Effect of wilting, chopping length and different levels of maize bran on grass silage quality

B J Lyimo, E J Mtengeti¹, N A Urio¹ and E N Demanisho¹

Mvomero District Council, POBox 663, Morogoro, Tanzania.
bmwaluka2003@yahoo.com
¹ Department of Animal, Aquaculture and Range Sciences, College of Agriculture, Sokoine University of Agriculture, P O Box 3004, Morogoro, Tanzania.

Abstract

Appropriate technologies for conserving excess fodder grasses as silage in the wet season so as to reduce scarcity of feed in the dry season are still lacking among the smallholder dairy farmers in Tanzania. Therefore, the study was conducted to determine the effectiveness of wilting, chopping length and different levels of maize bran inclusion on elephant grass ( Pennisetum purpureum) silage quality. Elephant grass was harvested when its re-growth reached a height of 1.5 m. The harvested grass was divided into two portions. One portion of grass was wilted for 24 hours prior to ensiling while the other portion was ensiled un-wilted. Before ensiling each portion was divided into two sub-portions and the sub-portions chopped into either 2 or 4 cm pieces, respectively using a machete. Within each chop size (2 or 4 cm) the material was subdivided into four portions each of which were treated with four levels (0, 5, 10 and 15%) of maize bran. The experimental schedule comprised of two pre-ensiling treatments (wilted or un-wilted), two chopping lengths and four maize bran levels which were arranged in a 2 x 2 x 4 factorial arrangement of treatments with two replicates. The silage was opened and sampled after 60 days, analyzed for sensoric qualities; chemical composition, in vitro DM digestibility (IVDMD), fermentation characteristics and stability.

Silages produced from wilted grass, 2 cm chopped grass, grasses treated with maize bran at 10% level had better sensory scores, dry matter (DM), crude protein (CP), water soluble carbohydrate (WSC), lactic acids, acetic acids and stability but lower NH₃N and butyric acid than those produced from un-wilted, 4 cm chopped grass or grasses treated with other maize bran levels (0, 5 and 15%). It can be concluded that wilted elephant grass, chopped to 2 cm and treated with 10% maize bran, seemed to be the appropriate combination of techniques to improve fermentation and thus produce good grass silage under smallholder farmers.

Key words: elephant grass, pre-ensiling treatments, smallholder dairy farmers

Introduction

In the tropics, livestock production is often restricted by inadequate feed supply during prolonged dry seasons. Forage conservation in form of silage is an option to increase dry season feed availability. However, adoption of silage making among smallholders farmers in general has been limited (’t Mannetje 2000). This is due to lack of better understanding of silage-making principles, not only by farmers but also by extensionists (Rangnekar 2000). The main fodder grass established in East African highland, which has been extensively adopted by dairy farmers due to its high productivity and persistence, is elephant grass (Kitalyi et al 2005). However, both the DM and WSC in elephant grass are considered to be too low for successful ensiling (Lyimo 2010). Use of silage conservation technologies like, wilting, chopping and mixing additives to the fodder grass can improve fermentation process and therefore increase nutritional value of the silage. Wilting increases DM, WSC and reduces losses from effluent and undesired fermentation (Nussio 2005). Forage chopping may minimize Clostridium fermentation by promoting greater packing density and thus exclusion of air. Moreover, closer substrate contact with the fermenting bacteria leads to higher lactate yield and faster pH reduction (Balsalobre et al 2001). Adding carbohydrate-rich by products like maize bran promote the activity of epiphytic lactic acid bacteria. Despite these useful technologies, lack of better understanding of silage-making principles becomes a barrier (Rangnekar 2000). Farmers ensile their grasses without wilting, chopping or use of any additives. Others chop and wilt grasses without using any additives, chop grasses mixing them with additives without wilting or wilt and mixing them with additives without chopping. Others may also use these techniques incorrectly like, chopping grasses without knowing exactly optimal chopping length or inclusive levels of additives. These unbalanced practices hinder production of high quality silages and demoralize farmers. Therefore, the current study aimed at assessing the effect of wilting, chopping lengths and different levels of maize bran on grass silage quality.

