Sesame Forage for Ruminants: Effects of Cutting Age and Fertilization Level

1. Introduction

Livestock production systems in tropical regions, particularly in the dry tropics, face limitations due to the marked seasonality of rainfall, which affects forage availability and quality, leading to negative consequences for ruminant productivity [1,2]. In regions with warm ecosystems, such as the climatic conditions of Tierra Caliente, Mexico, these limitations are intensified by irregular precipitation patterns and low soil fertility [3], necessitating the identification of forage alternatives adapted to these conditions.

Sesame (Sesamum indicum L.) is a crop widely distributed in tropical and subtropical regions, primarily cultivated for oil production [4,5]. Globally, its production exceeds six million tons annually, standing out for its drought tolerance and its ability to grow in marginal soils due to its deep root system [6,7,8,9]. These characteristics suggest that sesame could represent a viable alternative as a forage crop in environments with water limitations.

In this context, several studies have highlighted the importance of evaluating non-conventional crops to diversify the feed base for ruminants. Several unconventional species have shown potential as forage crops due to their ability to produce biomass and maintain acceptable nutritional value under tropical conditions [3,10]. However, the use of sesame as a forage crop has been scarcely documented.

The nutritive value of forages is closely related to plant maturity at harvest. As phenological development progresses, the proportion of structural carbohydrates and lignified compounds increases, reducing crude protein concentration and forage digestibility [11,12,13,14]. Therefore, determining the optimal cutting age is essential to achieve a balance between yield and quality.

On the other hand, fertilization is a key factor influencing biomass production and forage chemical composition. Nitrogen and phosphorus application have been shown to improve yield and protein content in several forage crops, thereby increasing their nutritional value for ruminant feeding [15,16,17,18].

Unlike staple crops such as maize and sorghum, which commonly receive recommended fertilizer applications, sesame in small-scale dry tropical systems is often cultivated under low-input conditions or even without fertilization. This practice limits productivity and highlights the need to evaluate fertilization strategies specifically adapted to this crop [5,7].

Despite the agronomic relevance of sesame, there is limited information regarding its use as a forage crop, particularly under dry tropical conditions. In addition, few studies have comprehensively evaluated the effects of cutting age and fertilization level on forage yield, chemical composition, energy value, quality indices, nutrient productivity per unit area, and their potential for silage production. Since forage conservation through ensiling is a key strategy to overcome seasonal feed shortages in tropical livestock systems [19,20], understanding the nutritional and fermentative characteristics of sesame forage is important for its potential utilization in ruminant feeding during the dry season.

The objective of this study was to evaluate the effect of fertilization level and cutting age on the yield, nutritional characteristics, and nutrient productivity of sesame forage (Sesamum indicum L.) grown under dry tropical conditions.

2. Materials and Methods

2.1. Description of the Experimental Area

The crop was established during the rainy season from August to October 2023 in an experimental area of the Faculty of Veterinary Medicine and Animal Science No. 1 of the Autonomous University of Guerrero, Mexico, located at 18°20′30″ north latitude and 100°39′18″ west longitude, at 250 m above sea level. The experimental field had a nearly flat topography with sandy loam soil (sand: 77.32%, clay: 12.68%, silt: 10%), bulk density of 1.12 g cm⁻³, slightly acidic pH (6.2), electrical conductivity of 0.05 dS m⁻¹ (very low salinity), and moderate organic matter content (1.4%) [21,22]. Temperature, evaporation, and precipitation were recorded by the Ciudad Altamirano Meteorological Station, Guerrero (2444), of the National Meteorological Service during the crop period (Table 1).

2.2. Experimental Design and Treatments

A split-plot design arranged in randomized complete blocks with three replications was used. The main plot (30 × 40 m = 1200 m²) corresponded to fertilization levels (50 and 150 kg ha⁻¹), while the subplot corresponded to cutting ages (58, 65, and 72 days after sowing). This structure facilitated fertilizer application logistics under field-scale conditions.

Within each experimental unit (subplot), 10 observational units (hills) were selected using zigzag random sampling, excluding a 3 m border strip. For statistical analysis, hill data were averaged by subplot to form 18 independent experimental units, ensuring independence of errors.

