Influence of Adding Dehydrated Medicago sativa on the Nutritional Parameters Related to Hedychium gardnerianum Silage Quality

Abstract

This study investigated using Hedychium gardnerianum, an invasive plant, combined with dehydrated alfalfa (Medicago sativa) with varying percentages of alfalfa: control (0% alfalfa), T1 (10%), T2 (20%), T3 (30%), and T4 (40%), to enhance nutritional parameters in silage for ruminants in the Azores. Samples were vacuum-sealed and stored for 45 days at room temperature to promote anaerobic fermentation. Chemical analysis showed that alfalfa addition increased dry matter (DM) from 12.33% to 48.04% and crude protein from 11.34% DM to 24.63% DM. Insoluble fiber levels decreased, enhancing digestibility. In vitro fermentation indicated higher gas production in 40% alfalfa silage, suggesting faster fermentation. In conclusion, incorporating dehydrated alfalfa into Hedychium gardnerianum silage particularly enhances nutritional quality and digestibility. This approach offers a practical solution for ruminant feed in the Azores, particularly during feed scarcity periods.

1. Introduction

In the face of climate change affecting forage availability, sustainable alternatives are needed. The Azores archipelago, made up of nine islands of volcanic origin, offers a unique setting for study due to its geographical, climatic, and agricultural characteristics [1]. The ecological diversity of the islands, together with the oceanic climatic conditions and the predominance of andosol soils [2], creates a particular environment for agriculture, an activity of great economic importance in the region [3].

In this context, livestock production has evolved and become the main economic activity in the archipelago, with most farms using rotational grazing systems or semi-permanent stabling [4]. However, pasture production faces considerable challenges due to climate change, which affects the availability and quality of feed for ruminants [5]. The scarcity of pasture during the summer and winter months forces farmers to resort to alternatives such as silage to maintain adequate animal nutrition [6].

Silage, a method of preserving green forage plants through anaerobic fermentation, has proven to be an effective solution for minimizing food shortages and meeting the nutritional needs of animals during critical periods [7]. Recently, the use of invasive plants such as Hedychium gardnerianum, known locally as “Roca-de-velha” [8], has been explored as a viable solution, despite its nutritional limitations, which include a low crude protein content, high levels of neutral detergent fiber (NDF) and acid detergent fiber (ADF), and low digestibility [9]. Hedychium gardnerianum, belonging to the Zingiberaceae family, is a perennial herbaceous plant that can reach up to 2 m in height, with a large number of alternate, ovate–elliptic leaves measuring between 20 and 60 cm in length. The inflorescences are composed of yellow–orange flowers, and during flowering, the mature seed heads exhibit an intense red color [8]. This family of plants includes about 47 genera and 1400 species, distributed across tropical and subtropical regions. The chemical composition of Hedychium gardnerianum includes various compounds such as alkaloids, flavonoids, terpenoids, and phenols, which can influence the digestibility and nutritional value of the plant when used as forage. Alkaloids are known for their pharmacological properties, including antibacterial and analgesic effects, while flavonoids act as antioxidants, reducing oxidative stress in cells. Terpenoids contribute to the aromatic properties of the plant and have anti-inflammatory benefits, and phenolic compounds are essential due to their antioxidant capacities and role in the plant’s defense against herbivores [2].

Hedychium gardnerianum thrives in humid habitats and fertile soils, being found in various types of habitats, including tropical forests, natural forests, planted forests, high-altitude forests, agricultural areas, coastal zones, scrublands, and even urban areas. It is native to India and Nepal, where it grows at 1250 m on the lower slopes of the Himalayas. The production of this plant does not require active cultivation due to its invasive nature, but it can be harvested for various uses, including silage production. From an animal nutrition perspective, Hedychium gardnerianum silage has a low dry matter content of crude protein and low dry matter digestibility, as demonstrated by previous studies. Although it has low nutritional quality on its own, its ability to grow in marginal areas where other crops may not thrive makes it a valuable resource during forage scarcity. However, its invasive nature can threaten local biodiversity as it competes with native species for resources. When combined with high-nutritional-value plants such as Medicago sativa (alfalfa), it can improve the diet of ruminants [8].

