Silage quality of forage maize (Zea mays L.) when ensiled in mixtures with molasses, Vigna unguiculata L. Walp or Moringa oleifera foliage

B Mendieta-Araica^1*, L Rocha¹, N Reyes-Sánchez¹, R Spörndly², M Jiménez¹, M Halling³, F Salmerón-Miranda⁴ and H Eckersten³

¹ Faculty of Animal Science, National Agrarian University, Managua, Nicaragua
* bryan.mendieta@ci.una.edu.ni
² Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala
³ Department of Crop Production Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden
⁴ Faculty of Agronomy, National Agrarian University, Managua, Nicaragua

Abstract

Feed availability and quality are the more pressing factors at tropical livestock systems, the use of concentrate feed is expensive, therefore other feeding options should be adopted, as it is the case of maize silage, while is well known worldwide and has many benefits, it also exhibits low content of crude protein. Along the time, the use of forage from shrubs, trees and local legumes has been an option to enrich the chemical composition of maize silage. The experimental aim was to evaluate five different silages, including VU ( Vigna unguiculata foliage plus molasses), ZM (Zea mays foliage plus molasses), MO (Moringa oleifera foliage plus molasses), ZMVU (Zea mays and Vigna unguiculata mixed foliage plus molasses) and ZMMO (Zea mays and Moringa oleifera mixed foliage plus molasses) under tropical conditions. A completely randomized design was set up with five treatments and three replicates each. Silage parameters were subjected to analysis of variance. Robust linear models were fitted to crude protein (CP), neutral detergent fiber (NDF), pH, Weight loss, Time to Spoilage (TTS) (using a biweight MM estimator) and ash (Huber weights). At Tukey test the effect sizes were significant when p< 0.05. The CP concentration was substantially increased in ZMVU and ZMMO. This study shows that the inclusion of Vigna or Moringa foliage has a positive influence in silage quality and In vitro dry matter digestibility (IVDMD); all pH values were considered optimal. Vigna foliage proved to be better in terms to preserve longer the silage after silo is open.

Keywords: aerobic stability, digestibility, ensilability, fermentation profile

Introduction

Tropical livestock is mainly based in grazing systems. However, due to seasonal cyclicality the biomass availability both in quantity and quality is very limited during many months of the year. This situation has been identified by many authors (Gómez et al 2019; Gutiérrez and Mendieta-Araica 2018) as on the major constrain in animal production systems. The use of concentrate feeds is not always an option because of its high price, and the use of imported components such as cereals, in many countries.

Silage making with available multipurpose feed resources is an interesting option to overcome the forage shortage during dry season. Maize has been widely used for this purpose in the tropics due to its high biomass yield, up to 12 ton dry matter ha^-1, (Asangla and Gohain 2016, Mutsamba et al 2019, Smith et al 2015) high carbohydrates contents, and its high nutrient digestibility (Gruber et al 2018; Guardia et al 2016). It is well documented that livestock need a good source of protein which is essential for rumen bacteria which digest the feed for ruminant animals (Fessenden et al 2019). However, a major shortcoming of using maize as unique resource in silage making is undoubtedly its low crude protein content (Baghdadi et al 2016). There is an urgent need for higher silage quality in tropical areas and new solutions using unconventional forage species is required. Different studies have reported that high quality silage could be made by mixing legumes or foliage trees during ensiling of forage (Aamir 2015; Mendieta-Araica et al 2011). Vigna unguiculata L. Walp (Vigna) is a nutritious fodder legume that has been used successfully to improve silage quality due to its high crude protein content ranging from 22 to 30% on a dry weight basis (Rao and Shahid 2011, Kermah et al 2017, El-Ghobashy et al 2018). In this sense, Contreras-Govea et al (2009) showed an increase in crude protein (CP) content as the proportion of Vigna increased in a maize silage mixture.

