| Livestock Research for Rural Development 35 (8) 2023 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Desho (Pennisetum glaucifolium) grass is an improved multi-purpose indigenous forage palatable for cattle, used for soil conservation, drought tolerant, and widely adaptable in different agroecologies of Ethiopia. This study was conducted to assess the effect of harvest height and additives on forage quality, preference, and digestibility of silages made from desho grass. The study was designed as a three-by-four factorial arrangement with three replicates in Assosa, Ethiopia in 2019. The grass was harvested at three heights (HH-70, HH-90, and HH-110 cm), and four additives types (untreated (WO), treated with 4% molasses (WM), 0.6% urea (WU), and 0.6% urea + 4% molasses (WUM)). In addition to this by selecting HH-90 with four additives, silages were prepared in the same way for preference and digestibility studies. Desho grass with molasses-based (WM and WUM) silages had a moderate smell score (one to four) compared to WO and WU silages. The HH-90 and HH-110 had good fermentation. As compared to WM higher pH value was recorded for silage-treated WU and followed by WO. The greatest CP content was at HH-90 and silage treated with molasses-based additives. The preference study indicates that the highest dry matter intake was observed for silage with WM while WU resulted in the least intake by Arab goats (Capra hircus). The additives showed higher CP digestibility than the WO silage. The study indicates that desho grass harvested at 90 cm height at harvest and ensiled with molasses is optimum for silage conservation practice.
Keywords: Arab goats, desho grass, height at harvest, silage
The major feed-related problems globally, including in Ethiopia that are hindering livestock productivity include seasonal variation in the availability of green feeds, the poor nutritional quality of feed, unaffordability of concentrate feed, and less adoption of forage preservation techniques like hay and silage-making (Abebe et al 2017).
In Ethiopia, forage preservation hay and silage are less adopted. In the country, feed shortage is mainly caused by a lack of knowledge of feed conservation practices (Solomon et al 2014). Native pastures deteriorate rapidly during the dry season causing a critical feed shortage during those periods when the communities practice burning pasture lands and bushes in the region.
To alleviate the problem of feed shortage, the production and preservation of improved forage species have tremendous potential. However, in western Ethiopia, high precipitation during the rainy season is a major problem to preserve hay. One management approach to avoid this problem is ensiling surplus forage during the rainy season (Tripathi et al 1995).
To prepare quality silage, the first and the most important condition is the maturity of grass at the harvesting stage because the low dry matter (DM) and water-soluble carbohydrate (WSC) contents result in poor fermentation of freshly cut material (Carvalho et al 2017). Consequently, after wilting to attain appropriate pre-ensiling moisture, to increase the silage quality and nutritive value, additives are important (Zou et al 2021). Additives like fermentation-stimulating carbohydrate sources (e.g., molasses, cereals, beet, and citrus pulp) serve as an energy source for lactic acid bacteria (Yitbarek and Tamir 2014). Molasses is one of the most widely used additives to provide fast fermentable carbohydrates for the ensilage of tropical herbages (Getabalew et al 2022). Chemical treatment, such as urea treatment, is also considered effective to improve the nutritive value and nutrient digestibility of feed (Rusdy 2022). Urea is an interesting alternative nitrogen (N) source to anhydrous ammonia in the treatment of lignocellulose feedstuff due to its low cost, easy handling, and low danger in handling (Ahmed et al 2013).
Desho grass (Pennisetum glaucifolium)is an improved, palatable species to cattle and goats, highly popular indigenous, perennial, drought tolerant, multipurpose forage with low management inputs. In Ethiopia, the grass is widely adapted across ecological environments, and with which smallholder farmers are familiar with desho grass as a major feed for ruminants (Abera et al 2021; Asmare et al 2016; Yakob et al 2015). The desho grass is planted using vegetative root splits and annually produces 11.49 - 39.7 t/ha of dry matter (DM) yield (Atumo 2022). Due to its rapid growth rate, the grass is good for multi-cut harvesting and is readily consumed by ruminants (Asmare et al 2016). In addition to livestock feed, desho grass is used for soil conservation practices in the highlands of Ethiopia (Yakob et al 2015). The grass requires a permanent plot inaccessible to free-grazing livestock. It is utilized as a cut-and-carry and provides monthly cuts during the rainy season (Danano, 2007). Desho grass can attain the first harvest between 4-5 months after planting and reaches a height of 50-60 cm. But another report also showed that the height of desho grass ranges from 90-120 cm within the first five months depending on the type and fertility of the soil (Leta et al 2013).