Alfalfa is a highly valued forage crop due to its high protein content and ability to improve soil fertility through biological nitrogen fixation [10]. Introduced to the Azores at the beginning of the 20th century, alfalfa has gained prominence, especially on Terceira Island, where it is grown in coastal and low-lying areas. Alfalfa, particularly when dehydrated, significantly enhances the nutritional profile of silage due to its high crude protein content and favorable fiber composition, making it an excellent supplement to improve the overall quality of mixed silages. Specifically, alfalfa’s high protein content and balanced fiber composition (low levels of neutral detergent fiber (NDF) and acid detergent fiber (ADF)) contribute to improving the crude protein content, digestibility, and overall nutritional value of Hedychium gardnerianum when used in mixed silage.

Hedychium gardnerianum silage is characterized by low protein and a low dry matter content, and the inclusion of dehydrated alfalfa aims to enrich its nutritional value. This study sought to determine whether the inclusion of dehydrated alfalfa in Hedychium gardnerianum silage improved its overall suitability as animal feed. The primary objective was to evaluate whether this combination produced a more nutritious silage suitable for animal feed by examining changes in its chemical composition. By addressing these aspects, this study aimed to provide a comprehensive assessment of the potential benefits of using dehydrated alfalfa to enhance the quality of Hedychium gardnerianum silage.

2. Materials and Methods

2.1. Sample Collection and Preparation

Samples of Medicago sativa (alfalfa), produced by local farmers from Angra do Heroísmo, Terceira Island, Azores, were collected, along with samples of Hedychium gardnerianum, an invasive non-conventional plant species, from which leaves and stems were harvested locally in the same region. Both plants were manually harvested. For this study, five samples of Hedychium gardnerianum were collected, and ten samples of Medicago sativa (alfalfa).

2.2. Ensiling Procedure

The alfalfa was artificially dried in a laboratory oven with air circulation to achieve a dry matter content of 88.20%, as indicated in Table 1, after which it was chopped into pieces of 2–3 cm in length. Samples of Hedychium gardnerianum were allowed to wilt for 24 h and subsequently chopped into pieces of 2–3 cm in length as well. Subsequently, the alfalfa samples were mixed with the Hedychium gardnerianum samples, varying the proportions of dried alfalfa according to the following treatments:

TC: Control, only Hedychium gardnerianum.

T1: Hedychium gardnerianum + 10% dried alfalfa.

T2: Hedychium gardnerianum + 20% dried alfalfa.

T3: Hedychium gardnerianum + 30% dried alfalfa.

T4: Hedychium gardnerianum + 40% dried alfalfa.

Table 1. Chemical compositions (mean ± SD) of Hedychium gardnerianum, alfalfa, and dehydrated alfalfa before ensiling.

Parameter	Hedychium gardnerianum	Alfalfa	Dehydrated Alfalfa
DM (%)	12.07 ± 2.24	10.10 ± 1.57	88.20 ± 2.51
CP (%DM)	7.27 ± 2.20	19.54 ± 2.12	16.51 ± 1.16
NDF (%DM)	69.94 ± 3.84	38.95 ± 2.93	45.40 ± 2.51
ADF (%DM)	43.35 ± 3.20	26.73 ± 1.57	30.56 ± 1.36
ADL (%DM)	10.15 ± 1.20	5.83 ± 0.83	6.14 ± 0.13
EE (%DM)	2.18 ± 0.12	2.41 ± 0.07	2.18 ± 0.81
Ash (%DM)	9.28 ± 1.32	10.89 ± 2.92	11.20 ± 1.87
IVDMD (%)	30.60 ± 2.23	69.60 ± 3.86	60.12 ± 2.90
IVOMD (%)	27.97 ± 1.87	57.39 ± 2.54	55.63 ± 2.15

DM: dry matter, CP: crude protein, NDF: neutral detergent fiber, ADF: acid detergent fiber, ADL: acid detergent lignin, EE: ether extract, IVDMD: in vitro dry matter digestibility, IVOMD: in vitro organic matter digestibility.

