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Article

Nutritive and Fermentative Traits of African Stargrass (Cynodon nlemfuensis Vanderyst) Forage Preserved for Silage and Haylage

by
Tania Picado-Pérez
1,
Rocky Lemus
2,
Daniel Rivera
3 and
Luis A. Villalobos-Villalobos
4,*
1
Animal Nutrition Master’s Program, Graduate School, University of Costa Rica, San Pedro, San José 2060, Costa Rica
2
Forage Extension Specialist, Mississippi State University, Starkville, MS 39762, USA
3
Southwest Research and Extension Center, Division of Agriculture, University of Arkansas, Hope, AR 71801, USA
4
Department of Animal Science and Research Center for Animal Nutrition, Campus Rodrigo Facio, University of Costa Rica, San Pedro, San José 2060, Costa Rica
*
Author to whom correspondence should be addressed.
Fermentation 2024, 10(6), 268; https://doi.org/10.3390/fermentation10060268
Submission received: 12 February 2024 / Revised: 29 March 2024 / Accepted: 30 March 2024 / Published: 22 May 2024
(This article belongs to the Section Fermentation Process Design)
Browse Figures
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Abstract

:
Climate shifts have significantly affected livestock systems due to their environmental interdependence. Among the strategies adopted by livestock systems to fill the gaps in forage biomass, preserved forages are the most commonly used. This research assessed the nutritional profile of African Stargrass (Cynodon nlemfuensis Vanderyst) preserved as silage and haylage at different feed-out periods (45, 60, 90, and 120 days). We found greater dry matter (DM) content in haylage (29.7%), with no important variations in silage over time. Stargrass silage had crude protein (CP) levels greater (13.0%) than haylage (11.9%); the former was not affected by the duration of the preservation period. Silage had lower levels of neutral detergent fiber (NDF) and higher levels of in vitro dry matter digestibility (IVDMD). The net energy for lactation (NEL) was similar for the two types of preservations evaluated. A principal component analysis (PCA) revealed that most of the variance in the dataset (69.6%) was explained by two principal components. PC1 showed that the most relevant variables were ADF, α-NDF, dNDF30, d NDF48, and NDICP, while Ash, Ca, and insoluble CP were the most relevant variables in PC2. Unlike haylage, the nutritional value of silage remained constant (p > 0.05) up to 120 days of preservation. It is important to note that haylage should not be stored beyond 90 days, regardless of the type of preservation.

1. Introduction

Livestock production systems in Latin America face challenges related to the availability, productivity, and nutritional quality of forages [1]. In tropical conditions, Ramirez-Rivera et al. [2] suggest that precipitation patterns and temperature fluctuations contribute to creating imbalances of biomass (shortages or surpluses), which in turn affect productivity and impact the production costs per kilogram of milk and meat per hectare.
Regions with seasonality in forage production tend to have contrasting conditions where livestock will not consume the surplus biomass in pastures during the rainy season, while dry matter intake is reduced during the dry season [3]. Also, the environmental conditions in the tropics may influence the net photosynthetic rate in pastures, favoring then the presence of diseases and pests that compromise the utilization of forage biomass [4].
Because most of the forage biomass (80–85%) is produced during the rainy season in tropical conditions, optimizing its utilization may allow it to fill the shortage typically occurring in the dry season [5]. Panditharatne et al. [6] suggest that a year-round supply of pasture of high nutritive quality contributes to mitigating the seasonal effects on biomass production. Either by planting additional areas or by leveraging forage surplus, preserved forages allow producers to tackle the shortfall of dry matter (DM) during critical times [7].
Ensiling is a preservation process where green forage (20–30% DM) is fermented in anaerobic conditions by bacteria that convert water-soluble carbohydrates (WSCs) into organic acids while its nutritional value is retained for long periods of storage [8]. Haylage, on the other hand, involves a similar anaerobic fermentation that preserves forage previously wilted to reach greater dry matter content (40–60%) [9].
Although perennial C4 (warm-season) grasses grown in tropical conditions are typically lower in digestibility and nutritional value, they can produce more biomass than C3 grasses due to greater efficiency in the photosynthetic pathway [10,11]. African Stargrass (Cynodon nlemfuensis Vanderyst) is a C4 perennial grass widely used in Central and South America by livestock producers [12]. Stargrass is easy to establish, with high biomass production, good palatability, and high resistance to biotic and abiotic agents [12].
Accumulated biomass between 20 and 30 t DM.ha−1 has been reported in tropical pastures [13]. Under rotational grazing systems, Villalobos et al. [14] estimated 4642 kg DM.ha−1 in African Stargrass pastures grazed at 28 d of regrowth, while tall grasses such as Taiwan (Cenchrus purpureus) yielded 11,630 kg DM.ha−1 at 112 d of regrowth in cut-and-carry systems [15].
The high yield potential and lower cost of establishment of perennial C4 grasses compared to annual forage crops, such as corn (Zea mays) and sorghum (Sorghum bicolor) [16], make them a good fit for forage preservation as silage or haylage. Perennial warm-season grasses such as Stargrass can be harvested multiple times a year [17], allowing adjustments in grazing rotation as well as allocation of paddocks for preservation.
Forage preservation has been shown to enhance forage digestibility, partly mediated by the fermentation process of anaerobic microorganisms that degrade part of the cell wall components [18].
Fewer studies have evaluated the potential to preserve African Stargrass in Costa Rica [19,20]. Because of its high yield potential and low establishment cost compared to annual crops such as corn and sorghum, African Stargrass is a forage species that can be harvested and preserved several times a year under tropical conditions. The objective of this study was to evaluate the nutritive and fermentative traits of African Stargrass preserved as silage and haylage at different preservation periods. We hypothesized that the traits evaluated would be affected by the preservation periods.

