapid growth and has recently gained renewed interest because of its
nutritive value as a forage crop, its ability to penetrate acid, compacted,
and marginal soil and to survive both flooding and drought. In addition, it
has the potential to create more sustainable silage production and to help
reduce soil erosion. High yielding, high quality perennial grass silage crops
are needed as alternatives to corn on marginal and sloping cropland (Brejda
et al., 1994). The forage quality of
eastern gamagrass is excellent if harvested at the proper stage of maturity
(Horner et al., 1985). The unique characteristics of gamagrass can contribute
to reducing the cost of producing milk and to meet more sustainable resource
management. However, there are
limited data on the feeding value of gamagrass for dairy cattle.
Additionally, efficient use of the forage requires an understanding of
synchronizing the availability of nitrogen and supplemental source of energy
to optimize microbial protein synthesis in the rumen. The objectives of this
study were to assess the feeding value of gamagrass as hay or silage for
dairy cows and to determine the effect of supplemental corn in gamagrass
silage-based diets. Kinetics of microbial fermentation in continuous cultures
were determined to better understand factors underlying nutrient utilization
of gamagrass conserved as hay or silage. Materials and Methods Twenty lactating
Holstein cows were selected for the lactation trial from the dairy herd at
the NC State Dairy Education Unit. Prior to the start of the trial cows were
grouped by parity and d in milk into 1 of 5 groups. They were allowed at
least 2 weeks to adjust to CalanÒ feeding gate prior to being randomly assigned to one of five dietary
treatments that were gradually introduced over 10 d. The five dietary
treatments were: 1) GHNC = gamagrass hay (GH) + no corn, 2) GSNC = gamagrass
silage (GS) + no corn, 3) GSLC = GS + low level of corn, 4) GSMC = GS +
medium level of corn, and 5) GSHC = GS + high level of corn (Table
1). All diets contained a protein supplement composed of soybean meal
(48% CP) and a vitamin and mineral premix. Experimental diets were formulated
based on estimated dry matter intakes to maintain a ration CP for similar
nitrogen (N) intakes. The total experimental periods with dietary treatments
lasted for 31 d and 52 d for cows fed GHNC and GS with or without ground
corn, respectively; 10 d were for dietary adaptation followed by 21 d and 42
d of data collection. The quantity of gamagrass hay was limited but adequate
for 3 weeks of data collection. All cows were
individually fed either hay or the total mixed ration (TMR) once daily for ad
libitum intake with amounts fed and feed refusal recorded daily. Samples of
the TMR and feed refusal were obtained daily during the trial, frozen (-20°C) immediately, composited by cow weekly,
dried at 65°C for 48 h, ground through a Wiley mill
(1-mm screen), and stored for subsequent analyses. Protein supplement, ground
corn, GH, and GS were sampled weekly during the trial and processed as
described above. Samples were analyzed for DM, ash, Kjeldahl N, neutral
detergent fiber (NDF), and acid detergent fiber (ADF) concentrations using
AOAC (1999). Non-protein N (NPN) concentration of the feed samples was
determined using trichloroacetic acid
precipitation (Licitra et al., 1996). Cows were milked twice daily, and milk
weights were recorded at each milking. Milk samples from individual cows were
analyzed for fat, protein, lactose, SNF, and milk urea nitrogen (MUN) by
United DHIA Laboratory (Blacksburg, VA). Total lipids of the milk samples
taken during the last week of the trial were analyzed for the fatty acid
profile. Data were analyzed using the repeated measures of PROC GLM of SAS. A
completely randomized design was used with the following model: Yij = m + Ti + eij, where Yij = the dependent
variable, m = the overall mean, Ti = the treatment
effect, and eij = residual error. To determine the effects
of gamagrass diets that were similar to those fed in a lactation trial on
microbial metabolism, artificial fermentors were incubated with filtered
ruminal contents and allowed to adapt for 4 d to diets followed by 3 d of
sample collection. Five dietary treatments were compared in a randomized
complete block design with 3 blocks as repeated runs. Culture contents were
analyzed for volatile fatty acid (VFA), pH, ammonia-N (NH3-N), lipid profile,
and microbial protein synthesis. Headspace gas was analyzed for methane
(CH4). Data were analyzed as repeated measures using the mixed procedure of
SAS with the following model: Yij = m + Ti + eij, where Yij = the dependent variable, m = the overall mean, Ti = the treatment
effect, and eij = residual error. Independent run was considered random. Results and Discussion Since cows fed GHNC received
their experimental diet for 21 d, data corresponding to the same 21 d period