Table 1. Chemical compositions (mean ± SD) of Hedychium gardnerianum, alfalfa, and dehydrated alfalfa before ensiling.

Parameter	Hedychium gardnerianum	Alfalfa	Dehydrated Alfalfa
DM (%)	12.07 ± 2.24	10.10 ± 1.57	88.20 ± 2.51
CP (%DM)	7.27 ± 2.20	19.54 ± 2.12	16.51 ± 1.16
NDF (%DM)	69.94 ± 3.84	38.95 ± 2.93	45.40 ± 2.51
ADF (%DM)	43.35 ± 3.20	26.73 ± 1.57	30.56 ± 1.36
ADL (%DM)	10.15 ± 1.20	5.83 ± 0.83	6.14 ± 0.13
EE (%DM)	2.18 ± 0.12	2.41 ± 0.07	2.18 ± 0.81
Ash (%DM)	9.28 ± 1.32	10.89 ± 2.92	11.20 ± 1.87
IVDMD (%)	30.60 ± 2.23	69.60 ± 3.86	60.12 ± 2.90
IVOMD (%)	27.97 ± 1.87	57.39 ± 2.54	55.63 ± 2.15

DM: dry matter, CP: crude protein, NDF: neutral detergent fiber, ADF: acid detergent fiber, ADL: acid detergent lignin, EE: ether extract, IVDMD: in vitro dry matter digestibility, IVOMD: in vitro organic matter digestibility.

After mixing, 6 kg of samples was weighed and packed into transparent mini silos (30 cm × 50 cm) made of a polyethylene-polyamide composite with a thickness of 0.14 mm. The samples were then compacted and sealed under vacuum using a packaging machine (ECO VAC, Italy) to promote anaerobic fermentation. The sealed silos did not allow for gases or effluents to escape and were stored in a dark place at room temperature for a period of 45 days. Each treatment was conducted in triplicate to ensure result reliability

At the end of this period, the samples were removed from the silos for chemical analysis, allowing for the evaluation of the quality and composition of the produced silages.

To ensure standardized conditions for subsequent analytical assessments of the remaining chemical and biological parameters, all silage samples underwent a meticulous drying process in a forced-air oven set at 65 °C until achieving a constant weight. Post-drying, the samples were meticulously ground through a 1 mm screen using a Retsch mill, facilitating precise and uniform preparation for comprehensive analyses.

2.3. Chemical Analyses

2.3.1. Determination of the Chemical Parameters

For the analytical characterization, we employed the Weende scheme [11] to ascertain the DM (dry matter, method 930.15), ash (crude ash, method 942.05), EE (ethereal extract, method 920.39), and CP (crude protein, method 954.01) using the Kjeldhahl method. NDF (neutral detergent fiber), ADF (acid detergent fiber), and ADL (acid detergent lignin) were gauged following the procedures outlined by [12].

2.3.2. Determination of Biological Parameters

In vitro DMD (dry matter digestibility) and OMD (organic matter digestibility) were assessed following the procedure outlined by [13], with modifications introduced by [14]. Gas production was quantified in accordance with the methodology proposed by [15].

The gas production constants utilized were derived from the model developed by [16] and were fitted to the gas production kinetics curve described by [17].

$$y=a+b(1-e^{\left(-ct\right)})$$

(1)

where $y$ represents the gas production at time $t$; a is the gas production of the immediately soluble fraction (mL 200 mg⁻¹ DM); $b$ is the gas production of the insoluble fraction (ml 200 mg⁻¹ DM); $c$ is the gas production rate constant for the insoluble fraction (h⁻¹); and $t$ is the incubation time, in hours (1).