2. Materials and Methods

2.1. Study Sites

This experiment was conducted from September 2021 to January 2022 at the Dairy Cattle Experimental Station Alfredo Volio Mata (EEAVM) of the University of Costa Rica (9°55′10″ north latitude and 83°57′20″ west longitude), located in Ochomogo, Cartago, Costa Rica [21]. The station is located at 1542 m above sea level, with an average annual rainfall of 1465.9 mm from May through November, relative humidity of 84%, and average temperature of 19.3 °C. The soil is volcanic (Andosol), classified as typic distrandepts, with good drainage and medium fertility; the ecosystem is considered as Lower Montane Humid Forest [22].

2.2. Forage Management and Treatments Evaluated

A paddock of 3000 m2 planted with African Stargrass was used to prepare bags of silage and haylage. A soil sample was analyzed in the Center for Agronomic Research (CIA) of the University of Costa Rica to assess nutrient status. The pH (6.3) and exchangeable aluminum (0.12 = cmol(+) L−1) were above and below the critical levels, respectively. The macro- (Ca = 7.90, Mg = 4.10, K = 1.34 cmol(+) L−1) and micronutrients (P = 74, Zn = 73, Cu = 15, Fe = 370, and Mn = mg L−1) were above the minimum concentrations for potential fertility in the soil. The paddock was harvested at the beginning of the rainy season (late June) to remove dead material accumulated from the dry season, and the fodder harvested was used to feed dairy heifers.
The paddock was then fertilized at a rate of 200 kg N ha−1 year−1 (144 kg of urea [46% N].harvest−1) and harvested at 50 d of regrowth in late August 2021 with a FiMAKS model Double Chop 1550 forage harvester. The treatments consisted of silage or haylage preserved at four preservation periods (45, 60, 90, and 120 d) as factors, with 6 replicates per combination (n = 48 experimental units). The forage was filled and compacted in 50 kg plastic silage bags using a Silo Pack J-402 machine, with silage treatments prepared at harvest. The forage used for haylage was wilted for 48 h in a greenhouse with ventilation and flipped twice a day using pitchforks, to target a moisture content between 40 and 60% at the beginning of the preservation process.
A farm-made inoculant that has been evaluated in previous experiments [23,24,25] was prepared a week prior to harvest. The silage and haylage bags weighed approximately 18–25 kg. Sugarcane molasses (74% DM) and the farm-made inoculant (3.1 × 106 CFU Lactobacillus spp.) were applied at rates of 30 mL kg−1 and 1 mL kg−1, respectively. Temperature was assessed using 24 epoxy-coated tip sensors Omega (mod TC-PVC-K-24-180) connected to three different 8-Channel Omega Handheld thermocouple thermometers (mod OM-HL-EH-TC) that stored temperature data. Temperature was measured using thermocouples programmed for 30 min intervals, with which we could collect 2880 and 5760 data points per sensor, in all bags at 60 and 120 d (24 bags), respectively. From all the 60 and 120 d bags, we had roughly 34,560 and 69,120 data points, respectively, during the preserving period. By having this robust database, we had a better perspective of the other two treatments (45 and 90 d). The bags were airtight sealed using plastic straps to maintain anaerobic conditions throughout the preservation process. During the experiment, the bags were stored inside a greenhouse facility to protect them from weather.