Materials and methods

Study area

The study was conducted in Magadu dairy farm at Sokoine University of Agriculture (SUA) in Morogoro municipal, Tanzania. The study site was located at about 526 masl (S 6° 50' 58.80" E 37°39' 12.22" GPS coordinates). It is characterized by ambient temperature between 20 and 27^oC in the coolest months of April to August and 30 to 35^oC during the hottest months of October to February. The annual rainfall ranges from 600 to 1000mm.

Experimental design and treatments

The study adopted a completely randomized design with a 2 x 2 x 4 factorial treatment combination arrangement with two replicates. The experiment comprised of two wilting methods (wilted, un-wilted), two chopping lengths (2, 4 cm) and four levels of maize bran (0, 5, 10 and 15%).

Source, harvesting, preparation of ensiling fodder grasses, ensiling procedure and storage

Elephant grass was harvested at a height of 1.5 m re-growth. The harvested grass was divided into two portions. One portion of grass was wilted for 24 h prior to ensiling while the other portion was ensiled un-wilted. Before ensiling each portion was divided into two sub-portions and one sub-portion chopped into 2 cm and the other into 4 cm pieces by using a machete. Each chopped portion was subdivided into four lots that were respectively treated with four levels (0, 5, 10 and 15%) of maize bran as additive.

The ensiling was done by filling the chopped grass materials in the ensiling plastic bag silos with 30 nanometer (nm) thicknesses. Air was squeezed out and the neck of the bag was twisted, turned over and tied with a rubber band. Each bag was then inserted into a second empty shopping plastic bag (30 nm) which was also tied, labeled and put in a hessian bag to protect it from rupturing. Hessian bags were then stored in a thatched barn. Thatched barn is cheaper and affordable when compared with an earth-pit (Lyimo 2010). In the thatched barn, the hessian bags were carefully stacked on a wooden rack to allow ventilation and lower the temperature. Chicken wire mesh surrounded the wooden rack protecting the bags against rats, mice and birds, especially the crow who would view the bags as bin bags full of kitchen waste to consume.

Data collection procedures

After 60 days of fermentation, the plastic bag silos were opened, and spoiled silage was separated from well preserved silage. Samples (weighing 500 g) from each bag were collected placed in polythene bags and immediately placed in a cool ice box and taken to the analytical laboratory. The sample was sub-divided into two samples. One sample was used for organoleptic test and pH determination. The other sub-samples were put in plastic bags and stored in a deep freezer at -10°C until they were used for chemical analysis and determination of IVDMD. The DM contents of the fresh ensiling material and silages were determined by drying in an oven at 65°C for 48 h ( AOAC 1984). The silages were freeze-dried in a Lyophilizer maintained at - 40 ºC for 24 h according to Snowman (1988), so as to get a dry sample for ash, crude protein (CP), water soluble carbohydrates (WSC) analysis and IVDMD determination. Ammonia-nitrogen was analyzed in fresh silage samples. The ash, CP and NH₃N were analyzed according to AOAC (2005) procedures while WSC was analyzed according to Thomas (1977). A pH meter (model 219-MK 2; PyeUnicam) was used to measure the pH of the fresh silage samples. Samples of 40 mg from each silo were soaked in 200 ml of cool distilled water for 12 hours then filtered and the supernatant used for the determination of the pH. The IVDMD of each of the silages was determined according to the two stage technique developed by Tilley and Terry (1963) and modified by Salabi et al (2010). The silages were analyzed for volatile fatty acids according to Shirlaw‘s (1967) proce­dure. Gas Chromatograph analyses were performed on a wide bore fused silica Cp-sil 19CB column, gas chromatograph equipped with a flame ionization detector (FID) 512x10^-12Afs. The technique used a gas chromatograph capillary column (10 m, 0.53 mm fused silica WCOT Cp-Sil 19CB (2.0 μm Cat.no.7647). The injector and detector temperatures were 275°C and 300°C respectively. The carrier gas was H₂ 40kPa (0.4bar) 170 cm/s. The analyses were performed using a temperature programme: a linear gradient from 80°C to 280°C at 25°C min^-1. In each case a 0.1μL of sample was injected (a flow splitting 1:10). Silage stability was determined by observing the change of pH of exposed silage after sixty days of fermentation. Each day the pH of each treatment was recorded for 7 days consecutively.

