Differences in Drying Method of King Grass (
Pennisetum hybrid
)
Silage Samples Prepared for
in Vitro
Digestibility Analysis
A. Sofyan* & H. Herdian
Division of Animal Feed and Nutrition,
Research Unit for Processes Development and Chemical Engineering (BPPTK), Indonesian Institute of Sciences (LIPI),
Jl. Jogja-Wonosari Km. 31, Gading, Playen, Gunungkidul, DIY 55861 Indonesia Telp/Facs: 0274-392570/391168, *email: sofyan_lipi@yahoo.co.id
Abstract
In vitro digestibility of silage was influenced sample preparation methods because silage contained volatile compounds had potentially losses during preparation. An experiment had been conducted to evaluate different methods for preparing of a silage sample which was used in vitro digestibility studies. King grass (Pennisetum hybrid) silage were sampled at 21 d incubation for in vitro gas production analysis. Sample preparation was conducted by oven drying at 60°C while freeze drying method at -20°C and both of them conducted during 20 hours. The variables measured were in vitro dry matter and organic matter digestibility (IVDMD and IVOMD), gas production, volatile fatty acids (VFA) production. The experiment was arranged on completely randomized design with t-test analysis. Results showed that either IVDMD or IVOMD from silage dried by oven and freeze drying methods were similar. Production of volatile fatty acid (VFA) and acetate: propionate ratio (C2:C3) had also no differences between silage prepared by oven and freeze drying methods. However, total gas production from silage during 48 hours incubation affected by drying methods significantly (P<0.05). Gas production of freeze dried silage (Y) could be predicted by gas production from oven dried silage (X) as followed the equation was Y=1.0846X+0.7947 (R2=0.997). It was concluded that oven drying method could be used for the sample preparing method of silage at the in vitro digestibility analysis.
Key words: freeze drying, gas production, in vitro digestibility, oven drying, silage
Introducton
mcrobal fermentaton actvty whch produce volatle and unstable chemcal com-pound such as ammona, volatle fatty acds, and lactc acd (Rêgo et al., 2010). To overcome the problems, many researchers often use a freeze dryng technque for a better sample preparaton n future analyss (Grabber, 2009). However, there are lmtatons applyng ths method ncludng relatvely expensve equpment, more complex sample preparaton, etc. On the other hand, there are some relatvely sm-ple preparaton methods to proceed, such as oven dryng (Kamarloy and Yansar, 2008) or freeze dryng (Calabrò et al., 2005, Grabber, 2009).
It s necessary to nvestgate effects of substrate preparaton (.e. freeze versus oven dred) on in vitro dgestblty of kng grass (Pennisetum hybrid) on the bass of
in vitro gas producton technque. Ths s because sample preparaton method pro-duced hghly sgnfcant nfluence on in vitro degradaton test. Calabrò et al. (2005) ndcated that there was sgnfcant nteracton between sample method preparaton and fermentablty parameters. Total gas producton s known to gve a good estma-ton of dgestblty (Beuvnk and Kogut, 1993). Ths method s also able to predct fractons of rumen fermentable organc matter, crude proten and starch escapng rumen degradaton as well as in vitro organc matter dgestblty (DeBoever et al., 2005).
Therefore, the objectve of ths study was to nvestgate the effect of sample preparaton method on kng grass slage dgestblty based on determnaton of in vitro dry matter and organc matter dgestblty, total gas and volatle fatty acds producton usng gas producton technque.
Materals and methods
Slage was made from kng grass (Pennisetum hybrid). Grass was wlted for 24 hours to ncrease dry matter (DM) content. Feed materals were chopped wth shredded sze 1-3 cm. Inoculants 1% (v/w) was added nto grasses and water was also added to adjust mosture content up to 75%. After mxng homogenously, all ngredents were packed n plastc bag (5 kg/pack) and ncubated for 21 days. Samples were prepared by two methods of dryng. The frst group was dred by oven-dryng (60 °C) for 20 h, and the other one was dred by freeze-dryng method usng a freeze dryer Leybold-Heraeus GT Lyovac type-2 (Peterswan Ltd., Ednburgh) at -20 °C for 20 h. Samples were then ground wth a mortar and seved by a flter (1.0 mm screenng).