2.3. Forage Sampling and Analysis

Forage samples were collected at harvest (green fodder) and two days after harvest (wilted fodder) for the silage and haylage treatments, respectively. Forage samples were analyzed with near-infrared spectroscopy (NIRS) machine using the equation of African Stargrass developed at the Forage Laboratory of the Research Center for Animal Nutrition (CINA) of the University of Costa Rica. The nutritive value before preservation allowed us to set a baseline to evaluate the changes in both treatments at different periods. Only the replications of each preservation period were opened to assess their state prior to sampling for laboratory analyses. The top 5 cm layer of each bag was discarded, and two representative samples were collected for nutritive (1.5 kg) and fermentative (1.0 kg) analyses. The latter were analyzed in the Forage Laboratory of the Research Center for Animal Nutrition of the University of Costa Rica. The remaining fodder in the bags was included in the ration of the dairy cows at the UCR Research Station.
The samples for nutritive analyses for the silage and haylage treatments were dried at 60 °C in a forced-air oven (Heratherm, Thermo Scientific, Waltham, MA, USA) for 48 h and then ground to pass a 1 mm screen in a Wiley mill (model N0. 2, Arthur H. Thomas Co., Philadelphia, PA, USA) for further analyses at Mississippi State University, Starkville, United States, using a Foss 2500 near-infrared spectroscopy machine (NIRS) (Foss North America, Eden Prairie, MN, USA) and the NIRS Forage and Feed Testing Consortium equation (Berea, KY, USA). NIRS spectrum comprised and estimated the variables of dry matter (DM), crude protein (CP), neutral detergent fiber (αNDF), acid detergent fiber (ADF), acid detergent lignin (ADL), ether extract (EE), ashes (Ash), starch (St), magnesium (Mg), phosphorus (P), calcium (Ca), digestibility of NDF at 30 h (dFDN30), digestibility of NDF at 48 h (dNDF48), in vitro digestibility of the DM at 30 h (IVDMD30), in vitro digestibility of the DM at 48 h (IVDMD48), ether-soluble carbohydrates (ESC), water-soluble carbohydrates (WSC), neutral detergent insoluble crude protein (NDICP), acid detergent insoluble crude protein (ADICP), and insoluble CP (ICP).
NIR is widely used for routine forage analysis in commercial laboratories [26,27], allowing to prediction of the nutrient composition of forages based on a regression against a reference method from established data from wet chemistry samples. The data in this study have been validated, and regression and validation confidence intervals were used to ensure the predictability of the samples with low bias and standard error of prediction.
The pH was evaluated on the same day of the sample collection in the Laboratory of Anatomy and Physiology of the Animal Science Department, at the University of Costa. Fifty grams of the sample was deposited in a 500 mL beaker and distilled water was added; a portable HANNA® HI 98,127 pH meter was then introduced into the beaker and waited to stabilize to get the pH reading. Buffer capacity [28] and ammonia nitrogen [29] were determined in the Laboratory of the Research Center for Animal Nutrition of the University of Costa Rica.

2.4. Experimental Design and Statistical Analysis

The experimental design was a randomized complete block design with a 2 × 4 factorial, with two treatments (silage and haylage) and four preservation periods (45, 60, 90, and 120 d) and six replications (n = 48). The data for nutritive and fermentative traits were analyzed using a generalized linear model (GLM) procedure in R-Studio [30], with mean separations by treatment or factor using the least significant difference (LSD) post hoc test. The databases for temperature were also analyzed by the GLM procedure in R-Studio. Temperature was measured as a continuous variable over time, while the preservation periods were treated as categorical variables using specific time intervals (45, 60, 90, and 120 d). Significance for all variables was set at p ≤ 0.05, and tendencies were set at p > 0.05 and p ≤ 0.10. Multivariate statistics methods were applied by using a principal components analysis (PCA) with the nutritive data in R-Studio. Principal component analysis was based on a correlation matrix, and scree plots were used to determine the number of principal components retained as well as to indicate the contributions of the nutritional variables in each component.

3. Results

3.1. Nutritive Value of African Stargrass Silage and Haylage

Before preservation, the nutritional value of African Stargrass was evaluated for both processes to set a baseline for the forage. The two-day wilting period increased the dry matter content of African Stargrass, as well as the NDF and ADF contents (Table 1). The increase in fiber reduced the DNDF and IVDMD in the wilted forage. Although wilting reduced the CP and EE concentrations in the forage, it in turn increased the net energy of lactation (NEL).
The dry matter before preservation in both silage and haylage was lower than each treatment across all four different preservation periods (Figure 1A). The preservation periods had an impact on the dry matter content in both treatments (p < 0.05). The dry matter concentration increased significantly after 45 d in silage. For haylage, there was a gradual increase in dry matter concentration up until 90 d, after which it decreased by 120 d. The type of preservation exhibited significant differences (p < 0.05) with higher concentrations of dry matter in haylage along the periods (Figure 1A).
The CP concentrations for both silage and haylage were lower for the green fodder (Table 1). The type of preservation significantly (p < 0.05) affected the CP concentrations (Figure 1B), having silage overall greater (p < 0.05) concentration of CP compared to haylage. Similar concentrations of CP were found for haylage (p > 0.05) at all periods evaluated (Figure 1B). Although the CP concentration of African Stargrass silage varied at different preservation periods, the lowest concentration found at 60 d was yet similar to that at 30 d.
The NDF concentration in African Stargrass preserved was lesser in silage than in haylage at all periods (Figure 1C). Regardless of the method of preservation, the NDF concentration was also lower for both silage and haylage after preservation. The NDF concentration in haylage decreased (p < 0.05) at 60 and 90 d when compared to 45 and 120 d, whereas similar concentrations were found for silage with differences lesser than one percentage point (pp) among the preservation periods evaluated.
The in vitro dry matter digestibility (IVDMD) was significantly greater (p < 0.05) in silage compared to haylage (Figure 1D). The digestibility increased in silage after 60 d, while it decreased in haylage after having similar and greater values up until 60 d.
The concentration of ADF was greater and was highest at 120 and 90 d for haylage and silage, respectively (Table 2).
The acid lignin concentration (ADL) showed no significant differences (p > 0.05) between preservation periods for silage, while a greater (p < 0.05) concentration of ADL was found at 120 d for haylage (Table 2). Before preservation, ADL had concentrations as high as 2.6% and 2.3% pp lesser for haylage and silage, respectively. The EE was not affected by the preservation periods in both treatments (p > 0.05). The starch concentration was similar during the preservation periods for haylage (p > 0.05) and it varied for silage. At 60 d of preservation, African Stargrass silage had the highest concentration of starch and the lowest was at 90 and 120 d periods with no significant differences (p > 0.05) between these periods.
Fiber digestibility (DNDF) was greater at 45 d for both silage and haylage (Table 2) with a significant (p < 0.05) decrease in the successive periods. The DNDF before preservation was greater for both preservation techniques. The energy (NEL) was not affected (p > 0.05) by the preservation periods for haylage and silage.