2.3. Crop Establishment and Management

The land was prepared using conventional tillage practices, including harrowing and furrow formation spaced 0.75 m apart. The sesame variety ‘Cremoso’ (Felicidad TC) was used. Sowing was performed manually in hills spaced 0.50 m apart. Seeds were placed at a depth of 2 cm and, before sowing, were treated with thiodicarb at a rate of 1 L per 45 kg of seed to prevent soil pest infestation.

At 10 days after sowing (DAS), all plots received basal fertilization consisting of 25 kg ha⁻¹ of 18-46-00 and 25 kg ha⁻¹ of 46-00-00 (N and P₂O₅: 16 and 5.01 kg ha⁻¹), simulating traditional or low-fertilization management. Differential management was established at 30 DAS through a second application of 50 kg ha⁻¹ of 18-46-00 and 50 kg ha⁻¹ of 46-00-00 only in the high-intensity treatment, reaching a total application of 150 kg ha⁻¹ of fertilizer (N and P₂O₅: 48 and 15.04 kg ha⁻¹) during the crop cycle, ensuring crop nutritional requirements.

Pest control was carried out at 25 DAS using triflumuron (1.25 L ha⁻¹), and foliar fertilizer (20-30-10) was applied at a dose of 1 kg ha⁻¹. Weeds were controlled manually using a traditional “tarecua” (a flat, sharp iron sheet anchored to a wooden handle) at 15 and 30 DAS.

2.4. Forage

For sampling, 10 observational cutting units (plants/hills) were selected for each experimental unit (subplot). The forage was manually cut at a height of 10 cm above ground level to prevent sample contamination with soil particles. From each sample, the number of plants per site (NP hill⁻¹) was determined by direct counting. Immediately afterward, the sample was weighed in the field to determine fresh biomass yield (FBY, kg ha⁻¹). Subsequently, the sample was transported to the laboratory and dried in a forced-air oven at 55 °C until constant weight was achieved. The dry matter (DM, %) was determined as the percentage ratio between the dry weight and the fresh weight of the material. The dry matter yield (DMY, kg ha⁻¹) was calculated by multiplying FBY by the DM percentage of each sample. Finally, the absolute growth rate (AGR, kg ha⁻¹ d⁻¹) was determined by dividing the DMY by the chronological age of the forage at the time of each cutting (58, 65, and 72 days). All yield and growth parameters were subsequently extrapolated to a total area of one hectare.

2.5. Chemical Analysis

Dry forage samples from each experimental unit were ground using a Wiley mill (1 mm screen) and analyzed at the Animal Nutrition and Biochemistry Laboratory of the Faculty of Veterinary Medicine and Animal Science of UNAM. Crude protein (CP, %: N × 6.25), ether extract (EE, %), and ash were determined following AOAC procedures [23]. Neutral detergent fiber (NDF, %), acid detergent fiber (ADF, %), and acid detergent lignin (ADL, %) were quantified as described by Van Soest et al. [13].

Non-fibrous carbohydrates (NFC, %) were estimated as follows: NFC = 100 − (CP + EE + ASH + NDF). Calcium (Ca, %) and phosphorus (P, %) were determined according to AOAC methodology [23]. Total digestible nutrients (TDN, %) were estimated using the summative equation based on digestibility coefficients derived from the National Research Council system [24], following the approach described by Weiss et al. [25]: TDN = (CP x 0.72) + (EE x 0.9 x 2.25) + (NDF x 0.4) + (NFC x 0.9) − 7.

Digestible energy (DE, Mcal kg⁻¹) and metabolizable energy (ME, Mcal kg⁻¹) were estimated from the TDN: DE = TDN × 0.04409 and ME = DE × 0.82. Based on bromatological results, dry matter intake (DMI, % BW), digestible dry matter (DDM, %), relative forage value (RFV), relative forage quality (RFQ), and quality index (QI) were also calculated according to the following formulas [26]: DMI = 120 / NDF; DDM = 88.9 − 0.779 x ADF; RFV = (DMI x DDM) / 1.29; RFQ = (DMI x TDN) / 1.23; QI = (0.0125 x RFQ) + 0.097.