Ground slage samples (380 mg, DM 86.4%) were placed nto the syrnge to the pre-ncubaton for 24 h at 39 °C. Rumen flud (10 ml) and buffer soluton (20 ml) were nserted nto syrnge wth saturated CO2. Composton of buffer soluton per 100 ml rumen flud (Menke et al., 1979) conssted of macromnerals (23.7 ml), mcro-mnerals (0.012 ml), bcarbonate buffer soluton (23.7 ml), resazurn 4% (0.122 ml), reducng soluton (4.96 ml) and dstlled water (47.5 ml). Rumen flud was taken from fstulated beef cattle (Ongole crossbred) whch had been condtoned to feedng standard (feed composton conssted of 60% forage and 40% concentrate). Gas producton knetcs was calculated based on exponental equaton (Ørskov & McDonald,1979). The estmated value of a, b, c were calculated by fttng curve method usng Neway Software (Rowett Research Insttute, Aberdeen, UK) nstalled at Mcrosoft Offce Excel 2007® that was developed by Chen (1997). VFA was analysed usng gas chromatography method (Frggens et al., 1998) and NH3 analyss usng spectrophotometrc method (Broderck & Kang, 1980).
Evaluaton of in vitro dgestblty and fermentablty were arranged on completely randomzed desgn wth 2 treatments. Each treatment conssted of 3 replcatons wth 2 sub samples. Pangola grass (Digitaria decumbens) was used as standard sample and each syrnges contanng slage, standard samples and blank were randomly allocated n the ncubator. Incubaton was carred out for 48 h and gas producton was observed at 0, 1, 2, 4, 6, 8, 12, 18, 24, 36, and 48 h after ncubaton. Data of IVDMD and IVOMD, gas producton, VFA total, acetate (C2), proponate (C3), butyrate (C4), and NH
3 were analyzed wth analyss of varance (ANOVA)
and f among the treatments showed sgnfcant dfferences (P<0.05) followed by t-test (Gomez & Gomez, 2007).
Results and dscussons
Effect of dryng methods on in vitro IVDMD and IVOMD were shown at Table 1. IVOMD and IVDMD of slages prepared by freeze dryng method were 5%-6% hgher than those of slages prepared by oven dryng method. However, dryng methods had no sgnfcant nfluences on those varables. In vitro dgestblty of slage could be nfluenced by many factors whch were sample preparaton methods and chemcal component of feedstuff.
Calabrò et al. (2005) reported that there were no dfferences n OM degradablty (707 vs 708 g/kg) from slage dred by freeze- and oven- dryng (65 °C). VFA and ammona were readly vapor by ncreasng temperature n dryng chamber. Unstable chemcal compound (VFA and NH3) could be exhausted after slo was opened and slage was dred (Rêgo et al., 2010). To mantan volatle or unstable compounds, n slage could be conserved by freeze dryng (Grabber, 2009). Dfferences of dryng methods were sgnfcantly nfluence knetcs of gas producton durng 48 h ncubaton. Gas producton was hgher for freeze-dred sample than that of oven-dred sample (Fgure 1A). Ths result ndcated that gas producton from slage was hgher when t was prepared by freeze-dryng than by oven-dryng.
Gas producton obtaned from freeze-dred slage (Y) could be estmated by that from oven-dred slage (X) followng the equaton: Y= 1.085X+0.795 (R2= 0.998) (Fgure 1B). Ths equaton showed a sgnfcant analyss based on consstent ncreases n gas producton from both slages prepared by dfferent methods. Oven-dred slages could be used as estmaton of gas producton produced by freeze-Oven-dred slages. Denum and Maassen (1994) stated that forage dred at at 70 oC produced 1IVDMD: in vitro Dry Matter Dgestblty, 2IVOMD: in vitro Organc Matter Dgestblty, 3Gas
Producton from Soluble Fracton (a) and Potental Soluble Fracton (b), and Rate of Gas Producton (c), * Mean wth dfferent superscrpt at same row showed sgnfcant dfference (P<0.05).