3.2. Fermentative Characteristics of African Stargrass Silage and Haylage

The pH in silage was significantly different (p < 0.05) than in haylage (Figure 2A), with the lowest values in the former. The pH was similar throughout the preservation periods on silage (p > 0.05), while a significant increase in pH was found for haylage at 120 d of storage (Figure 2A).
The concentration of water-soluble carbohydrates (WSCs) varied both between treatments and during the preservation periods (Figure 2B). In haylage, the WSC increased during the conservation period, with the greatest concentrations found at 90 and 120 d while compared to 45 d, but similar to 60 d. Similarly, the lowest concentration of WSC in silage was at 45 d, and the greatest concentrations were at 60 and 90 d, but the latter showed no difference from the 120 d period.
The concentration of ammonia nitrogen (as a percentage of total N) increased during the preservation period in both treatments with significant differences (p < 0.05) between silage and haylage (Figure 2C). African Stargrass haylage had greater concentrations of ammonia nitrogen than silage. The ammonia nitrogen concentrations remained similar (p > 0.05) at 45 and 60 d of preservation for haylage and increased at 90 d (p < 0.05), reaching its highest concentration at 120 d. Silage had similar (p > 0.05) ammonia nitrogen concentrations up until 90 d, and like haylage, the greatest concentration of ammonia nitrogen occurred at 120 d in silage (Figure 2C).
The buffer capacity (BC) showed differences between treatments (p = 0.0012, Figure 2D) as well as a result of the conservation period for silage (p = 0.0013) and haylage (p = 0.0419). In both treatments, the BC was lowest at 45 d and steadily increased until 120 d of conservation.

3.3. Temperature

The temperature was different between treatments during the first 60 d (9-week period) of conservation (p < 0.05, Figure 3). Stargrass haylage had on average greater temperatures than silage. The temperature reached its greatest values in the first and third weeks in both treatments. Except for weeks fourth and seventh, when there was a temperature drop in both treatments, the values recorded were relatively constant.
The bags where temperature was recorded for 120 d (18-week period) showed a similar pattern to those at 9 weeks (Figure 4). Greater temperatures were common during the first and third weeks of conservation in both treatments. Similarly, the highest average temperature was in haylage when compared to silage but with similar fluctuations in temperature for both treatments (Figure 4).

3.4. Principal Component Analysis (PCA)

The results of the PCA showed that most of the variance in the dataset (69.6%) was explained by two principal components. The variables that represent the highest contribution to the components were those close to the circumference, and the ones near the diameter of each component were less relevant in the variance. The principal component 1 (PC1) explained 57.0% of the variance (Figure 5), grouping on the right the variables related to the insoluble fraction of CP, ash, and fiber components and it grouped to the left the variables related to cell content and digestibility. The PC2 explained 12.6% of the variance.
For the first component, all variables contributed to the variance and were essential in the analysis; however, the variables slightly more relevant were ADF, α NDF, dNDF30, dNDF48, and NDICP, all related to cell structure. All these variables were positively associated with an insoluble fraction of the CP in the cell wall. The IVTDMD 48, IVTDMD 30, and ESC represented the highest contribution negatively related to variables of Mg, Ca, WSC, CP, P, and fat. The variables of insoluble CP and ash were the variables with the lowest contribution. The principal component 2 (PC2) was highly influenced by the variables of Ash, Ca, and insoluble CP, and the variables with the lowest contribution were CP, P, and ADF.
According to the centroid of each group (Figure 6) from the PCA, the African Stargrass haylage was the treatment located in the most fibrous quadrant with greater dry matter concentration, while silage was the treatment in the quadrant where the most digestible components are located (cell content and digestibility).