Rumen fluid for each digestibility and gas production experiment was procured from cows the local slaughterhouse, following the procedures detailed by [18].

2.4. Energy Estimates

Gross energy (GE) (2), digestible energy (DE) (3), metabolizable energy (ME) (4), and net energy for lactation (NEL) (5) were estimated utilizing the following equations [19,20,21]:

$$GE\left({\displaystyle \frac{\mathrm{M}\mathrm{J}}{\mathrm{k}\mathrm{g}\mathrm{D}\mathrm{M}}}\right)=18.45-(0.088\times NDF)$$

(2)

$$DE\left({\displaystyle \frac{\mathrm{M}\mathrm{J}}{\mathrm{k}\mathrm{g}\mathrm{D}\mathrm{M}}}\right)=GE\times {\displaystyle \frac{DMD}{100}}$$

(3)

$$ME\left({\displaystyle \frac{\mathrm{M}\mathrm{J}}{\mathrm{k}\mathrm{g}\mathrm{D}\mathrm{M}}}\right)=DE\times 0.82$$

(4)

$$NEL\left({\displaystyle \frac{\mathrm{M}\mathrm{J}}{\mathrm{k}\mathrm{g}\mathrm{D}\mathrm{M}}}\right)=0.101GP+0.051CP+0.11EE$$

(5)

NDF is the neutral detergent fiber (%DM), DMD is the dry matter digestibility (%), CP is the crude protein (%DM), and EE is the ether extract (%DM).

2.5. Flieg’s Point Calculation

As a silage quality index, Flieg points were calculated with the following Equation (6):

$$Flieg\text{’}s point=220+\left(2\times DM-15\right)-40\times pH$$

(6)

DM is the dry matter (%).

According to this index [22], the quality of silage is classified as follows: 20 denotes very bad quality, 21–40 signifies bad quality, 41–60 represents average quality, 61–80 indicates good quality, and 81–100 signifies very good quality.

2.6. Statistical Analyses

All the data were statistically analyzed using SPSS Statistics Software v.27 (IBM SPSS, Inc., Chicago, IL, USA).

Initially, the data obtained were submitted to the Shapiro–Wilk normality test. This test indicated that the data followed a normal distribution, which allowed the use of one-way analysis of variance (one-way ANOVA).

The one-way analysis of variance was then used to identify whether there were significant differences between the means of the different silage treatments. The criterion for statistical significance was set at a p-value of less than 0.05. Therefore, when the p-value resulting from the ANOVA was less than 0.05, it was concluded that there were significant differences between the means of the treatments. This rigorous statistical procedure ensures the reliability of the results obtained, allowing a precise analysis of the effects of the different treatments on the silages.

3. Results

The chemical compositions of Hedychium gardnerianum (HG), alfalfa, and dehydrated alfalfa before ensiling are presented in Table 1. HG has low dry matter (12.7%), low crude protein (7.27% DM), and a low dry matter digestibility (30.60%) content, indicating its limitation as a primary forage source. In contrast, alfalfa and dehydrated alfalfa have much higher CP and digestibility levels, which are essential for a balanced and efficient ruminant diet. The high concentration of fiber (NDF ADF and ADL) in HG reflects its lower digestibility, while alfalfa and dehydrated alfalfa show lower levels, suggesting greater nutritional efficiency.

The results obtained from the chemical analysis of the different silage samples, presented in

Table 2. Effects of the addition of different levels of alfalfa on the chemical compositions of silages after 45 days of ensiling.

