1. Introduction
Inadequate feed supply, in terms of quality, quantity, and seasonality, is a major constraint to ruminant production in sub-Saharan Africa [
1,
2]. In sub-Saharan Africa, the dominant feeding systems for sheep and goats are based on pastures and, in the aftermath, roadside grasses [
2,
3] and crop byproducts. They often contain less than the minimum content of metabolizable energy required for maintenance [
4]. As a result, animals suffer weight loss, lower birth weight, lower disease resistance, and invariably reduced reproductive and productive performance [
5]. Thus, there is an urgent need to use new research technologies to boost animal production. Improved feeding techniques include supplementation and the provision of improved forage and feed preservation, including ensiling. Feed preservation contributes to better feed quality, ensures longer shelf life, and maintains nutritional quality and palatability.
The two basic ways of forage preservation are hay and silage [
6]. Ensiling is a method of preserving wet season forage for use as animal feed during dry periods. Silage preparation is based on the anaerobic fermentation of water-soluble carbohydrates into organic acids, primarily lactic acid. The fermentation process stops at pH values below 4.2 and protects the moist forages from spoiling by germs [
7]. Silage processing is a potential option to ensure the supply of high-quality fodder in the event of feed scarcity [
8].
Cereal forages have different developmental stages, and the dough stage is the best harvest time for maximum yield and nutritive quality traits [
9,
10]. Harvesting
A.
sativa for silage at the dough stage increases the yield two-fold due to grain formation at the dough stage [
11]. Napier grass (
P.
purpureum) is a popular tropical grass for silage production due to its high biomass yield per unit area, high levels of water-soluble carbohydrates, its ability to withstand frequent cutting and rapid regeneration, tolerance to intermittent drought, and good palatability [
12,
13,
14]. It provides adequate digestible dry matter per hectare and supports a significant increase in weight per animal [
14].
Several researchers have reported that adding molasses to forage silage improves fermentation, dry matter, and lactic acid content while lowering pH and ammoniacal nitrogen concentration [
15,
16]. The addition of 4% molasses to
P.
purpureum grass silage has been found to affect fermentation parameters, crude protein, and structural carbohydrate breakdown [
15]. Harvesting
A.
sativa at the dough stage and
P.
purpureum at 60 days produces significant amounts of soluble carbohydrates. Despite the critical feed shortage and wide adoption of both
A.
sativa and
P.
purpureum forages in Ethiopia, little work has been conducted to evaluate the various preservation methods without compromising their quality. Furthermore, there is insufficient scientific information on the chemical composition, silage quality, and feeding benefits of combining
A.
sativa and
P.
purpureum with the inclusion of molasses to obtain more fermentable carbohydrates. Therefore, this study aimed to evaluate the fermentation characteristics and nutritive value of
A.
sativa genotypes ensiled either solely or in combination with equal parts of
P.
purpureum grass with the addition of 3% molasses as an additive for all treatments.
4. Discussion
One of the factors that affect the ensiling process is the DM content of the plant. It predicts the insolubility of forage crops [
38]. The DM content of the plants before ensiling range from 22.96% to 26.70% (
Table 2). After ensiling, the DM content ranges from 19% to 24% (
Table 5). The DM content is critical to producing good quality silage. There was up to 3.74% variability in the treatment values at the baseline and 3% variability at day 45. These variations are likely due to the differences in each
A.
sativa genotype used and the properties they exhibited when mixed with
P.
purpureum 16791.
The results of this study indicate that T6 probably had sufficient soluble sugar, which created an optimal environment for the successful fermentation by microorganisms. T6 had the lowest pH on the 45th day of fermentation, showing that this treatment had soluble carbohydrates that paved the way for fermentation by lactic acid bacteria. In addition, all treatments had a pH in the range of 3.52–5.01, indicating good preservation and in the range of good to average quality silage [
39]. A low pH (below 4) indicated high-quality silage [
15,
35]. The relatively highest pH value of 5.80 was measured for T3 (100%
A.
sativa ILRI_5526A ensiled with 3% molasses), indicating that this specific genotype had less soluble carbohydrates and a high buffering capacity as the ammonia delayed a drop in pH and increased DM loss [
40].