Field observation on desho grass at Assosa Agricultural Research Center showed that growth behavior indicates continuous if moisture is available in the soil without transition and reproductive stages development at a certain time of growth. A study by Solomon et al (2017) shows that desho grass heading is sporadic and sterility is an apparent characteristic. Therefore, it is difficult to differentiate the grass harvesting timing by developmental stages like the initiation of flowers, 50% flowering, and maturity to harvest and feed for livestock. Currently, due to the above problem, this potential grass species is underutilized in western Ethiopia. So, utilizing height at harvest is a good option for desho grass to produce optimum DM yield and nutrient content, and to recommend a wider area of Ethiopia.
In Ethiopia in addition to feeding preservation free choice intake and acceptability study is very important to assess quickly the physical quality of the feed. Indigenous animals show a preference for feeds based on their nutrient content and avoid feeds containing plant secondary compounds, such as tannins (Provenza and Malechek, 1984). Therefore, studies are critical on this subject matter. Arab goat (Capra hircus) ecotypes are named after Arab/Berta tribe, the dominant tribe that generally owns these particular goat types. These goats are more adaptable to semi-arid areas, trypano tolerant, and considered a dual-purpose livestock animal (used for meat and milk production). Grass silage feeding is not common for the Arab goat. Studies showed that the voluntary feed intake of a goat is affected due to crop management, weather conditions, strong variations of the nutritional value, and fermentation quality of grass silage (Huhtanen et al 2002).
However, there is little information available concerning the optimum height at harvest of desho grass for silage production using urea and molasses as additives to improve silage quality, nutritive value, preference, and digestibility. Therefore, the objective of this study was to determine the effect of height at harvest and additives on silage quality, preference, feed intake and digestibility of desho grasses silages.
The desho grass establishment, silage making, preference, and digestibility experiments were conducted during 2019/2020 at Assosa Agricultural Research Center in Benishangul Gumuz Regional state Ethiopia (10°30’N, 034°20’E, 1565 masl). The long-term data (1966-2017) Gregorian Calendar (G.C) indicates the region precipitation pattern is uni-modal with a mean annual rainfall of 1146 mm, which falls mainly from May through December, and a mean annual temperature of 21.12°C, which varies from 16°C in December to 32°C in April (AMS 2008, Unpublished). Initial soil sample analysis shows the soil type in the experimental field was reddish-brown nitisols having a pH of 5.3, total N content of 0.24%, P content of 15.4 ppm, organic matter (OM) content of 2.42%, and cation exchange capacity (CEC) of 10.0 meq/100g soil in the surface 20 cm.
The Desho grass was planted on 19 July 2019. At the beginning of the experiment, the experimental area (402.5 m2) was prepared and divided into six blocks (11.5 x 5 m2) and three plots (3.5 m x 5 m) in each block with a total of 18 plots for laboratory silage making and chemical analysis of the silage. Six random plots from the 18 plots (one replicate in each block) were used for silage preparation at each height at harvest. Each height at harvests was assigned to each plot randomly by using the lottery method of randomization. The spacing was 1 m between blocks and 0.5 m between the plots. There were three treatments for height at harvest (HH) (70, 90, and 110 cm, designated HH-70, HH-90, and HH-110, respectively). Parallelly for the preference and digestibility studies, an additional 12 m x 36 m large plot was prepared in the same way to harvest desho grass at 90-HH.
Desho grass (Pennisetum glaucifolium, Kulumsa, DZF-592) variety was planted using two vegetative root splits per hole on well-prepared soil with spacing between the plant and rows of 25 and 50 cm, respectively (Worku et al 2017). Fertilizer was broadcast at planting time (100 kg/ha 18-46-00, N and P) and 21 days after planting (25 kg/ha 46-00-00, N). Weeding and related management practices were applied according to the recommended management practices (Leta et al 2013).