Parameter	Silage Composition					SEM	p-Value
	TC	T1	T2	T3	T4
DM (%)	12.33 a	27.87 b	35.51 c	43.03 d	50.04 e	0.49	<0.001
pH	5.00 a	5.72 b	5.88 c	6.05 d	6.06 d	0.05	<0.001
N-NH3/N (%)	8.49 a	10.12 b	11.01 c	12.57 d	13.03 e	0.17	<0.001
CP (%DM)	11.34 a	15.29 b	18.77 c	20.67 d	24.63 e	0.20	<0.001
NDF (%DM)	77.64 a	66.17 b	58.74 c	57.42 c	48.44 d	1.80	<0.001
ADF (%DM)	37.93 a	36.79 a	33.65 bc	32.54 b	31.82 c	0.60	<0.001
ADL (%DM)	10.88 a	8.56 b	7.62 b	7.75 ab	8.74 b	0.61	0.004
EE (%DM)	2.16 a	4.03 b	3.52 b	3.47 a	3.67 b	0.41	0.010
Ash (%DM)	9.78 a	10.94 b	11.21 c	11.60 d	11.63 d	0.07	<0.001
IVDMD (%)	20.83 a	31.34 b	41.12 c	45.04 cd	50.10 d	1.76	<0.001
IVOMD (%)	14.85 a	25.84 b	35.39 c	40.21 c	45.97 d	1.68	<0.001

DM: dry matter, CP: crude protein, NDF: neutral detergent fiber, ADF: acid detergent fiber, ADL: acid detergent lignin, EE: ether extract, IVDMD: in vitro dry matter digestibility, IVOMD: in vitro organic matter digestibility, TC: control (only Hedychium gardnerianum silage), T1: Hedychium gardnerianum silage + 10% dehydrated alfalfa, T2: Hedychium gardnerianum silage + 20% dehydrated alfalfa, T3: Hedychium gardnerianum silage + 30% dehydrated alfalfa, T4: Hedychium gardnerianum silage + 40% dehydrated alfalfa, SEM: standard error of the mean. Different letters next to the respective value indicate significant differences in the nutritive parameters among sampling dates. p < 0.05: significant differences were found.

, show significant changes in composition depending on the percentages of dehydrated alfalfa added. A gradual increase in the percentage of DM was observed as the amount of dehydrated alfalfa increased, indicating that alfalfa contributes significantly to the DM content of the silages. The TC treatment (only Hedychium gardnerianum) had the lowest DM value (12.33%), while the treatment with 40% alfalfa (T4) had the highest value (50.04%).

The pH of the silages also varied, with the samples with the highest percentages of dehydrated alfalfa having a higher pH. The pH varied from 5.00 in the control to 6.07 in treatment T4. An increase in ammoniacal nitrogen values was observed with the increasing proportion of alfalfa in the samples.

When dehydrated alfalfa was added, there was a significant increase in the CP content of the silages, reflecting the high protein concentration of alfalfa. The TC treatment had 11.34% DM of CP, while the treatment with 40% alfalfa reached 24.63% DM.

The addition of alfalfa resulted in a decrease in NDF, ADF, and ADL.

The digestibility of dry matter (DMD) and organic matter (OMD) increased with the increase in alfalfa in the silage, reflecting better fermentation and nutritional quality.

The estimates of gross energy (GE), digestible energy (DE), metabolizable energy (ME), and net energy for lactation (NEL) for various silage compositions (TC, T1, T2, T3, and T4) are presented in

Table 3. Estimates of gross energy (GE), digestible energy (DE), metabolizable energy (ME), and estimated net lactation energy (NEL).

Parameter	Silage Composition					SEM	p-Value
	TC	T1	T2	T3	T4
GE (MJ/kgDM)	11.62 a	12.63 a	13.28 b	13.40 b	14.19 b	0.09	<0.05
DE (MJ/kgDM)	2.42 a	3.96 b	5.46 c	6.03 c	7.10 d	0.23	<0.05
ME (MJ/kgDM)	1.98 a	3.24 b	4.48 c	4.95 c	5.83 d	0.20	<0.05
NEL (MJ/kgDM)	2.40 a	2.93 a	3.19 ab	3.29 b	3.61 b	0.15	<0.05

SEM: standard error of the mean. Different letters next to the respective value indicate significant differences in the nutritive parameters among sampling dates. p < 0.05: significant differences were found.