4. Discussion

4.1. Nutritive Value of African Stargrass Silage and Haylage

The type of fermentation in silage is determined by the dry matter concentration of the plant [31]. In our study, the African Stargrass silage did not exceed 24.5% of dry matter. Granados-Marin et al. [19], under similar conditions (3% molasses and 60 d preservation), obtained 26.2% DM. Preserving forages with high moisture promotes butyric fermentation and the release of ammonia, which has been shown to reduce the intake of silage by animals [32]. Optimizing moisture levels in forage prior to ensiling is crucial to mitigate the risk of undesirable fermentation outcomes and subsequent reductions in silage quality. The differences in dry matter content between studies highlight the significance of this practice.
Because of differences before the start of the preservation process, the DM concentration of haylage was expected to be greater than silage. The greatest DM concentration found in our study for haylage was 29.7% at 90 d of conservation, after wilting the fodder for 2 d in a greenhouse facility and using pitchforks to flip it two times per day. Borreani et al. [33] found DM values of 52.2% in haylage, using a mix of temperate grasses while McCormick et al. [34] reported DM concentrations of 50.2% in Paspalum notatum L. haylage. Although wilting has proven benefits such as increasing the concentration of fermentable substrate and preventing the development of unwanted bacteria by reducing moisture content [35], in our study, the wilting was not sufficient to increase the DM content of both silage and haylage of African Stargrass.
The decrease in DM concentration found in haylage at 120 d may reduce the shelf-life and affect the nutritive value and fermentation profile. In tropical conditions, Nath et al. [36] suggested that the conservation period for fodder as haylage tends to be shorter, with forages losing stability after 60 d. In our study, the DM concentration in haylage increased at 90 d, which may be a benefit of the additives applied. However, the decrease in DM at 120 d to levels lower than those observed at 45 d may be an indicator of DM losses after losing stability [36].
The CP concentration of haylage was lesser than silage at all periods evaluated, indicating the loss of nitrogen during the wilting and fermentation processes. The decrease in CP concentration in haylage, as noted by Rooke and Hatfield [37], is an inevitable consequence of protein degradation (proteolysis) occurring during the wilting and preserving processes, leading to alteration in the nitrogenous constituents of the conserved forage. The decrease in crude protein (CP) concentration in haylage compared to silage emphasizes the significance of comprehending the protein degradation dynamics during the conservation process. Costa et al. [38] found that the protein fraction decreased p < 0.05) after 14 d of haylage production, after which it remained stable until 56 d. The length of the wilting period and the prevailing climatic conditions play a significant role in the extent of the proteolysis. The protein fraction remained stable in the two methods evaluated in this study, which might indicate that proteolysis was not extensive and African Stargrass both as silage and haylage can maintain CP levels up to 120 d.
Silages can be stable starting at 1 month and up to 3 months after sealing, which occurs due to the lactic acid reaching its greater concentration while acetic acid remains stable [39]. Vendramini et al. [40] and Pineda et al. [20] reported values of 10.9% and 9.98% CP, respectively, in African Stargrass silage. Both values are lesser than those obtained in our study for both silage and haylage at all conservation periods. Considering the factors that influence CP content in silage and haylage (e.g., harvest timing, preserving techniques, and storage conditions), it is necessary to optimize nutrient composition and feed quality.
The NDF concentrations reported by Pineda et al. [20] and Granados-Marin et al. [19] in African Stargrass silage were 71.00% and 59.94%, respectively. Both results are greater than those obtained in this study. Villalobos and Arce [24], on the other hand, found greater NDF concentrations in Kikuyu silage (Cenchrus clandestinus ex Chiov) than those found in our study, but these authors also reported lower NDF concentrations in perennial Ryegrass (Lolium perenne) and Italian Ryegrass (Lolium multiflorum), which are temperate grasses (C3). The NDF in African Stargrass silage remained unaffected over time, whereas for haylage, there were significant decreases at 60- and 90 d periods, concurring with a significant decrease in fiber digestibility. In a previous study, Dehghani et al. [41] found that changes in the digestible and indigestible fractions of NDF affected the proportion of NDF within the total dry matter. The variation in NDF concentrations among different studies underscores the impact of factors such as forage species, preserving techniques, and preserving periods. While African Stargrass silage had relatively stable NDF levels, haylage exhibited significant decreases over time, which could affect its fiber digestibility. Also, the changes experienced by the fibrous fraction of haylage can be attributed to changes in DM and the loss in stability mentioned above.
The digestibility in both silage and haylage in our study was greater than the values reported by Granados-Marin et al. [19] in African Stargrass silage (51.65–64.88%) with 60 d of preservation. The IVDMD decreased especially after 90 d of conservation in haylage, which coincides with the changes in DM and loss in stability of the process. The decrease in IVDMD following 90 d of preservation in haylage indicates potential constraints in extended storage, potentially resulting from alterations in dry matter content and stability. The net energy for lactation (NEL) contents determined by Granados-Marin et al. [19] in African Stargrass silage (1.18 to 1.26 Mcal-kg−1 DM) were similar to those obtained in our study for silage but greater than those for haylage. Although the NEL was not affected by the type of conservation and the period in our study, the silage not only had greater values than haylage but those were maintained up until 120 d. The slightly superior NEL content of silage suggests that it may offer a more energy-dense feed option for livestock, potentially contributing to improved animal performance and production efficiency.