Table 1. In vitro dgestbltes, gas producton parameters, producton of volatle fatty acd (VFA) and amona (NH3) from slage prepared by oven and freeze dryng
Varable Dryng Methods
Oven (60 °C) Freeze Dry (-20 °C)
In vitro dgestblty
IVDMD1 (%) 43.74±3.18 46.29±8.62
IVOMD2 (%) 50.61±3.01 53.83±10.55
Gas producton3
a (ml/h) -0.450±0.401 -0.518±0.479
b (ml/h) 48.32±2.623 50.746±4.675
a+b (ml/h) 47.87±2.517 50.227±4.580
c (ml/h)* 0.032±0.006b 0.025±0.003a
Total VFA (mM) 161.11±63.74 162.99 ± 79.10
Acetate (C2) (mM) 114.11±47.86 109.79 ± 54.89 Proponate (C3) (mM) 34.89±11.93 39.25±17.61
Butyrate (C4) (mM) 12.11±5.31 13.96 ±7.94
Rato C2:C3 3.20±0.63 2.75±0.39
less nutrent destructon, but dryng up to 105 oC caused more proten bound to NDF
fracton and ncreased other compound losses. Ths was due to Mallard reacton to occur between amno acd (proten) and glucose that strengthened chemcal lnkage n those fractons and less fermentable ndcated by lowerng gas producton.
Varables of soluble (a) and nsoluble fracton (b) showed non-sgnfcant df-ferences between sample prepared by both dryng methods. However, gas produc-ton rate (c) data was able to show nutrent loses produced by oven-dryng method. Fresh slage (200 mg) produced gas (45.6 ml) hgher than dred slage (32.4 ml) at 24 h ncubaton (Calabrò et al., 2005). Dryng at low temperature was able to keep volatle compound n slage, and ths type of slage could be smlar to that of fresh slage. Metaboltes n slage were domnated by organc acds such as lactc, acetc, proponc, and butyrc acds, N-ammona (McDonald et al., 1991).
There were no sgnfcant dfferences between oven- and freeze- dryng for slage preparng method on total VFA, acetate, proponate, butyrate and ammona. Average productons of acetate, proponate and butyrate were 112.0, 37.1, and 13.1 mM, respectvely, wth average rato of acetate (C2) and proponate (C3) was 2.98 and ammona producton was around 32.0 mg/100 ml. Calabrò et al. (2005) reported that freeze- and oven- dryng produced dfferent effects on corn slage, but were not statstcally sgnfcant. The results showed that total VFA (90.90 vs 82.94 mmol/g OM), acetate (65,60 vs 54.56 mmol/g OM), proponate (23.4 vs 22.26 mmol/g OM), butyrate (1.99 vs 3.03 mmol/g OM). Moreover, those dfferences value showed that not sgnfcant dfferences. Based on fermentablty varables, there were smlarty n responses between the two methods. Volatle compound produced by mcrobes durng enslage was not sgnfcantly lost when slage sample was prepared by oven dryng (60 °C, 20 h). A hgher dryng temperature caused many losses of compound n fresh forage decrease n dgeston rate, conversely a lower dryng temperature (50-70 °C) caused less several loses (Denum & Maasen, 1994).
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Concluson
There were no dfferences between oven-dred (60 °C, 20 h) and freeze-dred (-20 °C, 20 h) samples on n vtro dgestblty and fermentablty. Gas producton of freeze-dred slage (Y) could be predcted by that from oven-dred slage (X) usng the followng equaton: Y= 1.085X+0.795 (R2= 0.998). It was concluded that oven-dryng (60 °C, 20 h) method can be used for preparng slage samples n in vitro dgestblty analyss.
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