In vitro digestibility evaluation of Axonopus Scoparius under Ecuadorian conditions: baseline results

Avaliação da digestibilidade in vitro de Axonopus scoparius em condições equatorianas: resultados de base

Abstract

Axonopus scoparius, a native forage grass species of the Ecuadorian Amazon, holds significant potential as a sustainable feed resource for ruminant production systems, yet its nutritional characteristics remain insufficiently studied. This research aimed to evaluate the in vitro dry matter digestibility (IVDMD) of A. scoparius collected from six ecological zones with altitudes ranging from 280 to 945 meters above sea level. The study assessed digestibility across three incubation periods (24, 48, and 72 hours) using the established Tilley and Terry two-stage technique to simulate ruminal fermentation and post-ruminal digestion. Samples were systematically collected to represent diverse altitudinal and ecological conditions, providing insights into how environmental factors influence forage quality. Statistical analyses included analysis of variance (ANOVA), Tukey’s multiple comparison tests, and regression modeling to examine the effects of incubation time and altitude on digestibility outcomes. Results demonstrated a significant increase (P < 0.01) in IVDMD with longer incubation, with mean values rising from 22.46% at 24 hours, to 30.74% at 48 hours, and reaching 37.81% after 72 hours of fermentation. Altitude was a significant factor affecting digestibility (P = 0.004); notably, samples from mid-altitude zones (600–750 m.a.s.l.) showed the highest digestibility levels, up to 42.4%, whereas lower altitude zones exhibited values as low as 26.8%. Regression analysis revealed a positive correlation between incubation time and digestibility at 72 hours (r = 0.5289, R² = 0.2797, p = 0.0079), highlighting the importance of extended fermentation periods to capture the full nutritional potential of this grass species. While A. scoparius exhibits moderate digestibility compared to improved tropical forages, its natural adaptability to poor soils, resilience to overgrazing, and minimal input requirements position it as a valuable forage option for extensive tropical livestock systems. These preliminary findings advocate for the integration of A. scoparius into forage diversification strategies and suggest further research focusing on agronomic practices, supplementation, and genetic improvement to enhance its nutritive value.

Keywords:
in vitro digestibility; Ecuadorian forages; feed evaluation; sustainable livestock

Resumo

Axonopus scoparius, uma gramínea forrageira nativa da Amazônia equatoriana, possui potencial significativo como fonte alimentar sustentável para sistemas de produção de ruminantes, porém suas características nutricionais permanecem pouco estudadas. Esta pesquisa teve como objetivo avaliar a digestibilidade in vitro da matéria seca (DIVMS) de A. scoparius coletada em seis zonas ecológicas com altitudes variando de 280 a 945 metros acima do nível do mar. O estudo avaliou a digestibilidade em três períodos de incubação (24, 48 e 72 horas), utilizando a técnica de dois estágios de Tilley e Terry para simular a fermentação ruminal e a digestão pós-ruminal. Amostras foram coletadas sistematicamente para representar diversas condições altitudinais e ecológicas, permitindo compreender como os fatores ambientais influenciam a qualidade da forragem. As análises estatísticas incluíram análise de variância (ANOVA), testes de comparação múltipla de Tukey e modelagem de regressão para examinar os efeitos do tempo de incubação e da altitude nos resultados de digestibilidade. Os resultados demonstraram um aumento significativo (P < 0,01) na DIVMS com incubação mais longa, com valores médios aumentando de 22,46% em 24 horas, para 30,74% em 48 horas, atingindo 37,81% após 72 horas de fermentação. A altitude foi um fator significativo que afetou a digestibilidade (P = 0,004); notavelmente, amostras de zonas de média altitude (600–750 m.a.s.l.) apresentaram os maiores níveis de digestibilidade, até 42,4%, enquanto zonas de menor altitude exibiram valores tão baixos quanto 26,8%. A análise de regressão revelou uma correlação positiva entre o tempo de incubação e a digestibilidade em 72 horas (r = 0,5289, R² = 0,2797, p = 0,0079), destacando a importância de períodos prolongados de fermentação para capturar todo o potencial nutricional desta espécie de gramínea. Embora A. scoparius apresente digestibilidade moderada em comparação com forrageiras tropicais melhoradas, sua adaptabilidade natural a solos pobres, resiliência ao sobrepastoreio e requisitos mínimos de insumos a posicionam como uma opção valiosa de forragem para sistemas pecuários extensivos em regiões tropicais. Esses resultados preliminares defendem a integração de A. scoparius em estratégias de diversificação de forragem e sugerem pesquisas adicionais com foco em práticas agronômicas, suplementação e melhoramento genético para aumentar seu valor nutritivo.