Desho grass harvesting stage was determined by measuring the height of the grass through continuous monitoring of each height at harvest. To determine the height at harvest, the sample measurements were taken from different places of each plot and the average height was taken for harvesting. The plant height was determined by taking the height of five plants per plot from the ground level to the natural standing height. The grass was harvested from individual plots, leaving an 8 cm stubble (Asmare et al 2017), and chopped manually using a machete to about 2-3 cm and allowed to wilt for 24 hours targeted to DM of 30-35% (Hadgu et al 2015). Harvesting took place on 02 November 2019, 28 November 2019, and 23 December 2019 for the HH-70, HH-90, and HH-110 treatments respectively.
A fresh herbage yield of the grass was measured immediately after each harvest and weighed on the field using a field balance. Representative subsamples of 300 g fresh chopped and thoroughly mixed desho grass were collected from each plot, and dried through a Forced Air Drying Oven (BOV-T50F, Biobase, Shandog, China) at 65oC for 72 hrs and reweighed to determine DM content, and then milled through a 1 mm screen, and stored in airtight plastic bags for grass chemical analysis to be described.
The laboratory experiment to assess silage quality was a 3 (HH, as described) x 4 (AD) factorial arrangement with 3 replications. The silage additives were without additives (WO), with 4% molasses (WM), 0.6% urea (fertilizer grade, 46% N) (WU), and both 0.6% urea + 4% molasses (WUM) in a completely randomized design (Yunus et al 2000). A 10-kg capacity plastic bag was used in three replicate of the HH-AD treatment combination, making a total of 36 plastic bag silages. The weight of the wilted grass was taken first and the required amount of additives was measured based on the wilted weight basis of the ensiled chopped grass. For each replicate bag, 5 kg of the sample was weighed and treated with the respective AD treatment as a weighted % of the wilted grass. To avoid viscosity, molasses was diluted with warm tap water. Urea was also dissolved with warm tap water at a ratio of 1:1 for uniform. When WU or WUM were applied, the amount of warm tap water used for dilution equals the amount of molasses used by weight. For WUM, molasses was diluted first and urea was added to it and mixed thoroughly. Then the chopped grass was placed on a polyethylene sheet laid on a concrete floor, sprinkled with the respective AD treatment, and thoroughly mixed. Then the chopped grasses were filled into their plastic bag layer by layer, compacted, and pressed with a wooden stick, and immediately, the bags were tied carefully with rope and placed under ambient temperature in a room. After 21 days of ensiling, the bags were opened and subsamples from each bag were taken for the assessment of the physical quality, chemical composition, and fermentation characteristics of silages.
For this study due to difficulties to manage all 12 desho silage types in the feeding experiment only the HH-90 height at harvest was selected based on the previous study in which the desho grass shows optimum DM yield and nutrient content (Asmare et al. 2016). The four AD treatments have the same percentage as those previously described but use 350 kg capacity plastic bags for each treatment.
The observation of mold formation and extent was done during the opening of the silos. After observation of the mold, by removing the top part of the silages, several hand grab samples from the middle part of each bag were mixed thoroughly and triplicate subsamples (from each) were taken. The sample one was used for fermentative quality evaluation, one for physical characteristics assessment and one for chemical analysis.
For physical characteristics determination, the scores 1 to 4 in a bad, moderate, good and excellent respectively of smell, color, texture and moldiness were used in the statistical analysis.
For pH determination, about 20 g of silage sample per bag was placed in a beaker to which 100 ml of distilled water was added (Australian Fodder Industry Association Inc. 2003). The samples were blended using a glass stirrer manually for thirty minutes and then kept for one hour and filtered through a cheesecloth. Then silage pH was measured from the extract using a calibrated digital pH meter (PH-016, Graigar, China). The pH meter was calibrated with buffer solutions of pH 4, 7, and 9.
About 500g of fresh silage subsamples were taken from each bag for chemical analyses. The DM content of silage was determined by drying the samples at 65°C in a Forced Air Drying Oven (BOV-T50F, Biobase, Shandog, China) until a constant mass was achieved (AOAC 1990). After drying, the samples were ground through a 1 mm cross-beater mill (Thomas-Wiley, Philadelphia, USA) for chemical analyses. The total N content was determined by the Kjeldahl method using an Auto Kjeldahl System (Buchi, Flawil, Switzerland) (AOAC 1990) and then the CP content was calculated as N x 6.25. The Ash content was determined by complete burning in a muffle furnace at 6000C for 3 hours (AOAC 1990). The Neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were analyzed by Fibertec® ( M 1020 Hot Extractor and 1021 Cold Extraction, Fibertec, Tecator, Hoganiis, Sweden) according to the procedure described by Van Soest and Robertson (1985).