The potential of trees presents in agroforestry systems to supply animals with high quality feed has been widely reported. Among multiple tree species reported, Moringa oleifera (Moringa) is one of the most extensively species used for fodder (Kumar et al 2017). Positive effects of fresh and ensiled Moringa on lamb meat tenderness, dairy cattle performance, milk yield and nutrient digestibility has been reported by many authors (Mendieta-Araica et al 2011, Cohen-Zinder et al 2017a, Cohen-Zinder et al 2017b). Silage made of intercropped maize and Vigna has reported to produce a fodder improved in terms of dry matter (DM) and CP content (Prasanthi and Venkateswaralu 2014). Despite the aforementioned, the evidence of the silage quality is scarce when Maize, Vigna and Moringa are mixed. This study was conducted to evaluate silage quality of maize mixed with Vigna or Moringa foliage under tropical climate conditions.

Materials and methods

This experiment was carried out in the Feed Analysis Laboratory of the National Agrarian University (UNA) in Managua, Nicaragua. In the laboratory, the average relative humidity was 63 % and the average temperature was 30ºC.

Micro-silo preparation

Biomass used for micro-silo was obtained as separate materials harvested from irrigated and fertilized intercropped maize (cultivar NB6) with Vigna plots. Moringa foliage (leaves and branches of <five mm diameter) was harvested from non-irrigated pure stands at UNA. Sugar-cane molasses (molasses) was purchased from an agricultural feed supplier.

Maize was harvested by hand with a machete at the kernel dough stage of maize. Vigna was harvested at the same day as that of Maize at a vegetative stage in intercrop plots. Collected materials were counted, separated, weighed and weight proportion of Maize-Vigna was calculated on fresh matter (FM).

Moringa was cut 45 d after pruning. After cutting, edible fraction of Moringa forage was selected (which included leaves, petioles and stems of a diameter smaller than five mm) and were chopped into pieces of approximately two cm in length using a mechanical chopper.

Once the forages were chopped, five treatments were prepared using different proportions of Maize, Vigna, Moringa and sugar-cane molasses for ensiling.

Mixtures for each treatment were prepared and from these batches, fresh material was taken to fill in on average 1564 g fresh matter (FM) in glass jars with a nominal volume of 1800 mL. The fresh material was pressed into the jar to remove as much air as possible. The weight of the fresh material in each jar was calculated from the difference between empty and filled jars. The glass jars, subsequently referred to as micro-silos, were fitted with water-locks on their lids to let fermentation gases escape. Each of the five treatments had three replicates, giving a total of fifteen micro-silos. The temperature and relative humidity of the storeroom were registered three times daily. The water-locks were refilled when needed. Micro-silo weight was recorded every two days at 08:00 h.

All micro-silos were opened and analyzed 120 d after being closed. The contents from each micro-silo were transferred into plastic bags, thoroughly mixed and then samples sent for chemical analysis. The Ash and DM content was determined using AOAC (1990) using the drying method for determining DM in the fresh biomass and the toluene method for silage. CP content was determined using the Kjeldahl method (AOAC 1984).

To analyze pH, it was collected samples of approximately 25 g in which 100 mL water were added and after resting for two hours, the pH was read using a Thermo Scientific Orion 2-Star Benchtop pH meter. In another 25 g sample, 200 mL H₂SO ₄ 0.2 N solution were added and after a 48-hour rest, it was filtered through a Whatman 54 filter. This filtrate was stored in a refrigerator for later N-ammoniacal analysis (Bolsen et al 1992).

The concentration of neutral detergent fibre (NDF) and acid detergent fibre (ADF) was determined according to Van Soest et al (1991). The in vitro dry matter digestibility (IVDMD) and NH₃-N was determined according to AOAC (1990). The dry matter losses in the silages were quantified by weight difference and presented as Weight Loss in grams.

Aerobic stability phase

From each micro-silo, 250g sample was taken to evaluate aerobic stability using the modified method of Ashbell et al (1990). These samples were aerobically stored and protected by nets against insects. Both the sample and ambient temperature were measured during the deterioration process every two hours.