2.6. Nutrient Yield

Nutrient yield (kg ha⁻¹) was obtained by multiplying DMY by the concentration of each nutrient (%). Crude protein yield (CPY), ether extract yield (EEY), total digestible nutrient yield (TDNY), neutral detergent fiber yield (NDFY), calcium yield (CaY), and phosphorus yield (PY) were estimated according to the following general equation: Y Nutrient = (DMY x Nutrient) / 100.

2.7. Statistical Analysis

Data were analyzed using analysis of variance (ANOVA) with a split-plot model, including the effects of block, fertilization (main plot), cutting age (subplot), and the interaction between both factors. Due to the split-plot structure, the fertilization effect was tested against the main plot error (Error A), whereas cutting age and its interaction with fertilization were tested against the residual error (Error B).

When significant differences were detected, Tukey’s multiple comparison test was applied (p < 0.05). Additionally, since cutting age is a quantitative factor, orthogonal contrasts were performed to evaluate linear and quadratic trends. Normality and homogeneity assumptions were verified using Shapiro–Wilk and Levene’s tests (p > 0.05). All analyses were performed using statistical software InfoStat version 2020 [27].

3. Results

3.1. Forage Yield

The NP per hill was not significantly influenced (p > 0.05) by fertilization, cutting age, or their interaction, with an overall mean of 15.45 plants hill⁻¹. In contrast, fertilization significantly affected (p < 0.001) crop yield and growth. The 150 kg ha⁻¹ fertilization level increased FBY, DMY, and AGR by 45.6%, 42.3%, and 42.1%, respectively, compared with the 50 kg ha⁻¹ treatment (Table 2).

Cutting age significantly affected DMY (p < 0.05). A progressive increase in biomass accumulation was observed as crop maturity advanced, with forage cutting at 72 days exceeding that at 58 days by 25.7% (5.32 vs. 4.23 t ha⁻¹). This response was supported by a significant linear effect (p < 0.01), with no evidence of a quadratic effect (p > 0.05).

For FBY and AGR, cutting age showed no significant effects or linear and quadratic trends (p > 0.05).

Finally, no significant interaction between factors (F × A) was detected for any variable evaluated (p > 0.05), indicating that the fertilization effect was consistent across cutting ages.

3.2. Chemical Composition

The chemical composition and fiber components of sesame forage were significantly influenced by fertilization and cutting age (Table 3). Fertilization significantly affected CP (p < 0.001), NFC (p = 0.001), NDF (p = 0.012), and P content (p < 0.001). In particular, the application of 150 kg ha⁻¹ of fertilizer increased CP by 29.2% (10.40 vs 8.05%) and P content by 64.3% (0.23 vs 0.14%) compared with 50 kg ha⁻¹ of fertilizer. In contrast, NFC decreased by 16.6% under the higher fertilization level (24.29 vs 29.14%), whereas NDF increased slightly (49.44 vs 46.61%), indicating a shift in structural carbohydrate partitioning. No significant effects of fertilization were observed for DM, EE, ASH, ADF, ADL, or Ca (p > 0.05).

Cutting age showed a significant effect on multiple variables, including DM (p < 0.001), EE (p < 0.001), ASH (p = 0.006), NFC (p = 0.004), ADF (p = 0.024), and Ca (p = 0.038). DM increased progressively with plant maturity, showing a 17.7% increase at 72 days compared with 58 days (20.42 vs 17.36%). Similarly, EE increased markedly with age, rising from 5.17% to 11.68% (+125.9%), indicating substantial accumulation of energy compounds. In contrast, NFC decreased by 19.5% (29.06 to 23.41%) as cutting age advanced. ADF also decreased by 6.8% (40.65 to 37.88%), whereas ADL showed no significant changes (p > 0.05), indicating that the degree of lignification remained relatively stable throughout the evaluated interval. Ca content showed a moderate increase with age, reaching its maximum value at 72 days (1.36%).

Orthogonal contrast analysis confirmed a significant linear trend for DM, EE, ASH, NFC, ADF, and Ca (p < 0.05), with no evidence of quadratic effects for most variables (p > 0.05), indicating progressive changes associated with crop development.

Finally, no significant effects of the fertilization × cutting age interaction (F × A) were detected for any of the evaluated variables (p > 0.05), suggesting that the effects of both factors were independent and consistent across treatments.