Four 26-month-old intact male Arab goats with an initial body weight of 25.32 ± 0.84 kg were selected from the Assosa Agricultural Research Center goat farm for the preference experiment of HH-90 desho grass silage using the AD treatments previously described. The experiment was conducted for a total period of 23 days consisting of a 15-day adaptation period to the experimental feed and pens followed by eight days of preference study. During the adaptation period, animals have vaccinated with lyophilized virus vaccine PPR virus strain cultured on VERO – cells 1 ml diluted in 100 ml of cool and sterile saline water for peste des petits ruminants (PPR) through subcutaneous injection at mid-neck region (NVI, Bishoftu, Ethiopia). And for the prevention of external parasite 1.6 liters of acarmic used for every 800 litter of water and sprayed them using a knapsack sprayer (Amitraz 12.5%, Canelones, Uruguay). Moreover, the goats were dewormed with 1 bolus for 250 kg body weight broad spectrum Albendazole 2500 mg (Albentong 2500, China), using a balling gun, against internal parasite as prescribed by the manufacturer. The preference experiment was conducted in a room divided into four pens (replicates). Four feeding troughs (plastic boxes) were provided for each pen and each AD silage was added ad libitum (≈20% refusal) within each pen so that each goat had free access to all four silages. A cafeteria feeding approach was used, permitting ad libitum access to the silage of their choice (Larbi et al 1993). Additional silage was provided whenever the amount fell below 100 g. No other feed was provided during the preference study. The positions of the troughs were randomized each day to avoid the habit reflex (Brown et al 2016). Water and mineral licks (common salt) were provided ad libitum.
The weight of the silages was determined 10 hours after the offer (8 am) to calculate the total DM intake. Silage offered and refused per goat was weighed and recorded daily to determine as-fed intake by each animal for each silage. Representative samples of the offered silages were taken daily and dried at 105oC to determine the daily intake of DM for each animal. Finally, the DM intake data were used to determine the relative preference of the silage. The relative preference index (RPI) was calculated by dividing the intake of each silage by the total intake of the most consumed silage and the results obtained were then multiplied by 100 (Larbi et al 1993). The silages were ranked based on the percentage of preference (Olorunnisomo and Fayomi 2012).
Twenty 23-month-old intact male Arab goats with an initial body weight of 24.46 ± 1.05 kg were selected from the Assosa Agricultural Research Center goat farm for the apparent digestibility comparison of desho grass silages. Each pen was equipped with feeding and watering troughs. The goats were individually housed in a well-ventilated and roofed pen. The pen was cleaned once a day early in the morning. During the adaptation period, animals were treated for disease and parasites as previously described in the preference study. Access to water and common salt licks also was provided throughout the study as described.
The four AD treatments previously described were evaluated using five randomized complete blocks, each consisting of four goats based on initial live weight. Goats within a block were randomly assigned to one of the four AD treatments. The experimental animals were adapted to the AD treatment feeds for two-week. The feed was offered twice daily at 8 am and 4 pm. Silage was provided to all animals ad libitum by adding a 15% allowance of the previous day’s intake. No other feed was provided during the entire digestibility experiment.
After twelve days of adaptation to the silages and three days of adaptation to carrying the fecal collection bag, daily feed offered, refused and total fecal output by each goat were weighed and recorded for seven consecutive days at 7:30 am. The total amount of feces voided was collected and weighed every morning before feeding and stored at a temperature of -20oC in the medical freezer (MDF-235, Sanyo, Japan). On the last day of the collection period, fecal samples were thawed, and thoroughly mixed, and 20% was subsampled from a fecal composite sample for each animal. This subsampled was dried at 60oC for 72 hours and ground to pass through a 1-mm sieve screen and stored in a plastic bag pending chemical analysis as previously described. Finally, the digestibility of each DM and nutrient was calculated using the following equation (Cho,1979).
|
The data were subjected to analysis of variance using the General Linear Model (GLM) of the R version (R4.0.0). Treatment means showing significant differences at the probability level of p<0.05 were compared using Duncan’s new multiple range test (DNMRT).
Daily RPI values obtained for each treatment were subjected to analysis of variance with feeds as treatment and individual animals as replicates in a completely randomized design.