Once a sample temperature of five ºC above room temperature was recorded three times in a row, the silage sample was considered spoiled and sent for chemical analysis, the Time to Spoilage (TTS) was recorded in hours.

Experimental design and statistical analysis

A completely randomized design was set up with five treatments and three replicates (micro-silo) each. Silage parameters were subjected to analysis of variance. Inspection of residuals versus fitted values and normal probability plots were conducted to detect violation of model assumptions. Robust linear models were fitted to CP, NDF, pH (Fermentation profile), Weight loss, TTS (using a biweight MM estimator) and Ash (Huber weights). Multiple comparisons were conducted using the Tukey test and the effect sizes were significant when p< 0.05. The Spearman correlation between DM and pH was used to investigate the relationship between fermentation process and silage quality.

All the analyses were performed using R statistical software (R Core Team 2021).

Results

Chemical composition of silages

As can be seen, there was a wide range in DM content among treatments from 225 g kg ^-1 up to 362 g kg^-1. Inclusion either of Vigna or Moringa foliage significantly increases the CP content at maize silage. In fiber, NDF content of silages were among the range of 449 g kg-1 DM y 601 g kg-1 DM. A reduction in NDF (from 601 g kg ^-1 DM to 578 g kg ^-1 DM), and ADF (from 414 g kg-1 DM to 395 g kg-1 DM) was observed when 14.5% of Moringa foliage was added to a maze silage (ZM vs ZMMO). Ash contents range from 51.8 g kg ^-1 DM to 69.7 g kg ^-1 DM with MO with the highest value.

Fermentation profile

Differences between treatments were found for pH, however, all the values are among the rank of 3.7 and 4.0 reported by Kung et al (2018) for silages with no more than 40g kg ^-1 of DM. As can be seen, ZM has a lower final pH (3.7) than VU or MO because it has lower buffering capacity.

The Spearman correlation coefficient between DM and pH was r = -0.81 at p = 0.0002.

Aerobic stability of silages

The time to spoilage (p < 0.01) and pH after spoilage ( p= 0.12) were all significantly affected by treatment in the model.

Discussion

Chemical composition of silages

Unsurprisingly ZM yielded the highest DM value, which is in the range of 195 g kg-1 to 467 g kg-1 reported for many authors (Allen et al 2003; Gerlach et al 2013; McDonald et al 1991). Nevertheless, all the values observed are among those reported for well-preserved silages. (McDonald et al 2002; Mendieta-Araica et al 2011; Pezo 1991). Treatments ZM, ZMVU and ZMMO had the highest DM contents but the lowest content of CP. This also suggest that both foliage add moisture to the mixture, which causes a slight decrease in the total DM content, similar trend was reported by Contreras-Govea et al (2009) evaluating maize silage in association with M. pruriens respect to maize silage alone.

Maize has been widely used for silage purpose, mainly due to it high DM yield and Water-soluble Carbohydrates content (Khan et al 2014), however CP concentration, monoculture crop management and high demand in chemical fertilizers could be limiting factors in tropical areas therefore mixture with legumes and forage trees has been reported as a promising alternative (Castillo-Jiménez et al 2009; Contreras-Govea et al 2013; Geren et al 2008).

In this experiment, CP increased markedly with inclusion of either Vigna or Moringa on maize, mainly due to higher nitrogen availability compared with maize silage alone (ZM). While the highest CP concentration was found at the VU the lowest was at the ZM.

Inclusion of Moringa in maize silage reduced NDF content, mainly due to the use of biomass with less than five millimeters of diameter. Even when ADF concentration in silage has often been use as predictor of digestibility, in this experiment ADF showed no clear pattern.

The role of fiber (NDF and ADF) has been studied for long time and is well known its relationship with intake, feed density, chewing activity and digestibility. The inclusion either of Vigna or Moringa reduced the fiber content in silages has been also reported by Castillo-Jiménez et al (2009) and Mendieta-Araica et al (2011), therefore a striking improvement on intake can be expected.