The energy content and quality indices of the forage responded differently to fertilization and cutting age (Table 4). Fertilization did not significantly affect DDM (p = 0.806); however, it did influence TDN, DE, and ME (p ≤ 0.001), as well as DMI (p = 0.011) and the quality indices RFV, RFQ, and QI (p ≤ 0.05). In particular, the application of 150 kg ha⁻¹ of fertilizer reduced DMI by 5.8% (2.43 vs 2.58% BW), as well as RFV by 5.9% (109.91 vs 116.83) and RFQ by 9.4% (116.36 vs 128.54), compared with 50 kg ha⁻¹ of fertilizer. Similarly, the QI decreased by 1.8% (1.67 vs 1.70), indicating a slight reduction in the relative forage quality under higher fertilization.

Cutting age significantly affected energy content and some quality indices. TDN, DE, and ME increased with maturity (p < 0.001), showing increases of up to 14.4% in TDN (63.77 vs 55.75) and 14.4% in ME (2.31 vs 2.02 Mcal kg⁻¹) at 72 days compared with 58 days. In contrast, DMI showed no significant changes (p = 0.381). RFV indices did not show significant differences (p = 0.401), whereas RFQ increased significantly with age (p = 0.004), reaching its highest value at 72 days. The QI index also increased with age (p = 0.003).

Orthogonal contrast analysis revealed significant linear effects for TDN, DE, and ME (p < 0.05), with no relevant quadratic effects (p > 0.05), indicating a progressive improvement in energy content with crop maturity. No significant effects of the fertilization × cutting age interaction (p > 0.05) were observed for any of the evaluated variables, confirming the independence of the factors.

3.3. Nutrient Yield

The nutrient yield of sesame forage was highly influenced by fertilization (Table 5). The application of 150 kg ha⁻¹ of fertilizer significantly increased (p < 0.01) CPY, EEY, TDNY, NDFY, and the mineral yields of CaY and PY. In relative terms, the higher fertilization level increased CPY by 83.5% (580.59 vs 316.40 kg ha⁻¹), EEY by 33.3% (468.05 vs 351.61 kg ha⁻¹), TDNY by 35.6% (3268.62 vs 2411.43 kg ha⁻¹), and NDFY by 50.1% (2743.39 vs 1827.53 kg ha⁻¹). Regarding minerals, CaY increased by 39.7% (69.67 vs 49.87 kg ha⁻¹), whereas PY more than doubled under the high fertilizer dose (12.88 vs 5.75 kg ha⁻¹).

Cutting age also had a significant effect on most nutrient yields. CPY showed no significant differences (p > 0.05), whereas EEY, TDNY, NDFY, CaY, and PY increased with maturity (p < 0.05). The behavior of EEY was particularly notable, as it nearly tripled between 58 and 72 days (218.71 vs 618.47 kg ha⁻¹), representing an increase of 182.8%. Likewise, cutting at 72 days increased TDNY by 44.2% compared with cutting at 58 days (3386.41 vs 2349.01 kg ha⁻¹) and increased NDFY by 26.1% (2584.96 vs 2049.49 kg ha⁻¹). Calcium yield also showed a marked increase of 37.5% (72.15 vs 52.35 kg ha⁻¹), while PY increased by 47.4% (11.31 vs 7.67 kg ha⁻¹).

Orthogonal contrasts confirmed significant linear trends (p < 0.05) for EEY, TDNY, NDFY, CaY, and PY, with no quadratic effects detected (p > 0.05). This indicates a progressive increase in nutrient yield with cutting age.

The fertilization × cutting age interaction was not significant for any variable (p > 0.05), indicating that the positive effect of fertilization on nutrient yield was consistent regardless of the cutting stage.

4. Discussion

4.1. Forage Yield

The results demonstrated a differential response between FBY and DMY as sesame forage advanced through its phenological cycle. While FBY and AGR did not show significant variation between 58 and 72 days, DMY increased substantially during this experimental period. This behavior indicates that, rather than an increase in total biomass, DM concentration increased in plant tissues when maturity progressed [19].

This phenomenon may be attributed to the transition toward reproductive stages, in which deposition of structural carbohydrates such as cellulose and hemicellulose intensifies, along with tissue lignification and reduced water content. This pattern has been widely documented in tropical forages, where ontogenic development increases the proportion of structural components and dry matter [27,28,29]. Under dry tropical conditions, this process also represents an adaptive strategy that favors plant physiological stability under water stress by increasing biomass density per unit volume [2].