The statistical model for DM yield and chemical composition as affected by the height at harvest was analyzed:
Y ijk = µ+ H i + ε ijk
Where Y ijk is the response (yield and chemical composition of desho grass) at each height at harvest
µ =overall mean
Hi= effect of height at harvest (HH-70, HH-90, and HH-110),
ε ijk = the residual error.
Response (silage physical, fermentative and chemical composition) as affected by height at harvest and additives
Y ijk = µ + H i + A j + HA ij+ eijkWhere; Y ijk is the response variable, µ is the overall mean, H i is the fixed effect of harvesting height, i= 70, 90 and 110cm; A j is the fixed effect of additives, j= additives; HA ij is the interaction of harvesting height i and silage additive j and eijk is a random error.
Apparent digestibility trials include diet and error effects
Y ij = μ + t i + b j + eijk, Where, Y ij = is the response variable μ= is the overall mean, ti= is the treatment effect b j =is the block effect and e ijk is the random error.
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Table 1. The nutrient composition of desho grass at different heights at harvest. Values are the means of three replicates (% DM basis). |
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|
Parameters |
Desho grass |
p-value |
||
|
HH (cm) |
||||
|
70 |
90 |
110 |
||
|
DMY (ton ha-1) |
9.66+1.17 c |
13.33+1.16 b |
19.60+0.67 a |
<0.001 |
|
DM |
24.10+0.57c |
26.10+0.20b |
30.82+0.68a |
<0.001 |
|
CP |
10.77+0.16a |
9.63+0.17b |
6.13+0.05c |
<0.001 |
|
Ash |
7.69+0.16a |
5.38+0.13b |
5.38+0.09b |
<0.001 |
|
NDF |
57.24+1.99 c |
60.45+0.60 b |
64.92+1.91 a |
0.01 |
|
ADF |
38.52+0.40 c |
45.53+0.36 b |
48.01+0.89 a |
<0.001 |
|
ADL |
8.82+0.13 b |
10.11+0.26 a |
10.39+0.13 a |
<0.001 |
|
Treatments mean with different letters in a row are
significantly different (p < 0.05), |
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The chemical compositions of desho grass harvested at different heights before ensiling are indicated in Table 1. The desho grass DM yield per hectare highly increases from HH-70 to HH-110. The previous study shows that the optimum DM content of ensiled forage is between 30-35% (Xiccato et al 1994). In our study, only the DM content of desho grass at HH-110 cm was within this limit. The mean CP content of desho grass obtained from the current experiment was within the range of 5.9-13.8% reported for Pennisetum species (Kahindi et al 2007). In the present study, the mean value of CP shows 8.84%, and this value is slightly higher than a study by Asmare et al (2017) who reported a mean value of 8.35% CP content with the cutting heights of desho at 71, 94, and 106 cm in Ethiopia. The fiber content of desho grass increased with the increase of HH. There was an increase in NDF, ADF, and ADL contents. This result is in line with Asmare et al (2016) who reported that desho grass height is negatively correlated with CP content (0.07) but higher positive correlation with NDF and ADF content (0.40 and 0.60 correlation coefficient, respectively).
The effect of HH, AD and their interaction on the average score values of desho grass silages is presented in Table 2. There was no consistent trend concerning plant height on smell because HH-70 and HH-110 had similar scores but were better than HH-90. The result showed molasses-based additives (WM and WUM) were a moderate (p<0.05) smell than the WO and WU which shows a bad smell. The molasses-based additives resulted in silage with a better texture compared to the control and with urea only. This lower smell score in these silages may be linked with the rise of pH which caused the growth of clostridia bacteria in the silage. These organisms produce butyric acid, which smells like rancid butter (Kalač 2011). The present study indicates the color of the silages was no different between additives-based and WO. The result further indicates when desho grass height at harvest increases, the silage color shows an improvement. Generally, the result showed the physical characteristics (color, texture, and moldiness) of desho silages improved as the height at harvest increased. This study is in agreement with previous studies by Khan et al (2012) who observed higher values for color, smell, and texture of silages at the later stage of harvesting than at the earlier stage.
The additive-based silage moldiness scores were higher and better (p<0.05) than the WO scores. This may be related to the higher concentration of lactic acid that inhibits the proliferation of microorganisms in the additive based than in the untreated silage (Abebay et al, 2020). The result based on height at harvest showed moldiness score at HH-110 was greater (p<0.05) than that of HH-70.