4.2. Fermentative Characteristics of African Stargrass Silage and Haylage

Our study showed pH values ranging from 4.1 to 5.5, being greater in haylage than silage as it also occurred in other studies, where the increase in DM increased the pH as well [42]. The pH at 90 d of preservation with 25% DM showed a value of 4.8 [43] and 5.2 at 56 d of preservation and 70.4% DM [38], both results with Tifton 85 bermudagrass (Cynodon sp.), a forage of the same genus of African Stargrass. Other studies evaluating African Stargrass as silage obtained pH values of 7.4, 4.7, and 5.5 [19,20,40]. Although the preservation period increased in pH at 120 d in haylage, the value was still in the normal range reported in the literature. The pH increase with higher dry matter content is in line with previous research and indicates a transition towards less acidic fermentation conditions. Despite the pH increase during the preservation period, the values remained within acceptable ranges reported in the literature, indicating the maintenance of suitable fermentation conditions for preserved forage.
The presence of soluble carbohydrates plays a crucial role in ensuring the production of high-quality silage. According to McDonald et al. [31], the silage potential of a plant is contingent upon its water-soluble carbohydrate (WSC) content, ideally exceeding 8% in dry matter (DM). Nevertheless, it is widely acknowledged that tropical grasses inherently possess lower levels of soluble carbohydrates; Kagan et al. [44] reported 6.3% WSC in Bermudagrass and 4.3% in Tifton 85 Bermudagrass before preservation [36]. Values of 1.4, 1.25, and 1.63% WSC were obtained in silage of different tropical grasses [45,46,47], similar to WSC in haylage. Understanding the dynamics of WSC content during conservation is crucial for developing strategies to enhance fermentation efficiency and improve silage nutritive value. The increase in WSC content after 60 d in silage can be explained by the hydrolysis of starch, being consistent with the decrease in starch in silage at the same period. Previous studies showed an increase of 3–4% WSC by adding starch to the silage [48,49]. The increase in WSC after conservation indicates the potential for starch hydrolysis to contribute to carbohydrate availability, suggesting avenues for enhancing silage quality through supplementation strategies.
The type of forage determines the fermentation end products. For grass silage (25–30% DM), the typically suggested concentration of NH3-N of total N is 8–12% [50]. Our results were lower in both treatments. Values of 1.7, 2.7, and 2.0% in African Star grass and Bermudagrass in previous studies [19,42,51] were lower than ours. The variability between the two fermentation processes is demonstrated by the ammonia nitrogen concentrations. This variability is influenced by forage type, dry matter content, and preserving conditions. Ammonia nitrogen concentration in silage in our study indicated lower proteolysis intensity during the fermentation process, due to the lower performance of clostridial bacteria [31]. In haylage, compaction was difficult due to the low DM content and may have led to aerobic conditions within the silo that promoted the growth of undesirable bacteria and, consequently, increased ammonia nitrogen.
The preserving period, in both treatments, increased the buffering capacity to values significantly greater than those recommended for corn (20–25 mEq NaOH 100 g−1 DM) and legume silages (50–55 mEq NaOH 100 g−1) [50]. Granados-Marín et al. [19] reported a buffering capacity of 78.0 mEq NaOH 100 g−1 in African Stargrass silage at 60 d, which is less than the values found in our study during this period. While the buffering capacity in our study exceeded typical recommendations for corn and legume silages, it underscores the inherent resilience of African Stargrass preserved to pH fluctuations. However, it has been reported that buffering capacity may increase markedly in silage, which can occur rapidly and may double within three days after preservation due to the formation of lactates and acetates [52]. Although the buffering capacity in our study was greater than expected, it also indicates that the preserved African Stargrass remained stable and less susceptible to abrupt changes in pH throughout the periods evaluated.

4.3. Temperature

In our study, the temperature of haylage was consistently greater than that of silage throughout the entire conservation process. Our data showed lesser pH in the silage bags that reached greater temperatures (up to 40 °C) at some hours during the day, with respect to those of intermediate values (28 °C) as reported in a previous study [53]. Although it has been mentioned that the average temperature of silage should not exceed more than 5 to 8 °C above the ambient temperature [50], both silage and haylage bags that recorded greater temperatures in our study did not show any signs of spoilage at the feed-out phase. Dry silages tend to be more susceptible to yeast and mold growth during the conservation process due to a slower fermentation that yields lesser antifungal acids [50]. During the first week (Figure 4A), haylage bags reached temperatures greater than 30 °C, though no evidence of spoilage was found when compared to silage bags. Even for silages, Ashbell et al. [54] exposed wheat and maize silages to ambient temperatures of 40 °C and found greater aerobical stability than those stored at 20 or 30 °C. Preserving forages in the tropics may take longer than 45 d due to the unique climate conditions, such as high temperature and humidity, and forage characteristics, such as high moisture content and low soluble carbohydrates, which make forage preservation more challenging.
The forage preserved in combination with the ambient temperature may influence the type of fermentation. Temperate forages as well as maize and sorghum create a lactate-dominated fermentation, while tropical grasses are prone to yield more acetic acid [6,55]. Greater temperatures have also been shown to favor acetic acid-dominated environments within preserved forages [53]. The presence of acetic acid in warmer environments indicates a shift towards more aerobic conditions during fermentation, thus affecting the microbial communities and metabolic pathways involved in forage preservation. Understanding these interactions is crucial for optimizing silage production techniques and enhancing nutrient retention in preserved forages across diverse climatic regions.