. The data show that gross energy (GE) significantly increases with the percentage of dehydrated alfalfa in the silage, indicating that alfalfa enhances the overall energy density of the silage. Digestible energy (DE) also significantly increases (p < 0.05) with the inclusion of dehydrated alfalfa, reflecting improved digestibility. Similarly, metabolizable energy (ME) rises significantly with the addition of dehydrated alfalfa, demonstrating that alfalfa not only boosts digestibility but also enhances energy availability for animal metabolism.

Furthermore, net energy for lactation (NEL) consistently increases with the inclusion of dehydrated alfalfa, though the differences are less pronounced compared to DE and ME. Nonetheless, the increase in NEL remains statistically significant (p < 0.05)

According to the Flieg index (Figure 1) for silage quality, T4 has a good preservation quality, T2 and T3 have satisfactory preservation, while TC and T1 represent badly preserved silage.

Table 4. Cumulative fitted values of gas production (mL/200 mgDM).

Incubation Time (h)	TC	T1	T2	T3	T4	SEM	p-Value
4	1.72	2.30	2.50	2.03	1.45	0.74	0.768
8	4.96	5.03	6.59	6.14	5.92	0.60	0.241
12	7.97	7.58	10.24	9.78	6.28	0.71	0.080
24	15.71 a	16.94 ab	18.31 bc	18.40 bc	19.35 c	1.00	0.003
48	26.75	24.22	29.56	28.57	27.22	1.41	0.079
72	33.73	30.89	34.89	33.51	32.25	1.49	0.243
96	38.16	35.38	37.58	35.90	34.82	1.54	0.254

SEM: standard error of the mean. Different letters next to the respective value indicate significant differences. p < 0.05: significant differences were found.

shows the cumulative gas production data for the different treatments over the incubation time (4 h, 8 h, 12 h, 24 h, 48 h, 72 h, and 96 h).

In the first few hours, in the control (TC), gas production was 1.72 mL/0.2 gDM after 4 h and increased to 7.97 mL/0.2 gDM after 12 h, indicating rapid initial fermentation. Meanwhile, the T4 treatment showed the lowest initial gas production (1.45 mL/0.2 g MS after 4 h), increasing to 6.28 mL/0.2 gDM after 12 h, suggesting a slower initial fermentation.

Gas production was highest in the control (TC), followed by the sample with 10% alfalfa (T1). This production decreased progressively with the addition of alfalfa, with the lowest production being observed in the treatment with 40% alfalfa (Figure 2).

Table 5. In vitro gas production kinetic parameters of the different silages.

Kinetics Parameters	TC	T1	T2	T3	T4	SEM	p-Value
a (mL/0.2 gDM)	−1.79 ab	−0.05 a	−2.09 b	−2.60 b	−2.06 b	0.60	0.015
b (mL/0.2 gDM)	47.82 a	45.45 ab	42.42 bc	40.77 bc	39.59 c	1.12	0.453
c (mL/h)	0.0191 a	0.0167 a	0.0286 b	0.0301 b	0.0281 b	0.02	<0.001
tlag(h)	2.00	1.07	1.73	2.17	1.93	0.61	0.370

SEM: standard error of the mean. Different letters next to the respective value indicate significant differences. p < 0.05: significant differences were found.

shows the parameters of the in vitro fermentation kinetics of the different treatments. The a constant of the reaction kinetics varied between −0.05 mL/0.2 g MS for treatment T1 and −2.09 mL/0.2 g MS for treatment T2, while the b constant of the reaction kinetics varied between 39.59 mL/0.2 g MS for treatment T4 and 47.82 mL/0.2 g MS for the TC treatment. The c constant varied between 0.0013 mL/h and 0.0286 mL/h.