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Table 2. The main effect means and results of statistical analyses for physio-chemical properties of desho grass silage at different heights at harvest (HH) and additives (AD) at Assoso, Ethiopia in 2019 |
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|
HHa |
Physio-chemical property |
||||||
|
Smell |
Color |
Texture |
Moldiness |
pH |
|||
|
WO |
1.00b |
2.89 |
2.78b |
2.67b |
5.01b |
||
|
WM |
2.11a |
2.67 |
3.67a |
3.33a |
4.21d |
||
|
WU |
1.00b |
3.00 |
2.78b |
3.55a |
5.34a |
||
|
WUM |
2.00a |
2.89 |
3.44a |
3.55a |
4.74c |
||
|
AD |
|||||||
|
HH-70 |
1.58a |
1.92b |
1.92c |
3.00 b |
5.06 a |
||
|
HH-90 |
1.25 b |
3.17 a |
3.58 b |
3.25 ab |
4.66 b |
||
|
HH-110 |
1.75 a |
3.50 a |
4.00 a |
3.58 a |
4.75 b |
||
|
SEM |
0.16 |
0.3 |
0.19 |
0.25 |
0.10 |
||
|
p-values |
|||||||
|
HH |
0.001 |
<.001 |
<.001 |
0.010 |
<.001 |
||
|
AD |
<.001 |
0.600 |
<.001 |
0.001 |
<.001 |
||
|
HH × AD |
<.001 |
0.008 |
<.001 |
0.220 |
<.001 |
||
|
Means within a variable and column followed by similar letters are not significantly different based on the 5% Duncan’s new multiple range test. Values are the means of three replicates and either four AD treatments for HH treatments or three HH treatments for AD treatments, WO= without additives; WM = with 4% molasses; WU = with 0.6% urea; WUM = with 0.6%urea + 4% molasses; HH-70, HH-90, and HH-110 = height at harvest (cm); SEM = standard error of the mean, Quality scoring for each variable, except pH: 1- bad; 2-moderate; 3-good; 4-excellent. |
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The result showed the highest (p<0.05) pH score was recorded for silage treated with WU followed by WO silage. As compared to the other additives WM lowers the pH and improves the fermentation quality of desho grass silages. The silages were poorly fermented at HH-70. But HH-90 height at harvest is lower in pH and shows good fermentation. Kung and Shaver (2004) stated that good quality grass and legume silage pH values in the tropics range between 4.3 and 4.7. Except for silage with HH-70, the pH of silage in the current study is within this range. Silage made with WM and WUM gave silage within the pH range reported by Kung and Shaver (2004) suggesting that the silage with WM and WUM was good quality. The high pH value of desho grass WO in the current study shows that the WSC content maybe not be adequate for the fermentation of the grass. A sufficient amount of fermentable carbohydrates in plant material is necessary for lactic acid production, which reduces fermentation pH and guarantees good-quality silage (McDonald et al 2011). Silage treated with WU resulted in the highest pH, and the pH was lowered with the use of WM. Research result shows that adding urea is a common and cheap method of increasing N supply; however, urea decreases the fermentation quality of silage by increasing pH with the release of ammonia. Pancholy et al (1994) and Yunus et al (2000) stated that the quality of silage made from tropical herbages was generally of low fermentation quality as silage did not contain a large amount of lactic acid but considerable acetic acid.
Silage-made without additives (WO) had low DM content after ensiling than the molasses-based additives (Table 3). This implies that minor fermentation losses occurred ensiled with additives than the control. On the other hand, Getahun et al (2018) observed that additives did not affect the DM content of sugar cane top silage likely because of the much greater available WSC. The low CP content at HH-70 may be because, at higher moisture, clostridia may have developed and broken down protein and produced butyric acid, which will lower the palatability and intake of silage (Meeske et al 2002). It is well known that vegetative pastures have better nutritional quality than mature pastures, but they also have lower dry matter yield and high moisture content which may result in secondary fermentation, production of silage effluents, and spoilage of silage (McDonald et al 1991).