The silage treated with
A.
sativa ILRI_5526A (T3) had higher temperature values (
p < 0.0001) compared to the others, indicating that it was more susceptible to deterioration. This is probably due to the soluble carbohydrate content of the genotype and the creation of a less favorable environment for microbial fermentation compared to the others. A temperature of 25 °C was recorded for T6. This is an indicator of good silage where adequate fermentation has occurred [
41]. According to [
42], the temperature of the silage in small silos should be similar to the ambient temperature or a few degrees warmer. From this study, the amount of heat generated was low, indicating that little aerobic degradation occurred. The browning (Millard) reaction occurs when aerobic oxidation generates too much heat and creates a protein and carbohydrate combination that prevents protein and fiber digestion [
43].
These high temperatures are the result of aerobic bacteria oxidizing the extra air trapped in the forage mass. Importantly, these temperatures should drop quickly as more packaging forces air out of the mass and fermentation takes place. Heat-damaged protein can result from sustained high temperatures in excess of 45
–50 °C [
28]. Temperatures in the core of the silo typically drop gradually 25–30 °C once the active phase of fermentation is over. Big bale and bag silos are examples of small silos that are designed to cool faster than larger silos. Rarely, especially after several months of storage, is the temperature above 35 °C. Huge masses of fodder act as insulation in large silos, resulting in very slow heat dissipation and in core silage temperatures often remaining high for long periods of time [
28].
The total dry matter loss was lower (p < 0.0001) for silage made by ensiling 50% A. sativa ILRI_5527A + 50% P. purpureum 16791 with the addition of 3% Molasses (T6) compared to the others. A comparatively higher total dry matter loss of 2.67% was recorded for the treatment made by ensiling 50% chopped A. sativa ILRI_5526A + 50% chopped P. purpureum 16791 with the addition of 3% molasses (T7), suggesting that desirable microbes for quality silage are present in T6 compared to the others.
The ensiling of 50%
A.
sativa 5527A and 50%
P.
purpureum 16791 with the addition of 3% molasses (T6) resulted in a significant reduction in gas losses (
p < 0.0001). Secondary fermentation by entero bacteria, clostridium bacteria, and aerobic microorganisms causes gas losses in silage. These microbes typically thrive in poorly fermented silage, while well-fermented silage with high levels of lactic acid fermentation produces minimal nutrient content [
28]. This happens when the sugar content is particularly high. Yeast development leads to alcohol fermentation, which leads to gas losses in the form of ethanol. According to [
41], moisture loss through the stomata peaks soon after cutting and stops within 2 h as a result of complete stomata closure. However, moisture loss through the cuticle can still occur after that.
Effluent production was lower for T6 than for the others. Abundant effluent production in silage results in high losses of organic substances such as sugars, organic acids, and proteins [
36]. The absence of organic substrates reduces the nutritional value of silage [
44]. Increasing the DM content in the silage by adding certain genotypes of the two forages (T6) led to a reduction in effluent production. Reduced effluent production refers to the reduction in nutrient losses due to percolation. Silage effluent is thought to transport nitrogen molecules, sugars, organic acids, and mineral salts [
41]. Effluent (or leachate) may be produced typically when the ensiled crop has a high moisture content [
45]. The moisture of pre-ensiled crop moisture can be influenced by plant factors [
41]. There is high variability in reported effluent production rates for different crops with different moisture contents [
45]. Fermenting a crop is said to lower the pH to inhibit putrefactive bacteria, thus preserving the protein content of the fodder [
41].