The lag t, which indicates the time elapsed before gas production began, varied between 2 h for the TC treatment and 1.07 h for the T1 treatment.

4. Discussion

Climate change significantly impacts agriculture by altering temperatures, rainfall, and soil moisture, leading to droughts and reduced production [23,24].

The search for sustainable strategies, including non-conventional forages, is crucial to address forage shortages and enhance economic and environmental sustainability. Research is focused on understanding their impact on reproduction, nutritional composition, and greenhouse gas mitigation [25,26,27,28].

Understanding forage characteristics is crucial for animal feed production [29], making crop conservation essential for a year-round feed supply [30]. In the Azores, the use of non-traditional feed resources like Hedychium gardnerianum is promising due to limited growing seasons.

From an animal nutrition point of view (Table 1), Hedychium gardnerianum has low dry matter contents (12.07%), in line with previous findings by [31], consolidating its reputation as a potential source of water, especially during periods of drought. It also has low levels of crude protein (7.27% DM) and dry matter digestibility (30.60%), similar to the values found by [32].

The same study showed that Hedychium gardnerianum silage without additives leads to increased dry matter (DM) losses and the accumulation of fiber components, resulting in a decrease in in vitro dry matter digestibility. This is a significant problem for its use in animal feed because increased DM losses reduce the amount of usable feed available for livestock. Additionally, the accumulation of fiber components such as neutral detergent fiber (NDF) and acid detergent fiber (ADF) lowers the overall digestibility of the silage. Lower digestibility means that animals are less able to extract necessary nutrients from the feed, leading to decreased feed efficiency and potential nutritional deficiencies. Therefore, improving the fermentation process and reducing the fiber content through the inclusion of additives like dehydrated alfalfa is essential for enhancing the quality and suitability of Hedychium gardnerianum silage for animal feed [33].

Table 2, which highlights the chemical composition, serves as a starting point for observing marked differences between silages with varying levels of alfalfa added. The DM content increased with higher proportions of alfalfa, and only the silages with moderate levels of dehydrated alfalfa achieved the recommended DM content of between 30% and 35% [30], for optimal fermentation in the silo.

The pH of the silages varied significantly, with the samples containing the highest percentages of dehydrated alfalfa exhibiting higher pH values. This variation in pH can be attributed to differences in dry matter content and the buffering capacity of alfalfa. Higher dry matter levels can influence the fermentation process and pH stability.

Moreover, the increase in ammoniacal nitrogen concentration observed in the silages with higher dehydrated alfalfa contents can be explained by the higher protein content in alfalfa. During ensiling, proteolysis occurs, leading to the breakdown of proteins into amino acids and subsequently to ammonia. The higher the initial protein content, the greater the potential for ammonia production. This increased ammonia production can raise the pH levels, particularly in silages with higher proportions of alfalfa. This mechanism is consistent with findings from previous studies, which have reported a direct correlation between the protein content of the forage and the ammoniacal nitrogen levels in the resulting silage [34]. The presence of dehydrated alfalfa thus leads to higher ammoniacal nitrogen levels, aligning with the findings of other studies [35].

The increase in crude protein (CP) content is the main advantage of mixed silage production [36,37]. The addition of dehydrated alfalfa significantly enhanced the crude protein content in the silages, with the T4 treatment showing the highest improvement compared to the TC treatment.

This increase is beneficial, as a higher crude protein (CP) content is essential for adequate ruminant nutrition and to support efficient rumen fermentation [38]. Additionally, according to [39], crude protein values higher than 15% of dry matter (DM) are necessary for optimal growth and lactation in dairy cattle.

The contents of neutral detergent insoluble fiber (NDF) and acid detergent insoluble fiber (ADF) decrease with the addition of dehydrated alfalfa. NDF drops significantly from the TC treatment to the silage with the highest level of alfalfa (T4), while ADF also shows a noticeable reduction between the same treatments. These results suggest that the inclusion of alfalfa improves silage digestibility, since lower NDF and ADF values are associated with better digestibility [30].