The greater CP content at HH-90 indicates that harvesting of desho grass at HH-90 height is the optimum height of harvest to ensile the grass. Molasses and a combination of molasses urea resulted in silage with higher CP content, which indicates that these additives preserve the silage well and maintain the nutrient content of the silages. The lower NDF content due to urea and a combination of urea and molasses in the current study indicates that urea or ammonia addition to silages increases the dissociation of crude fiber. therefore, crude fiber content decreases with ensilage (Huhtanen et al 2008) and NDF decreases (Islam et al 2001). Bolsen et al (1996) have shown that the addition of molasses to silages increases the number of anaerobic bacteria, including the lactic acid bacteria; therefore, the NDF and ADF degradation of silages increases. The silage ADF content increased when compared with the substrate crops, which may be caused by the loss of other components during the fermentation (Jaakkola et al 2006). Lignin content was not affected by the type of additives but was highest at the highest plant height, which could be associated with the stage of maturity of the grass. The study shows that ensiling did not affect lignin and ADF contents as lignin and cellulose are relatively stable for hydrolysis during silo fermentation.
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Table 3. Nutrient composition (% in DM basis) of desho grass silage at different heights at harvest (HH) and additives (AD) at Assosa, Ethiopia in 2019. |
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|
HH |
Nutrient composition (%) |
||||||
|
DM % |
CP |
Ash |
NDF |
ADF |
ADL |
||
|
WO |
24.65c |
6.69c |
7.62b |
61.70a |
45.50a |
8.08 |
|
|
WM |
26.30ab |
8.40a |
8.95a |
57.80b |
41.60b |
8.04 |
|
|
WU |
25.49bc |
7.38b |
8.92a |
54.09c |
41.30b |
8.19 |
|
|
WUM |
27.23a |
8.54a |
8.53a |
55.60c |
42.20b |
8.09 |
|
|
AD |
|||||||
|
HH-70 |
24.54b |
7.55b |
9.45a |
56.70b |
41.80b |
8.07b |
|
|
HH-90 |
25.16b |
8.26a |
7.54c |
57.20b |
41.50b |
7.90c |
|
|
HH-110 |
28.05a |
7.16b |
8.55b |
58.50a |
44.70a |
8.34a |
|
|
SEM |
0.81 |
0.26 |
0.3 |
0.59 |
0.17 |
0.08 |
|
|
p-values |
|||||||
|
HH |
<.001 |
<.001 |
<.001 |
<.001 |
<.001 |
<.001 |
|
|
AD |
<.001 |
<.001 |
<.001 |
<.001 |
<.001 |
0.34 |
|
|
HH x AD |
0.49 |
0.001 |
0.001 |
<.001 |
<.001 |
0.01 |
|
|
WO= without additives; WM = with 4% molasses; WU =
with 0.6% urea; WUM = with 0.6%urea + 4% molasses;
|
|||||||
The chemical composition of desho grass ensiled in a large plastic bag at HH-90 height at harvest treated with different additives is shown in Table 4. The DM and ash contents of the silage were no different (p>0.05) among treatments. The highest (p<0.05) CP content was recorded at WUM. The NDF and ADF contents were greater (p<0.05) in WO than in the other treatments.
|
Table 4. Chemical composition of desho grass (% DM) used for preference study and determination of apparent digestibility |
||||||
|
Constitute % |
AD |
SEM |
p-value |
|||
|
WO |
WM |
WU |
WUM |
|||
|
DM |
24.01 |
24.45 |
24.86 |
26.31 |
0.57 |
0.105 |
|
CP |
7.70c |
7.83c |
8.55b |
8.96a |
0.76 |
<0.001 |
|
Ash |
6.42 |
7.58 |
8.71 |
7.43 |
0.5 |
0.07 |
|
NDF |
60.70a |
56.70b |
55.10b |
56.20b |
0.86 |
0.008 |
|
ADF |
44.60a |
38.10c |
41.70b |
41.60b |
0.69 |
0.01 |
|
ADL |
8.00b |
7.73c |
8.14a |
7.73c |
0.44 |
<0.001 |
|
SEM= Standard error of the mean; WO= without additive; WM= 4% molasses; WU= 0.6% urea; WUM= 0.6% urea and 4% molasses,means with a common superscript letter within a row do not differ significantly (p>0.05) |
||||||
The relative preference index of silages in the current study showed that the use of molasses as an additive increased the preference for desho silages and hence had higher DM intake (Table 5). Jaakkola et al (2006) observed that DM intake was influenced by palatability, chemical composition, and physical attributes of the diet. Specifically, palatability is the property of a feed that affects its taste or smell as perceived by animals with particular experiences under specified conditions and goats' experience with the feed (McDonald et al 1991). The study by Bureenok et al (2012) indicated that the addition of molasses to Napier grass increased the intake of silage 1.4 times compared with silage-made without additives. The increase in silage intake may be explained by the higher residual WSC content in the silage treated with molasses (Murphy 1999). Desho grass silage with WO and WU additives was the least preferred and hence had the lowest DM intake. The fermentative and physical quality studies showed that silage prepared with WO and WU had an unpleasant smell and goats discriminated against these silages during the preference study. Study on cassava peel silage indicates dwarf goats reject the silages due to poor silage properties such as a pungent smell and moldy growth which could repel the animals (Falola et al, 2013). Moreover, this study indicates silage made from WO and WU treatments had low DM content compared to WM and WUM which may have created undesirable fermentation that reduces silage intake. Scherer (2019) indicated that high concentrations of biogenic amines in low DM silages may negatively affect DM intake. It seems that goats can detect subtle differences between silages and prefer forage based on small changes in plant chemistry that are difficult to detect in chemical analyses.