The mean odor score for T6 was higher (
p < 0.0001) than for the others. T6 treatment had a pleasant, sweet, and sour odor. A relatively lower odor score (
p < 0.0001) was recorded for T3. It was characterized as irritating, offensive, and acidic in odor, attributed to high ammonia production. A high concentration of ammonia indicates excessive protein breakdown during fermentation [
46]. According to [
43], good silage smells similar to milk due to the lactic acid content. The result of this study showed that T6 had a good forage quality at the beginning of ensiling, which is supported by [
6], which stated that the odor of the silage was influenced by the fresh forage.
According to [
47], good silage has a light green to yellow or brownish-green color, depending on the silage raw material. The mold coverage score of T6 was better (
p < 0.001) than the others. The lowest mold was absorbed by T6 compared to the rest of the treatments: a good quality score result. T6 had an excellent texture score (
p < 0.0001) characterized by a fluffy and soft texture. T6 had the best physical properties based on the parameters measured in this study.
Silage from T6 had the highest (
p < 0.0001) level of organic matter percentage and ether extract, whereas T3 had the lowest level of organic matter and ether extract. According to [
39], the nutrient content of the raw material and the microorganisms involved in fermentation influence the decrease in DM and OM contents during ensiling.
Silage made from sole
P.
purpureum (T4) had the highest (
p < 0.0001) crude protein content compared to the other treatments. Two of the treatments (T3 and T7) had the lowest crude protein levels. The crude protein content of all the treatment groups was above the minimum crude protein requirement of ruminants [
48]. The high nutrient content of T6 was likely due to enhanced microbial growth during the silage process, resulting in an increased microbial population. According to [
49], the microbes are single-cell protein sources that can increase the crude protein content in the silage.
The fiber fractions (NDF, ADF, and ADL content) of T1, T2, and T6 were comparable and lower (
p < 0.001) than the others. The lower proportion of NDF (<40%) makes these treatments a suitable feed resource for ruminants. A low fiber content improves nutrient utilization by animals [
50]. ADF and ADL levels critically affect feed quality. Research has shown a negative correlation between their high levels and the potential digestibility of a feed. As ADF increases, the feed becomes less digestible. This study showed that T6 had the lowest content of ADF and ADL. This has the potential to increase intake and digestibility by animals [
51]. According to [
50], heterofermentative bacteria convert simple glucose into organic acids (acetic, lactic, propionic, and butyric), which leads to a drop in fiber concentration. According to
Figure 1, T6 had the highest flieg point, followed by T4. The high flieg point record from T6 was attributed to the higher DM and lower pH of the silage. Measured by the flieg point, a DM, and pH-dependent value, all treated silages were in the range of medium to very good silage.
The selection of the cereal, A.
sativa, and the grass,
P.
purpureum, in this study is a good combination as it produces high-quality silage with little nutrient loss in 45 days. Legumes were excluded from this study because of their high buffering capacity, which reduces the quality of silage due to high CP and mineral contents which delay the drop in pH and increase nutrient loss [
52].
Forages with a high CP content, such as legumes, can be blended with low CP forages before or after ensiling in order to satisfy the ruminant’s need for CP. The problem is their low water-soluble carbohydrate (WSC) content, high buffering capacity, and substantial proteolysis during ensiling [
38,
53]. Due to legumes’ high buffering capacity, which negatively affects silage quality due to the plant’s crude protein and high mineral concentration, it takes a long time to drop the pH level and resulting in high nutrient losses [
52]. So far, different studies have been conducted using legumes for their potential as a crude protein (CP) source only. In this study, we used
P.
purpureum 16791, which had a relatively good source of protein with acceptable amounts of water-soluble carbohydrates). It yielded a high biomass per unit area.
A.
sativa was used in combination since it has technical characteristics that favor its use for silage making.
P.
purpureum 16791 has sufficient soluble carbohydrates with molasses to support or replace the deficiency. The study agrees with [
52] that any fodder, which has sufficient amounts of fermentable carbohydrates, can be ensiled.