The acid detergent lignin (ADL) content decreases from the TC treatment to the T4 treatment, showing a reduction in lignin levels with the addition of dehydrated alfalfa. The reduction in lignin content is positive, as lignin is indigestible, and its presence can limit fiber digestibility.

The dry matter digestibility (DMD) content emerges as a key indicator, directly influencing the digestive efficiency in ruminants [40]. Hedychium gardnerianum presented DMD values below the 30% (Table 1) threshold, indicating potential inadequacy to meet the animals’ maintenance needs. This finding corroborates previous studies suggesting that the digestibility of shrubs and trees is underestimated due to the presence of secondary metabolites such as tannins or saponins, which can negatively impact in vitro digestibility values [41]. With the addition of alfalfa, the in vitro dry matter digestibility (DMS) and in vitro organic matter digestibility (DMO) significantly increased, indicating an improvement in the nutritional quality of silages (Table 2). These improvements can be attributed to the reduction in the fractions of cell wall fiber, although the values achieved are still lower than those previously obtained by [33].

The results of the in vitro gas production kinetics, summarized in Table 4 and Figure 2, indicate significant differences in the fermentation patterns of the silages. According to [42], the amount of gas produced during in vitro fermentation reflects the extent of fermentation and the digestibility of a forage, which is directly proportional to the rate of substrate degradation. Our findings support this, as the fermentation kinetics described in Table 5 show varied degradation rates and extents.

During the initial incubation period, the fermentation of soluble and rapidly fermentable fractions of the substrate, such as soluble carbohydrates, occurs, alongside the synthesis of microbial protein [43]. This is followed by the fermentation of insoluble but potentially degradable components, such as the NDF fraction [44]. The model described by [16] was used to characterize these kinetics.

The constant a of the reaction kinetics consistently showed negative values, indicating a lag phase where cell wall degradation had not yet begun, as suggested by [45]. This behavior aligns with the expected initial phase of no degradation, which precedes the rapid breakdown of components.

Significant differences in the b and c parameters among the treatments suggest varied fermentation dynamics. Notably, the silage with 40% dehydrated alfalfa (T4) demonstrated faster and more extensive fermentation, consistent with [46]. The lag time (Lag T), indicating the time before gas production began, varied between 1.07 and 2 h, corresponding with the negative a value observed. This variation in lag time further underscores the differences in fermentation onset among the treatments.

These results highlight the impact of adding dehydrated alfalfa on the fermentation characteristics of silage, indicating that higher proportions of alfalfa enhance both the rate and extent of fermentation, leading to improved digestibility and nutrient availability.

When exploring the energy estimates (Table 3), the importance of including dehydrated alfalfa in silage is highlighted. With significant increases in GE, DE, ME, and NEL, it is clear that the addition of dehydrated alfalfa not only increases the total amount of energy available, as in other studies [47], but also the quality and efficiency of utilization of this energy by the animals. These improvements are crucial for optimizing animal production, especially in periods of conventional forage scarcity, ensuring that animals receive an energy-rich diet to maintain their health and productivity.

5. Conclusions

In summary, the inclusion of dehydrated alfalfa in Hedychium gardnerianum silage significantly improves its nutritional quality and digestibility. This practice increases the dry matter and crude protein content while reducing the concentration of indigestible fibers. These findings support the objective of producing a more nutritious and suitable silage for animal feed.

To further validate these results, field trials under various environmental and soil conditions, along with long-term studies, are recommended. Additionally, an economic analysis is essential to assess the cost-effectiveness of producing and using this modified silage, ensuring its feasibility for local producers.

These measures will help strengthen the sustainability and efficiency of livestock production in the Azores, offering a viable solution during periods of forage scarcity and benefiting both farmers and the local environment.