4.4. Principal Component Analysis (PCA)

The nutritive value and fermentative characteristics of haylage differed from silage. This distinction is due to differences in the fermentation process and the changes experienced by the fodder before being preserved (wilting). PC 1 was strongly associated with cellular content and dry matter digestibility while PC 2 structural variables were slightly more relevant. Costa et al. [40] indicate that a high DM content in haylage limits bacterial fermentation capacity, does not produce sufficient acid, and becomes resistant to pH decline. This characteristic should also be considered alongside other factors as the fermentation parameters for haylage should differ from those recommended for silage.
Overall, haylage had greater fiber and dry matter contents with respect to silage, the latter having greater cell content and digestibility. According to the centroid of each group (Figure 6), haylage was the treatment located in the most fibrous quadrant with greater DM content, while silage treatment was located in the most digestible quadrant with greater cell content.

5. Conclusions

Most of the variables evaluated were not affected by the conservation periods. However, there were significant differences in ammonia nitrogen and buffer capacity, which increased with longer conservation periods. Temperature measurements have shown that the conservation process differs between haylage and silage due to differences in the composition of the fodder as well as the wilting process that both experienced before the start of the fermentation. The variation of the data according to the PCA was mostly explained by the fiber components and the in vitro digestibility of the dry matter. The main contributions in haylage were related to fiber and insoluble fraction of CP contents, whereas in vitro digestibility of dry matter and cell content were the main contributors to silage.
The fermentative characteristics of African Stargrass silage suggest a more thorough fermentation process, while haylage’s overall quality decreases after 90 d of storage, indicating a loss of stability in the process. Therefore, African Stargrass preserved as silage may be stored for a longer period than haylage.