The highly significant effect of fertilization on all productive variables confirms the high responsiveness of sesame forage to nutrient availability [6,31,32]. The increase in DMY suggests that nitrogen supply not only stimulates initial vegetative growth but also sustains photosynthetic activity and assimilate partitioning toward structural biomass during advanced crop stages [33,34]. This response agrees with reports in several forage crops where fertilization significantly increases biomass accumulation [16,17,35,36].

The absence of a significant interaction between fertilization and cutting age indicates that both factors act independently, suggesting that forage yield in sesame is primarily conditioned by nutrient availability rather than by the specific cutting age within the evaluated range. This finding has important practical implications because it simplifies agronomic decision-making under field conditions.

Compared with traditional forage crops in the dry tropics, such as sorghum, millet, and cowpea, the DMY values obtained in this study were competitive [37,38], reinforcing the potential of the sesame crop as a viable alternative in systems where water availability and limited inputs constrain the productivity of conventional crops. Unlike these crops, sesame exhibits greater tolerance to drought and low-fertility soils, characteristics that position it as a strategic option for diversifying forage production in marginal tropical regions [6,39].

From an applied perspective, implementing adequate fertilization levels alongside improved agronomic management practices presents a clear opportunity to increase forage production per unit area significantly. Likewise, the progressive accumulation of dry matter with increasing cutting age reinforces the convenience of cutting at intermediate to late stages when the objective is to maximize biomass availability for silage production, thereby contributing to the sustainability of livestock systems in the dry tropics.

4.2. Chemical Composition

Changes in the chemical composition of sesame forage were mainly influenced by cutting age and, to a lesser extent, by fertilization. The 17.7% increase in DM with maturity reflects the progressive reduction in water content and the accumulation of structural compounds, a typical behavior of annual forages [11,29]. However, despite this increase, DM management is identified as the critical control factor for sesame forage preservation. According to McDonald et al. [20], DM levels below 25% result in excessive effluent production, leading to the leaching of soluble carbohydrates and essential minerals, thereby reducing energy value. According to Alonso-Galeana et al. [40], fresh sesame silage presents DM levels close to 21%, which results in an unstable pH (> 5.0); however, pre-ensiling management practices such as wilting or molasses addition not only increase DM content but also raise osmotic pressure, restricting the metabolism of clostridial bacteria and ensuring efficient lactic fermentation [41].

The 29.2% increase in CP with the application of 150 kg ha⁻¹ of fertilizer confirms the central role of nitrogen in photosynthetic efficiency and enhanced foliar protein synthesis, while phosphorus promotes root development and the energy supply (ATP) necessary to optimize protein synthesis [33,34,42]. The obtained values (> 10%) exceed the critical threshold of 7% required to maintain ruminal microbial activity [24,28].

On the other hand, EE increased markedly with maturity (5.17 to 11.68%), associated with the high oil accumulation in seeds, a characteristic observed in other oilseed forages such as Glycine max Merr [43]. Although this behavior increases energy density, it may also modulate methane production [44,45]; however, levels above 7% should be strategically managed in diets to avoid inhibition of fibrolytic microorganisms in the rumen [24]. It is worth noting that the incorporation of sesame oil into ruminant diets may improve the nutritional value of meat through the modulation of unsaturated fatty acids [46,47,48].

The decrease in NFC under the effects of fertilization and maturity is attributed to the metabolic cost associated with the biosynthesis of lipids, proteins, and structural cell wall compounds. These processes compete directly for the same carbon skeletons and energy generated during photosynthesis [49,50]. Although this pattern partially agrees with the resource allocation toward stem lignification described by Sniffen et al. [12] and Johnsson et al. [51], in sesame, the synthesis of structural components is considered necessary to sustain plant architecture and support biomass increase, including the weight of reproductive structures. Nevertheless, the NFC values (23–29%) of this forage are higher than the typical range reported for tropical grasses (10% to 16%), ensuring sufficient substrate for lactic fermentation [18,20,41]. However, to optimize this potential, management practices such as wilting or molasses addition are recommended to ensure accelerated acidification capable of neutralizing the buffering capacity of protein and achieving an optimal pH (< 4.2) [40,52].