Organoleptic test

The organoleptic test was carried out at the Department of Animal, Aquaculture and Range Sciences laboratory of SUA by trained 30 assessors of Animal Science Undergraduate and Postgraduate Students. Each assessor assessed the silage from each treatment and scored its physical characteristics in terms of appearance, texture and smell. Appearance score No.1 (poor) indicated spoiled silage which was dark brown in color with mold growth, score No. 2 (moderate) olive green in colour with some mold growth, score No. 3 (good) light yellow or green brown colour and score No.4 (very good) indicated well pickled light green/yellowish green colour silage. Smell score No.1 (poor) indicated foul smell associated with putrefaction or tobacco-like smell, score No. 2 (moderate) pungent smell of ammonia, score No. 3 (good) pleasant ester aroma and score No.4 (very good) pleasant aroma typically silage smell. Texture score, No.1 (poor) slimy and watery, score No. 2 (moderate) firm, less slimy and wet No.3 (good) moderate firm, non-slippery and wet No.4 (very good) very firm, non-slippery and slightly wet. The test was carried out once after 60 days of fermentation, when ensiling bags (silos) were opened and spoiled silage separated from well preserved silage.

Data analysis

The General Linear Model (GLM) procedure of Statistical Analysis System (2008) used to analyze the data was based on the following statistical model: Y_ijklm = µ+W_i + C_j + A_k+(WC)_ij + (WA)_ik + (CA)_jk + E_{ijklm ;} whereby Y_ijklm= observation from the m^th sample drawn from the l^th replication within the k^th additive level, j^th chopping length and i ^th wilting method; µ = general mean common to all observations in the experiment; W_i = effect of the i ^th wilting method; C_j = effect of the j^th chop length; A_k =effect of the k^th additive level; (WC)_ij, (WA)_ik and CA)_jk are interaction effects of the factors indicated by the corresponding symbols; E _ijklm= random effects peculiar to each observation in the experiment.

Results and discussion

Chemical composition and digestibility of elephant grass and maize bran at the time of ensiling

Maize bran had relatively higher DM, CP, WSC and IVDMD but lower ash than elephant grass (Table 1).

Effect of wilting, chopping lengths and different levels of maize bran on grass silage organoleptic tests

Better appearance, smell and texture scores in wilted grass silage than in un-wilted grass silage (Table 2), might have been due to reduced moisture which provided favorable conditions to fermenting microbes resulting in good physical scoring. Better sensory scores in silages produced from 2 cm chopping length than in those from 4 cm chopping length could be due to greater packing density and thus excluding air from the silage which resulted in good conditions for fermentation. The results were in consistence with those reported by O’Kiely (2001), who recommended 1-2 cm chopping length to achieve good fermentation.

Silages treated with maize bran at 10% level had better sensory scores than silages treated with maize bran at other levels (Table 3).

Effect of wilting, chopping lengths and different levels of maize bran on chemical composition of grass silage

Wilted silage had higher DM, CP, WSC and ash but lower IVDMD than un-wilted silages (Table 4). According to Keady (1998), wilting reduces silage digestibility due to loss of available nutrients and an increase in ash concentration.

Two cm chopping silages had higher DM, CP, WSC and IVDMD than 4 cm chopping length (Table 4). High DM could be due to greater packing density and thus exclusion of air in 2 cm than in 4 cm chopped silage. The results are in agreement with Piltz and Kaiser (2004) who stated that, short chop length reduces degradation of the protein fraction. High WSC was probably due to thorough compaction and thus expulsion of air and this stopped the aerobic process and then WSC remains as recovery substrate. These results agree with Mushi et al (2000) that chopping of forages prior to ensiling restricts losses due to aerobic deterioration because of thorough compaction and thus expulsion of air.

Silages treated with maize bran at 10 and 15% level had higher DM, WSC and ash than the other levels (Table 5). Higher DM was probably due to ability of maize bran at 10 and 15% level to absorb moisture from silage than maize bran at 0 and 5% levels. Good results have been obtained with maize bran at 10% level as reported by Lyimo (2010). On the other hand, silages treated with maize bran at 10% level had higher CP and IVDMD than level 0, 5 and 15%. The increased CP could be due to protein sparing activity and pH has been reduced sufficiently to inactivate the plant proteolytic enzymes. Leibensperger and Pitt (1988) pointed out that a rapid decrease in pH inhibits clostridial fermentation and hydrolysis of plant proteins by plant enzymes.