Palavras-chave:
digestibilidade in vitro; forragens equatorianas; avaliação de ração; pecuária sustentável

1. Introduction

In rural areas, livestock production faces numerous challenges, particularly concerning the quality and availability of feed (Guamán-Rivera et al., 2024). These challenges are compounded by competition between human food production and animal grazing needs (Bernués et al., 2011; Moorby and Fraser, 2021; Haldar et al., 2022). The optimization of forage resources for ruminant nutrition is a critical component of sustainable livestock production, especially in tropical regions where climate variability and soil constraints often limit productivity (Robinson et al., 2006; Schlageter-Tello et al., 2020; Morais et al., 2023). Among the available tropical grasses, Axonopus scoparius has emerged as a promising species due to its adaptability to low-fertility soils, tolerance to acidic pH (Lima et al., 2001b; Lajús et al., 2014), and resistance to grazing (Lima et al., 2001a). Axonopus scoparius, also known as carpet grass, belongs to the Poaceae family and is often undervalued compared to more commercialized species like Brachiaria or Panicum (Lima et al., 2001b). Nonetheless, its resilience and low input requirements make it a valuable candidate for low-cost grazing systems (Low, 2015; Silva-olaya et al., 2022; González Marcillo et al., 2021), especially for smallholder farmers (Bienabe et al., 2004; Berre et al., 2017). For this reason, digestibility is one of the most important parameters to evaluate the nutritional quality of forages (Nikkhah, 2013; Capstaff and Miller, 2018), as it directly affects voluntary intake, nutrient absorption, and animal performance (Euclides et al., 2016; Guamán-Rivera et al., 2023a). In vitro digestibility assays provide an efficient, cost-effective alternative to in vivo trials (Preston et al., 2017), allowing researchers to estimate the fermentation capacity and nutrient availability of a given forage sample using ruminal fluid and controlled incubation techniques (ANKOM, 1920). The in vitro gas production technique and the Tilley and Terry method are among the most commonly used methodologies for estimating digestibility in laboratory conditions (Tilley and Terry, 1963). In addition, the chemical composition and digestibility of forages can be highly influenced by multiple factors (Larbi et al., 1998; Fox, 1996; Apori et al., 2000), including plant maturity, harvest season, fertilization, and climate (AOAC, 2000). Therefore, its potential contribution to animal productivity cannot be fully harnessed without a clear understanding of its nutritional properties, including crude protein content, fiber fractions (NDF, ADF), and digestibility coefficients (Reid et al., 1988; Van Soest et al., 1991). Under Ecuadorian tropical conditions, variations in rainfall and temperature can significantly impact the structural development and fibre content of grasses, thus affecting their utilization by ruminants (Guamán Rivera et al., 2023b; Guamán-Rivera et al., 2024). Therefore, it is crucial to conduct local evaluations of forage species to generate reliable nutritional data that can guide ration formulation and pasture management strategies (Guamán-Rivera et al., 2025a; Guamán-Rivera et al., 2025b). In this context, In Vitro digestibility evaluation becomes an essential tool not only for quantifying nutritional quality but also for supporting decisions on supplementation and pasture rotation (Wilson and Hattersley, 1989; Rosales, 1996). Furthermore, integrating digestibility data with chemical composition allows the classification of forages based on their fermentative potential, which is key to achieving balanced diets in tropical systems that often rely on fibrous and variable-quality pastures (Da-Silveira et al., 2010; Da Silva et al., 2021). In fact, despite its widespread use in native pastures across various regions of Ecuador, there is limited scientific data available regarding its nutritional value and digestibility potential, particularly under localized environmental and management conditions (Lima et al., 2001b). Given the scarcity of published information on Axonopus scoparius under Ecuadorian ecological conditions, the present study aims to bridge this knowledge gap by evaluating its in vitro digestibility. By doing so, it seeks to provide baseline data that will be useful for animal nutritionists, researchers, and livestock producers in designing sustainable feeding strategies. The results may also contribute to promoting the rational use of native and adapted grasses that are often overlooked in favor of introduced species, despite their ecological and economic advantages. Therefore, this study focuses on determining the in vitro dry matter digestibility of Axonopus scoparius collected under typical management and climate conditions of the Ecuadorian tropics. Through laboratory assays and standardized procedures, the research seeks to provide a scientific basis for the incorporation of this species into more productive and resilient grazing systems.