The increase in NDF (46–49%) with fertilization suggests greater deposition of structural compounds required to support increased foliage. Nevertheless, these values remain within the range (45–50%) considered optimal for stimulating rumination and maintaining animal health without severely compromising intake [14,53].

Conversely, the linear decrease in ADF with cutting age in this forage differs from the conventional pattern observed in grasses, where the fibrous fraction typically increases with maturity [51,53]. However, this behavior is consistent with reports in other oilseed crops, where the rapid accumulation of lipids (EE) in seeds exerts a dilution effect on cell wall components [8,43]. This phenomenon helps preserve forage quality despite advancing plant maturity.

This qualitative stability is confirmed by the behavior of lignin (ADL), which remained constant regardless of fertilization and cutting age. This finding is highly relevant, since lignin is the main limiting factor of fiber digestibility [10,27]. Its stability indicates that the potentially degradable fraction of the cell wall, specifically hemicellulose, remains accessible to ruminal microbiota [11,28]. This explains why no marked reductions were observed in the forage energy parameters despite advancing maturity and increased structural biomass yield.

Regarding mineral components, Ca increased with maturity, reaching values up to 1.36%, which greatly exceeds the recommended requirements for ruminants, ranging from 0.3% to 0.5% of DM [24,54]. This finding is particularly relevant in dry tropical production systems, where the mineral availability of grass forages is often limiting [55]. Such Ca supply is essential for osteogenesis and neuromuscular function in beef cattle production systems [24]. On the other hand, the phosphorus (P) response to fertilization represented a 64.3% increase, reaching levels higher than those reported for tropical grass pastures. These values exceed the critical threshold (0.20%), the level required to optimize microbial protein synthesis in the rumen and ensure efficient degradation of the fibrous fraction [20]. Thus, the interaction between fertilization and plant ontogeny transforms this forage into a strategic resource that could reduce dependence on external mineral supplements in ex-tensive livestock systems.

In energetic terms, while increasing fertilization (150 kg ha⁻¹) induced a moderate but significant reduction (p = 0.001) in TDN, DE, and ME contents, cutting age showed a positive linear effect (p < 0.001) on caloric content. This finding is of great interest because it differs from the classic pattern of quality decline with maturity [8] and showed competitive values relative to unconventional dicotyledonous forages such as Amaranthus hypochondriacus, Camelina sativa, and Borago officinalis. While these species experience a marked decline in digestibility and energy when transitioning from the vegetative to seed stage [56], sesame forage at 72 days not only maintains its energy density but reaches the highest energy concentrations. Furthermore, this energy profile is notably competitive when compared with some grasses, whose ME declines markedly due to lignification [3,8,10]. Whereas in tropical grasses energy density sharply decreases due to lignification, sesame forage at 72 days presents an ME of 2.31 Mcal kg⁻¹ DM, higher than at previous ages. The energy content of sesame forage across the three evaluated ages, particularly at 72 days, was higher than maintenance thresholds (0.672 MJ kg⁰·⁷⁵) for beef cattle discussed by Cabeza-García et al. [57]. This divergence suggests that lipid accumulation compensates for phenological advancement, optimizing caloric concentration compared with conventional forage species under dry-season conditions.

DMI and quality indices (RFV, RFQ, QI) were sensitive to the evaluated factors. The increase in NDF with fertilization influenced the reduction in DMI, which agrees with the physical fill mechanisms described by Grant [53]. Nevertheless, sesame forage maintained RFQ values between 113 and 128, allowing it to be classified as good-quality forage according to international standards suggested by Moore and Under-sander [26]. Notably, despite the increase in fiber, the RFQ of sesame forage at the mature stage (72 days) was similar to Amaranthus hypochondriacus and superior to Camelina sativa and Borago officinalis at the same phenological stage [56], giving sesame forage a broader and more flexible harvest window without progressively compromising nutritive value.

Overall, these results position sesame forage as a viable alternative to traditional crops such as maize and sorghum in the dry tropics, especially in low-input agronomic systems [17,38]. The combination of adequate protein, energy, NFC, and mineral contents, together with favorable DM evolution, reinforces its potential for silage production aimed at overcoming forage deficits during the dry season.