for cows fed GSNC was used for statistical comparison between the two
treatments. Comparison of GSNC with supplemental corn diets was based on the
6 week data. Dry matter intake for cows fed GHNC or GSNC
averaged 14.3 and 14.6 kg/d, respectively and was not different (P > 0.10;
Table 2). Corn supplementation linearly increased (P
< 0.05) DM intake of cows. Substituting corn for silage resulted in a
lower silage intake. Nitrogen intake by cows fed GSNC averaged 0.46 kg/d and
was significantly lower when compared with GS diets with supplemental corn
(0.51 kg/d). The ratio between DM intake and body weight increased linearly
with corn supplementation. Feeding gamagrass as hay
or silage did not affect (P > 0.10) milk yield which averaged 27.6 and
29.5 kg/d for the two diets, respectively (Table 3).
Compared to GSNC, feeding supplemental corn increased (P < 0.10) milk yield
but only at the medium and high levels of corn inclusion. Milk fat
concentrations were similar across all treatments. Milk protein percentage
was similar between GHNC and GSNC but tended to increase at all levels of
corn inclusion when compared with GSNC. Yields of milk fat were similar
between GSNC and GHNC; corn supplementation at the low and high levels
supported greater yields when compared with GSNC. Corn supplementation
increased the energy content of milk. Gamagrass fed as silage
resulted in higher feed conversion efficiency compared to gamagrass fed as
hay (Table 4). Including corn with the silage lowered
feed efficiency with GSHC being the lowest. Conversion of feed N to milk N
was greater with gamagrass fed as silage compared to hay and supplementation
of GS with corn failed to improve N efficiency in cows fed low or medium
level of ground corn. Milk urea nitrogen (MUN) was significantly higher when
cows were fed GHNC (30.2 mg/100 ml) compared with GSNC (18.4 mg/100 ml).
Concentration of MUN was similar (P > 0.10) between GSNC and GSLC but
significantly lower at the medium (14.7 mg/100 ml) and high (13.3 mg/100 ml)
levels of corn inclusion. Concentration of the
total VFA was similar across all diets averaging 48.5 mM (Table
5).The molar proportions of acetate were higher with GH compared to GS.
Corn supplementation at the medium and high level resulted in the lowest
proportion of ruminal acetate. The molar proportion of propionate was reduced
in the GSLC diet and remained similar across all other diets. Butyrate was
higher in GS compared with GH. Corn supplementation increased molar
proportion of butyrate which was highest in cultures receiving the high level
of corn. The molar ratio between acetate and propionate decreased with medium
or high level of corn supplementation. Feeding GS resulted in a higher
ruminal pH compared to GH. Increasing the level of corn supplementation in GS
linearly decreased culture pH. Concentration of NH3-N was similar across
treatments (27.9 mg/100 ml) and tended to decrease with increasing levels of
corn. All diets resulted in similar methane production with the exception of
GSMC which lowered methane output. Including corn at the high level with
gamagrass silage did not have a detrimental effect on ruminal fermentation. Partitioning of feed
among VFA, gas (CH4 + CO2), and microbial biomass was similar between
gamagrass hay and silage (Table 6). Gamagrass silage
supplemented with the high level of corn increased the amount of substrate
used for VFA, gas, and microbial biomass. Total fermentability was higher in
cultures receiving GH compared to GS, and it increased linearly with
increasing level of corn supplementation. Digestibility of NDF was maintained
at a similar level across all treatments. Efficiency of microbial synthesis
was similar between gamagrass hay and silage and increased only at the high
level of corn supplementation. Microbial N flow was increased only with GSHC. Conclusions Gamagrass silage
supported similar milk yield compared to gamagrass hay. Increased energy from
supplemental corn increased milk yield and tended to increase conversion of
feed N into milk protein. Because reduced concentrations of MUN are
indicative of improved N status of cows, gamagrass improved the N status of
the cows fed silage without or with corn supplementation. Difference in N
efficiencies for cows fed gamagrass as hay or silage may be related to
changes in the protein fraction during the conservation process. In addition,
the ensiling process may alter the rate of N release in the neutral detergent
fraction of gamagrass. Microbial efficiency and microbial N flow was not
affected when gamagrass was fed as hay or silage but corn supplementation, at
the high level, was effective in increasing both. Gamagrass silage maintained
lactation performance similar to gamagrass hay. Gamagrass silage with corn
supplementation supported milk yield comparable to conventional corn silage.