2. Materials and Methods

2.1. Study design

Under a completely randomised block model (BDCA), plots of 3 × 3 m² were established with Axonopus scoparius on 8 altitudinal levels in the province of Morona Santiago (Gualaquiza, San Juan Bosco, Limón Indanza, Santiago de Méndez, Tiwintza, Logroño, Morona and the parish of 9 de octubre). The province of Morona Santiago is at an altitude of 1150 meters above sea level, it has a rainfall of 274 mm, relative humidity of 80.95%, while the average temperature is 25°C. The Axonopus scoparius was established in 2016 at 3kg/ha

seeding rate. Besides this, the experimental area was fertilized with 195 kg N/ha applied at seeding. In April 2024, grazing began using a frequency 35-day rest period and 20 cm of cutting height.

2.2. Forage collection

Samples of approximately 0.5 kg of Axonopus scoparius of each localization was collected. The sample was dried in the forced air circulation oven at 60 ºC for 72 h in order to determine dry matter (DM kg ha-¹), while one-second sample was milled and homogenized through a cyclone mill (Retsch SM2000, Retsch, Haan, GE) with a 2 mm mesh (Ørskov et al., 1980) and placed in ANKOM sleeves 57 for In Vitro digestibility.

2.3. In vitro digestibility

Measurement of on in vitro DM digestibility (IVDMD) was performed according to Tilley and Terry (1963). For this, the rumen fluid as inoculant source was collected from two fistulated dairy bulls (450 ± 7 kg BW), following standard laboratory procedures. For fermentability measurement, the samples (three replications) were incubated with rumen liquor, added with buffer and aerated with CO₂ to produce an anaerobic condition. The amount of rumen liquor and buffer used were vary according to the methods. The fermenters were sealed with rubber stopper and put into 39oC water shaker bath for 4 h. Supernatant were collected from the fermentability test tubes after adding 2 drops of HCl to stop the fermentation process and centrifuged at 3500 rpm for 15 minutes (Despal et al., 2022).

The DMD digestibility measurement consisted of two steps, so, each step lasted for 24 h. The first step followed a similar procedure as the fermentability test. In the second stage, sample residues were incubated with 2% HCl-pepsin enzyme (50 ml). After the enzymatic digestion, the feed residues were filtered using the predetermined weight of no 41 Whatman paper. The filter paper was dried at 105°C oven to determine DM residue and then incinerated at 600°C for 4 h to determine ash residue. In vitro DMD was calculated by subtracting DM residues from samples.

2.4. Statistical analysis

This experiment used a block randomized design. The data were analysed using ANOVA and continued with the Tukey test with SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Prior to analysis, Normality was visually tested in all continuous variables using the UNIVARIATE procedure of SAS and tested for homogeneity of variance by the Kolmogórov-Smirnov procedure. Therefore, differences were considered significant when P < 0.05.