Finally, the absence of a significant interaction (p > 0.05) between fertilization and cutting age indicates that both factors can be managed independently, simplifying agronomic decision-making. Therefore, optimization of cutting timing should balance yield with the optimal balance among CP, NFC, and EE, factors that will determine both fermentation efficiency and the final nutritive value for ruminants.

4.3. Nutrient Yield

In addition to changes in chemical composition, nutrient yield provides a more integrated perspective of forage value, as it combines both biomass production and nutrient concentration per unit area. In the present study, nutrient yield was influenced by both factors, although with different magnitudes. CPY was mainly determined by fertilization, showing an 83.5% increase under the high fertilizer dose, whereas cutting age had no significant effect. This suggests that protein production per hectare in the sesame crop depends more closely on nitrogen nutrition management than on harvest timing, as reported in other crops [35,36].

In contrast, EEY and TDNY were more strongly influenced by cutting age than by fertilization, a pattern that differs from most forages [14,19]. Notably, EEY nearly tripled (+182.8%) between 58 and 72 days, while TDNY increased by 44.2% during the same period. This result exceeded the increase obtained through fertilization (+33.1% and +35.5%, respectively) and highlights that physiological maturity is the primary determinant of energy density in sesame forage due to its natural capacity to accumulate lipids in the seeds, thereby contributing to a higher energy density compared with conventional tropical forages, as demonstrated in previous studies [58,59].

The increase in NDFY (+50.1%) with fertilization and maturity (+26.1%) reflects greater accumulation of structural biomass, suggesting that fertilization accelerates growth and cell wall deposition in stems [13,29]. Although higher fiber content may reduce percentage digestibility, a high NDFY contributes to total forage availability and the maintenance of ruminal function in grazing- or silage-based systems [53].

Finally, regarding mineral productivity, both fertilization and maturity played a determining role. CaY and PY increased significantly with the high fertilization dose (+39.7% and +124%, respectively), but also showed a progressive increase with cutting age (+37.8% and +47.4%). This dual effect is highly relevant: while fertilization enhances mineral extraction from the soil (N–P synergism), plant maturity promotes greater accumulation of these elements in total biomass, which normally declines with plant age in most tropical forages [20,24]. This behavior positions sesame forage as a dynamic mineral source that, unlike other forages that become “diluted” with aging, improves its Ca and P contribution per hectare as the crop cycle advances, thereby reducing dependence on external supplementation in the dry tropics.

The linear trends observed for EEY, TDNY, NDFY, and CaY confirm a progressive accumulation of nutrients with maturity, without evidence of stabilization within the evaluated interval. Nevertheless, these increases should be interpreted together with the reduction in NFC observed at later stages. Adequate NFC availability is essential to achieve rapid acidification and silage stability [40,41]; therefore, although cutting at 72 days maximizes yield per hectare, earlier harvest times may favor fermentative quality. This behavior suggests a sustained productive potential of sesame forage under dry tropical conditions.

The absence of significant interaction between fertilization and cutting age indicates that the positive effects of fertilization on nutrient yield are consistent across growth stages. This simplifies agronomic decision-making, allowing fertilization and cutting timing to be adjusted independently according to the production objective.

Overall, these results reinforce the potential of sesame forage as a high-yield alternative in tropical systems, where traditional agronomic practices and low fertilization levels represent an opportunity to significantly improve protein, energy, fiber, and mineral yields per unit area, according to [4]. In combination with its favorable chemical composition and silage potential, this crop represents a strategic option for improving the sustainability of ruminant production systems in the dry tropics.

5. Conclusions

Fertilization significantly increased dry matter yield and nutrient productivity, improving the availability of protein, energy, fiber, calcium, and phosphorus per unit area. Cutting age influenced nutritional composition by promoting the accumulation of ether extract, fiber fractions, and energy content, while non-fibrous carbohydrates decreased, which may influence silage suitability.

The combination of 72 days of age and 150 kg ha⁻¹ of fertilizer maximized forage yield and nutrient production per hectare. Overall, these results support the use of sesame forage in livestock systems of the dry tropics, provided that fertilization management and harvest timing are optimized to balance yield, nutritional quality, and conservation suitability. Further research evaluating digestibility, animal performance, and silage potential of sesame forage would help better define its role in ruminant feeding strategies.