The NDF and ADF content of mixed maize silage with either Vigna or Moringa benefit and adequate ruminal environment and a high rate of use of the material by the animal, Holland and Kezar (1995) reported that lower content of NDF and ADF generate better use at the ruminal level, since the NDF content and consumption by the animal are inversely proportional, while the ADF content is correlated with less digestible fraction of the material causing a filling effect.

Fermentation profile

Ammonia nitrogen is produced during silage fermentation due to the proteolytic action of the microorganisms of genera Clostridium and Enterobacteria (McDonald et al 2002). In general, different authors have reported that the silage ammonia nitrogen content has a negative correlation with voluntary intake. (Buxton et al 2003, McDonald et al 1991, Thomas and Fisher 1991).

Although significant differences are found among treatments for ammonia nitrogen (N-NH₃) they are like the values reported by López-Herrera and Briceño-Arguedas (2017) for silages of Vigna and Maize mixed with molasses, however, the use of either Vigna or Moringa has no significant effect on ammonia content, nevertheless, all treatments are below 5% which is the limit reported by Thomas and Fisher (1991) for well fermented silages, also there are some reports (Sánchez-Duarte and García 2017) that suggest relation between ammonia N concentration increase and reduction in dry matter intake, milk yield and fat content in milk.

From the point of view of feed production and utilization, silage making is an efficient way to ensure minimum losses and high forage quality. Thus, MO showed the lowest Weight loss while VU, ZM and ZMMO exhibited the highest values. According to (McDonald et al 2002) Dry matter losses up to 5% are expected, mainly due to the biochemical changes occurs during fermentation, especially water-soluble carbohydrate, and proteins but primarily from carbon dioxide production. Contrary to expectations, almost all treatments displayed values above 5% except MO.

Many factors could affect those losses observed: field and pre-ensiling conditions, respiration and temperature at ensiling, fermentation patterns and storage phase (McDonald et al 2002), however, Köhler et al (2013) also reported that dry matter loss was inversely and significantly related to density and feed-out rate for corn but was only related to feed-out rate for grass, that might be the plausible explanation for the lowest values of ZM and the highest values when foliage of either Vigna or Moringa where used in ZMVU or ZMMO.

Aerobic stability of silages

Once silo is open the aerobic deterioration due to the exposure of silage to air is inevitable, Borreani et al (2018) stated that the changes during the feed-out phase are equally as important as those in the closed silo from the viewpoint of preserving nutrients and maintaining good hygienic quality of the silage. This phase is also very important due to effect of feed quality and profitability in farms. The start of the deterioration process is characterized by a rise in temperature in the silage indicating increased microbial activity as the silage spoils.

The presence of Moringa caused an increase in pH after spoilage and a significant reduction in TTS. According to Mendieta-Araica et al (2009) silage with Moringa could have a somewhat lower aerobic stability after opening the silo. On the other hand, the presence of Vigna either alone (VU) or in mixture with maize (ZMVU) improves the silage to air deterioration exhibiting a good fermentation process as has also been reported by other authors (Foster et al 2011 and Andrade et al 2017).

According with Playne and McDonald (1966) protein content in the material controls 10 to 20% of the total value of the buffer capacity, this could explain the increase in the buffering capacity in treatments ZMVU or ZMMO when Vigna or Moringa are included.

Conclusion

• The CP concentration in maize silage was substantially increased by adding Vigna or Moringa foliage.
• This study also shows that the inclusion of Vigna or Moringa foliage has a positive influence in silage quality and IVDMD, the pH values where all of them on rank considered optimal.
•  In relation with aerobic stability Vigna foliage proved to be better in terms to preserve longer the silage after silo is open.

Acknownledgment

The authors would like to thank Swedish Research Link for making this joint research project possible.

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