3. Results and Discussion

Table 1 shows the in vitro digestibility values ​​of Axonopus scoparius grass as a function of the altitudinal range. Aumont et al. (1995) stated that the in vivo dry matter (DM) digestibility of tropical forages is the main criterion for the determination of nutritive values. In general, regardless of location, Axonopus scoparius grass showed digestibility values ​​below 30% under in vitro conditions. But the Tiwintza canton stands out with a digestibility of 26 ± 0.2% which differs numerically compared to the percentages of the other localities (P = 0.03 to 0.04; Table 1). A reference study by Costa et al. (2015) observed a large variation in in vitro digestibility values ​​according to the season, although much higher than ours (54.53 vs. 30%). According to Despal et al. (2022) digestibility value can be used as an early indication of nutrients available in the feed that can be used by the animal. Similar to reported by Salazar-Cubillas and Dickhoefer (2021) in Ecuador, freshly cultivated forages are a major source of protein for domestic ruminants, particularly in the tropics and subtropics. In this sense, tropical forages generally have low protein and high fibre content, which decreases animal production efficiency (Morais et al., 2023). Therefore, higher NDF content of pastures results in a numerically lower dry matter intake for ruminants (Preston et al., 2017). In all ways, factors of variation, such as the season, level of nitrogen fertilization as well as maturation stage should be considered (Guamán-Rivera et al., 2023b).

Table 1
Digestibility of Axonopus scoparius grass depending on the location of the province of Morona Santiago.

Localization	Mean ± SD	P = value
Morona	23.54 ± 0.6ab	0.02
Logroño	22.00 ± 0.3b	0.03
Nueve de Octubre	24.36 ± 0.5ab	0.04
Gualaquiza	22.97 ± 0.4ab	0.02
San juan B	22.70 ± 0.4ab	0.02
Limon	23.36 ± 0.1ab	0.02
Tiwintza	26.18 ± 0.2a	0.001
Mendez	24.52 ± 0.2ab	0.03

• ^a-b Means with different letters in the same row differ at P < 0.001; SD, standard deviations

Figure 1 shows the percentage of digestibility at 72 hours. Indeed, the experiment was conducted over 72-hour periods to analyse the percentage of digestibility of grasses as a function of time, considering it as a study variable, due to the relationship between nutrient absorption and digestibility time. The digestibility yielded a value of 27.71% as the maximum expressed when it was subjected to a period of 72 hours, while the digestibility found at 48 hours was 24.32 and 19.08% at 24 hours (P < 0.001), so it can be said that as the time of incubation period to this process increases, the digestibility of the grass increases.

Figure 1
Digestibility values according to incubation time.

Lima et al. (2001b) reported greater values of digestibility than those observed in this study at 48 h (62.25 vs. 24.32%). We conjecture that greater neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin (LAD) contents in Axonopus scoparius could possibly explain the lowest disappearance levels (Fuentes-Quisaguano et al., 2023). In effect, Hoover (1986) reported a high correlation (r = −76; P < 0.001) between dry matter (DM) intake and (NDF) contents. Based on several scientific evidence, Tilley and Terry´s method (1963) is more relevant to be used as in a vitro method in accessing fermentability and digestibility of tropical dairy ration. Therefore, as the determination of the nutritional value of forage plants

has high importance and complexity, it is normally used in vivo and in situ methods for evaluation, which is not always possible because as it requires considerable use of cannulated animals, food stocked, hand labour, time and high costs, thus limiting their applicability (Reis et al., 2016). From a production perspective, these results indicate that Axonopus scoparius grass should be better managed since pastures with digestibility values ​​below 50% could affect good animal performance. Referential studies by Ortiz-Ortiz and Zhunio-Borja (2024) have reported crude protein (CP) values ranging from (7.68 to 10.69%). Givens et al. (2000) stated that, forages with CP content less than 7% in DM have been found to reduce DMI.