Corn supplementation with gamagrass silage is an effective strategy to
increase passage of microbial protein. References AOAC.
1999. International Official Methods of Analysis. 16th ed. Association of
Official Analytical Chemists, Arlington, VA. Brejda, J.
J., J. R. Brown, J. M. Asplund, T. E. Lorenz, J. L. Reid, and J. Henry. 1994.
Eastern gamagrass silage fermentation characteristics and quality under
different nitrogen rates. J. Prod. Agric. 7:477-482. Horner, J.
L., L. J. Bush, and G. D. Adams. 1985. Comparative nutritional value of
eastern gamagrass and alfalfa hay for dairy cows. J. Dairy Sci. 68:2615. Licitra,
G., T. M. Hernandez, and P. J. Van Soest. 1996. Standardization of procedures
for N fractionation of ruminant feeds. Anim. Feed Sci. Technol. 57:347-358. Table 1. Ingredient and chemical composition of the diets.
1GHNC = gamagrass hay + no corn; GSNC = gamagrass silage + no corn; GSLC = gamagrass silage + low level of corn; GSMC = gamagrass silage + medium level of corn; GSHC = gamagrass silage + high level of corn. 2Protein supplement included 78.6% soybean meal (48% CP), 8.5% deflourinated rock phosphate, 2.5% calcitic limestone, 2.7% salt, 1.6% magnesium oxide, 5.4% sodium bicarbonate, 0.6% McNess 1401Ò. 3NFC (Nonfibrous carbohydrate) = 100 – (CP + NDF + fat + ash). Table 2. Intake of cows fed gamagrass hay (GH) or silage (GS) without or with supplemental corn1.
1GHNC = GH + no corn; GSNC = GS + no corn; GSLC = GS + low level of corn; GSMC = GS + medium level of corn; GSHC = GS + high level of corn. a,b,cMeans within the same row without a common superscript differ (P < 0.01). e,f,g,hMeans within the same row without a common superscript differ (P < 0.05). i,j,kMeans within the same row without a common superscript differ (P < 0.10). Table 3. Milk yield and composition from cows fed gamagrass hay (GH) or silage (GS) without or with supplemental corn1.
1GHNC = GH + no corn; GSNC = GS + no corn; GSLC = GS + low level of corn; GSMC = GS + medium level of corn; GSHC = GS + high level of corn. 2NEL = net energy content of milk. a,b,cMeans within the same row without a common superscript differ (P < 0.01). e,f,gMeans within the same row without a common superscript differ (P < 0.05). i,j,kMeans within the same row without a common superscript differ (P < 0.10). Table 4. Efficiencies of feed and nitrogen (N) utilization for cows fed gamagrass hay (GH) or silage (GS) without or with supplemental corn1.
1GHNC = GH + no corn; GSNC = GS + no corn; GSLC = GS + low level of corn; GSMC = GS + medium level of corn; GSHC = GS + high level of corn. 2Dry matter intake 3Fat corrected milk 4Milk urea nitrogen. a,bMeans within the same row without a common superscript differ (P < 0.01). e,f,gMeans within the same row without a common superscript differ (P < 0.05). Table 5. Total and individual volatile fatty acid (VFA), ruminal pH, ammonia-N concentration, and methane production in continuous cultures receiving gamagrass hay (GH) or silage (GS) without or with supplemental corn.
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