The high DM intake of silage made with WUM during the digestibility study is consistent with the study by Mustafa et al (2008) which they attributed to greater DM and CP contents, both of which are known to improve DM intake and growth rates in ruminants. The lesser silage DM intake of desho grass with WU might be due to some end‐products of fermentation such as acetic, butyric acids and ammonia (Kung and Shaver 2004). Poorly fermented silages have large concentrations of undesirable compounds that explain the low silage intake (de Oliveira et al 2016).
The better apparent digestibility of DM and OM with WUM treatment was consistent with a study by Huhtanen et al (2008) who showed that the use of urea and molasses affected digestibility positively. Bolsen et al. (1999) also show the addition of molasses to silages increases the number of anaerobic bacteria, including lactic acid bacteria, therefore, NDF and ADF degradation of silages increases. The increase in DM and OM digestibility for silages ensiled with urea and molasses are in line with the observed lower NDF content of this silage in the current study (Table 5). This may be expected due to differences in the N content of the silages and daily N intake by goats. The digestibility of NDF and ADF was the lowest for the control treatment compared to the additive-based treatment. Research has shown that the use of additives, main urea has increased the affinity of ammonia to water, which promotes the expansion and rupture of the cell wall components of tissues of forage treated with urea, this favors the partial solubilization of hemicellulose and influence increase in intake and digestibility of silage (Santos et al 2017).
|
Table 5. Preference and apparent digestibility of desho grass silage treated with different additives and fed to Arab goats |
||||||
|
Experiments |
Items |
Treatments |
SEM |
|||
|
WO |
WM |
WU |
WUM |
|||
|
Preference |
aDM intake (g/day/ goats) |
22.39c |
462.24a |
3.97c |
214.48b |
48.99 |
|
RPI (%) |
4.60c |
100.00a |
0.84c |
48.36b |
5.87 |
|
|
Apparent |
bDM intake (g/day) |
673.93b |
699.51b |
614.89b |
827.93a |
40.75 |
|
DMI/BW (%) |
2.58b |
2.72b |
2.38b |
3.27a |
0.14 |
|
|
Digestibility (%) |
||||||
|
DM |
60.36c |
67.53a |
64.91ab |
63.28bc |
0.95 |
|
|
OM |
61.38c |
68.77a |
66.03ab |
64.77b |
0.93 |
|
|
CP |
61.99c |
67.36b |
72.30a |
74.37a |
0.85 |
|
|
NDF |
55.29b |
63.97a |
65.10a |
64.33a |
1.02 |
|
|
ADF |
52.89c |
60.38b |
64.61a |
64.75a |
1.07 |
|
|
Means within a row with different superscripts are significantly different at p<0.05; ADF=acid detergent fiber; CP=crude protein; DM =dry matter; NDF=neutral detergent fiber; OM=organic matter; SEM=standard error of mean; WO= without additive; WM= 4% molasses; WU= 0.6% urea; WUM= 0.6% urea and 4% molasses, RPI=Relative Palatability Index aDM intake = cafeteria base of the four treatment DM intake per goat; bDM intake = DM intake per goat per-treatment |
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The authors have declared that no competing interests exist
This work was funded by the Ethiopian Institute of Agricultural Research. The authors thank the institute for its support in the study.
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