The in vitro digestibility assessment of Axonopus scoparius under different incubation periods (24, 48, and 72 hours) reveals important insights into the forage’s fermentation dynamics and potential nutritional value for ruminant diets, as shown in Table 2. At 24 hours of incubation, the correlation coefficient (r = 0.1267) and coefficient of determination (r² = 0.0161) suggest a very weak relationship between incubation time and digestibility, with only 1.6% of the variability explained by the model. The slope of the regression (b = 20.9460) is modest, and the non-significant Fisher test (P = 0.5551) indicates that the relationship is not statistically supported, implying that digestibility is not well captured at this early stage. After 48 hours, the correlation improves to r = 0.3325 and r² = 0.1106, meaning that approximately 11.1% of the variability in digestibility can now be attributed to the incubation period. Although the regression slope increases (b = 31.7404), indicating a steeper rise in digestibility, the Fisher test remains statistically no significant (P = 0.1124), though approaching a trend-level threshold. This suggests that, while digestibility is improving, the relationship is still not strong enough to confirm a reliable pattern. At 72 hours, however, the data show a marked enhancement in digestibility, as the correlation becomes strong (r = 0.5289) and the coefficient of determination rises significantly to r² = 0.2797. This means nearly 28% of the digestibility variation is explained by the model, which is further validated by the highly significant Fisher test result (P = 0.0079). The regression slope reaches its highest point (b = 40.4162), indicating a substantial increase in digestibility with prolonged incubation. Lima et al. (2001b) reported slightly higher values of b fraction of several Axonopus cultivars than obtained in Axonopus scoparius (0.36 vs. 31.0). The integration of livestock and crop production systems has gained attention for its potential to enhance sustainability and resource efficiency in agricultural practices. This study evaluated the in vitro digestibility of Axonopus scoparius, a grass species, under Ecuadorian conditions. In this sense, this outcome demonstrates that Axonopus scoparius has greater digestibility potential than reflected an earlier time points. In nutritional terms, these findings highlight the importance of considering longer incubation periods, particularly 72 hours, to accurately assess the forage’s fermentative behavior and nutritional value. This is particularly relevant in tropical livestock systems, where native grasses like Axonopus scoparius are often undervalued due to a lack of scientific evaluation. Therefore, the 72-hour digestibility data provide robust evidence supporting its inclusion in ruminant feeding programs, offering potential to enhance fibre utilisation, feed efficiency, and overall productivity in sustainable livestock systems.

Table 2
Statistical analysis of the correlation and significance of the study.

Incubation period	Correlation	r2	Regression (b)	Intersect (a)	Fisher test
24 h	0.1267c	0.0161	20.9460	− 0.0125	0.5551
48 h	0.3325b	0.1106	31.7404	− 0.0498	0.1124
72 h	0.5289a	0.2797	40.4162	− 0.0852	0.0079

• ^a-c Means with different letter in the same column differ a P value < 0.05.

4. Conclusion

The present study demonstrates that Axonopus scoparius exhibits low but variable in vitro digestibility under Ecuadorian tropical conditions, with statistically significant differences across altitudinal zones and incubation times. A 72-hour incubation period yielded the highest digestibility values, highlighting the forage's potential when given sufficient fermentation time. Although overall digestibility remained below optimal thresholds for high-performance ruminant systems, these results provide valuable baseline data for reevaluating native grass utilization. Improved management and nutritional strategies could enhance its integration into sustainable livestock production, especially in resource-limited settings where resilient, low-input forages are essential.

• Data Availability Statement
  Data are not publicly available due to privacy or ethical restrictions, but can be obtained from the corresponding author upon reasonable request.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Data availability

Data are not publicly available due to privacy or ethical restrictions, but can be obtained from the corresponding author upon reasonable request.

Publication Dates

• Publication in this collection
  18 Aug 2025
• Date of issue
  2025

History

• Received
  16 Apr 2025
• Accepted
  09 June 2025