Author Contributions

Conceptualization, R.L. and L.A.V.-V.; methodology, T.P.-P., R.L. and L.A.V.-V.; software, T.P.-P. and R.L.; validation, T.P.-P., R.L. and L.A.V.-V.; formal analysis, T.P.-P., R.L. and L.A.V.-V.; investigation, T.P.-P., R.L. and L.A.V.-V.; resources, R.L. and L.A.V.-V.; data curation, T.P.-P. and R.L.; writing—original draft preparation, T.P.-P. and L.A.V.-V.; writing—review and editing, T.P.-P., R.L., D.R. and L.A.V.-V.; visualization, T.P.-P., supervision, R.L. and L.A.V.-V.; project administration, R.L. and L.A.V.-V.; funding acquisition, R.L. and L.A.V.-V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the U.S. Department of Agriculture, Foreign Agriculture Service (FAS) and the project “Sustainable Intensification and Technology Transfer of Preserved Forage Systems to Improve Dairy Production in Central America” under award number FX20SR-10961R002. And the APC was funded by the Vicerrectoría de Investigación of the Universidad de Costa Rica.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data used in this study are available upon request to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Nutritive value of African Stargrass haylage and silage at four preservation periods: (A) dry matter, (B) crude protein, (C) neutral detergent fiber, and (D) in vitro dry matter digestibility. The dots inside the boxes represent the mean of each treatment, the bold horizontal bars represent the median, and the boxes correspond to the lower and upper quartiles. Treatment means are indicated with the SEM in parentheses. Different letters (capital for haylage and lowercase for silage) are indicative of statistical differences among the means of each treatment.
Figure 1. Nutritive value of African Stargrass haylage and silage at four preservation periods: (A) dry matter, (B) crude protein, (C) neutral detergent fiber, and (D) in vitro dry matter digestibility. The dots inside the boxes represent the mean of each treatment, the bold horizontal bars represent the median, and the boxes correspond to the lower and upper quartiles. Treatment means are indicated with the SEM in parentheses. Different letters (capital for haylage and lowercase for silage) are indicative of statistical differences among the means of each treatment.
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Figure 2. Fermentative characteristics and water-soluble carbohydrates of African Stargrass haylage and silage in four preserving periods: (A) pH, (B) water-soluble carbohydrates, (C) ammonia nitrogen, and (D) buffer capacity. The dots inside the boxes represent the mean; the horizontal bars are the medians of each treatment, and the boxes correspond to the lower and upper quartiles. Treatment means are indicated with the SEM in parentheses. Different letters (capital for haylage and lowercase for silage) are indicative of statistical differences among the means of each treatment.
Figure 2. Fermentative characteristics and water-soluble carbohydrates of African Stargrass haylage and silage in four preserving periods: (A) pH, (B) water-soluble carbohydrates, (C) ammonia nitrogen, and (D) buffer capacity. The dots inside the boxes represent the mean; the horizontal bars are the medians of each treatment, and the boxes correspond to the lower and upper quartiles. Treatment means are indicated with the SEM in parentheses. Different letters (capital for haylage and lowercase for silage) are indicative of statistical differences among the means of each treatment.
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Figure 3. Temperature of haylage and silage of African Stargrass in 9 weeks of preservation: (A) haylage and (B) silage. Treatment means are indicated with the SEM in parentheses. Different letters are indicative of statistical differences among the treatment means.
Figure 3. Temperature of haylage and silage of African Stargrass in 9 weeks of preservation: (A) haylage and (B) silage. Treatment means are indicated with the SEM in parentheses. Different letters are indicative of statistical differences among the treatment means.
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Figure 4. Temperature of haylage and silage African Stargrass in weeks of preserving period: (A) haylage and (B) silage. Treatment means are indicated with the SEM in parentheses. Different letters are indicative of statistical differences among the treatment means.
Figure 4. Temperature of haylage and silage African Stargrass in weeks of preserving period: (A) haylage and (B) silage. Treatment means are indicated with the SEM in parentheses. Different letters are indicative of statistical differences among the treatment means.
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Figure 5. Principal component analysis of the nutritive traits for African Stargrass preserved as silage and haylage. The intensity of the color indicates the contribution of the traits at each component.
Figure 5. Principal component analysis of the nutritive traits for African Stargrass preserved as silage and haylage. The intensity of the color indicates the contribution of the traits at each component.
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Figure 6. Principal component analysis grouping treatments in different quadrants of preserved forage (silage and haylage) of African Stargrass.
Figure 6. Principal component analysis grouping treatments in different quadrants of preserved forage (silage and haylage) of African Stargrass.
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Table 1. Nutritional value of African Stargrass before preserving as silage and haylage.
Table 1. Nutritional value of African Stargrass before preserving as silage and haylage.
ParameterFresh (Silage)Wilted 48 h (Haylage)
Dry matter 120.827.3
Nutritive values 2
CP 13.912.7
EE3.52.9
αNDF 68.671.3
ADF36.438.5
ADL2.83.8
DNDF56.553.2
IVDMD 70.266.6
NEL1.11.3
1 Dry matter determined by drying in forced air for 48 h at 60 °C. 2 All nutritive values determined with NIRS and reported on a DM basis: CP, crude protein; EE, ether extract; NDF, neutral detergent fiber with amylase; ADF, acid detergent fiber; ADL, acid detergent lignin; DNDF, digestibility of neutral detergent fiber; IVDMD, in vitro dry matter digestibility; NEL, net energy of lactation.
Table 2. Nutritive value of African Stargrass silage and haylage at four preservation periods.
Table 2. Nutritive value of African Stargrass silage and haylage at four preservation periods.
Preservation Period (d)ADFADLEEStarchDNDFNEL
Haylage
4543.46 B5.87 B2.26 0.32 38.57 A1.18
6042.52 D5.94 B2.19 0.35 37.02 B1.17
9042.86 C6.11 B2.18 0.22 36.60 C1.17
12043.86 A6.47 A2.13 0.16 37.07 B1.12
Silage
4537.76 ab4.92 2.83 0.86 b34.94 a1.29
6037.41 c5.18 2.65 1.26 a33.91 c1.25
9037.94 a4.95 2.78 0.16 c34.59 b1.28
12037.66 bc5.02 2.76 0.15 c34.12 c1.28
DM, dry matter; CP, crude protein; EE, ether extract; NDF, neutral detergent fiber; ADF, acid detergent fiber; ADL, acid detergent lignin; DNDF, digestibility of neutral detergent fiber; IVDMD, in vitro dry matter digestibility. abc Preservation methods with the same lowercase letter in a column of silage are not significantly different from each other at α = 0.05. ABCD Preservation methods with the same capital letter in a column of haylage are not significantly different from each other at α = 0.05.
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Picado-Pérez, T.; Lemus, R.; Rivera, D.; Villalobos-Villalobos, L.A. Nutritive and Fermentative Traits of African Stargrass (Cynodon nlemfuensis Vanderyst) Forage Preserved for Silage and Haylage. Fermentation 2024, 10, 268. https://doi.org/10.3390/fermentation10060268

AMA Style

Picado-Pérez T, Lemus R, Rivera D, Villalobos-Villalobos LA. Nutritive and Fermentative Traits of African Stargrass (Cynodon nlemfuensis Vanderyst) Forage Preserved for Silage and Haylage. Fermentation. 2024; 10(6):268. https://doi.org/10.3390/fermentation10060268

Chicago/Turabian Style

Picado-Pérez, Tania, Rocky Lemus, Daniel Rivera, and Luis A. Villalobos-Villalobos. 2024. "Nutritive and Fermentative Traits of African Stargrass (Cynodon nlemfuensis Vanderyst) Forage Preserved for Silage and Haylage" Fermentation 10, no. 6: 268. https://doi.org/10.3390/fermentation10060268

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