Effect of wilting, chopping lengths and different levels of maize bran on fermentative quality of grass silages

Wilted silage had higher lactic and acetic acid and higher pH but lower NH _3-N and butyric acid than un-wilted grass silage (Table 6). The high proportion of lactic and acetic acids indicates the dominance of lactic acid bacteria. High pH could be attributed to the lower water activity of the wilted herbage (Greenhill 1964) which would have created more inhibitory conditions for microbial fermentation. These findings concur with Keles et al (2009), who found higher pH in wilted grasses. The lower NH₃N in wilted grasses indicated less proteolysis in wilted grass silage than in un-wilted grass silage. Higher lactic and acetic acids but lower pH, NH₃N and butyric acid in 2 cm chopped than in 4 cm chopped silage could be attributed to greater packing density in 2 cm chopped silage 2 cm and thus exclusion of air which resulted to rapid pH drop leading to high lactic production. According to Piltz and Kaiser (2004), short length increases amount of lactic acid produced in wilted silages. Neumann et al (2007) found that small sized particles provide greater compression efficiency and consequently reduces pH. A rapid decrease in pH inhibits clostridia fermentation and hydrolysis of plant proteins by plant enzymes (Leibensperger and Piltz 1988).

The observed higher lactic and acetic acids but lower pH, NH₃N and butyric acids in silages mixed with maize bran at 10% than maize bran at 0, 5 and 15% could be due to optimal additional energy supplied by the additives that created more conducive environment for the anaerobic fermentation bacteria (Table 7). This is in agreement with‘t Mannetje (2000) who reported that additional energy supplied by the additives provided good environment for anaerobic bacteria.

Effect of wilting, chopping lengths and different levels of maize bran on stability of grass silages

The results indicated that, wilted grass silages were more stable than un-wilted grass silages (Figure 1). Stability is ability of maintaining pH less than five for long period.

Wilted grass silages maintained pH less than five up to the third day of feeding out whereas un-wilted grass silages had pH greater than five from day 0. This implies that, wilting has an influence on the stability of grass silages. Wilting produces stable silages and’ the higher the stability, the higher the quality’. This is consistence with other studies like that of Mtengeti et al (2006) who found high quality silage after wilting.

Figure 1. Effect of wilting on stability of grass silage

Silages from 2 cm chopping were more stable than those with 4 cm chopping (Figure 2). They maintained the pH less than 5.0 up to the third day of feeding out while those from 4 cm chopping maintained the pH less than five only up to the second day. This could be attributed to greater packing density in 2 cm chop and thus exclusion of air in the silage than for 4 cm chop. This resulted into a rapid pH drop leading to high lactic acid production which inhibits clostridia bacteria and thus prolonged silage stability. This is supported by Coetzee (2000) who noted that a basic principle of ensiling is to provide adequate compaction of the crop to minimize air infiltration.

Figure 2. Effect of chopping length on stability of grass silages

The results in Figure 3 illustrate that silages with 10% maize bran were more stable than those with maize bran at 0%, 5% and 15% levels. This observation was similar to that observed by Jaurena and Pichard (2001), who reported an influence of additives on the stability of silage during the feeding out.

Figure 3. Effect of maize bran level on stability of grass silages

Conclusion

Silages produced from wilted elephant grass, chopped to 2 cm and treated with 10% maize bran had better appearance, smell, texture scores, DM, CP, WSC, lactic acid, acetic acid and stability but lower NH₃N and butyric acid than those from un-wilted elephant grass, chopped to 4 cm and treated with either 0, 5 or 15% maize bran levels.

Acknowledgements

The authors extend their sincere thanks to staff members of the Department of Animal, Aquaculture and Range Sciences, for their technical assistance and Magadu Dairy farm of Sokoine University of Agriculture for their assistance in silage making, storing and sampling.

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Received 21 February 2018; Accepted 16 May 2018; Published 1 June 2018

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