Open-access Evaluation of sugarcane rind on the nutritional value of ruminant feeding

ABSTRACT

Several studies on the kinetics of sugarcane’s fiber digestion have been published, but, to date, no study has evaluated the influence of sugarcane rind on the digestion of fresh sugarcane by ruminants. This study aimed to evaluate the effects of sugarcane components (rind and pith) on chemical composition, in vitro digestibility, metabolizable energy, and sugarcane quality. A randomized block design was used in a split-plot scheme with five sugarcane genotypes [plot] (RB068027, RB058046, RB987917, RB867515, and RB855536) and three sugarcane components [sub-plot] (rind, pith, and whole cane), Each treatment consisted of four replicates. The chemical composition, in vitro gas production, in vitro digestibility, metabolizable energy, and sugarcane quality were evaluated. No interaction between components and genotypes was observed for the variables analyzed herein. Although the rind had a higher crude protein content, it showed a large amount of insoluble crude protein. The rind had higher fibrous fractions, comprising 87.33 % of the indigestible fraction of the neutral detergent fiber (NDF). The sugarcane rind showed ~ 71.20 % more lignin than the pith tissue. Further, the rind decreased by 6.5 % in vitro dry matter digestibility compared to the whole sugarcane. The in vitro NDF digestibility of the rind was 18.38 % lower than the whole sugarcane. The RB068027 genotype showed the lowest sugarcane quality. Despite the higher content of potentially digestible neutral detergent fiber (pdNDF) in the rind, its high lignin content influences the quality of the final fibrous fractions of sugarcane and negatively impacts the nutritional value. The genotypes do not differ nutritionally, but RB855536 presented higher biomass and energy yields.

Saccharum officinarum L.; digestion; fibrous fractions; forage

Introduction

Sugarcane is grown extensively in America, Africa, Asia, and Oceania on account of its ease of cultivation and outstanding production of green mass, which facilitate its use in ruminant feeding during the dry season (characterized by low rainfall and high temperatures), which results in a shortage of forage (Bento et al., 2018). Thus, sugarcane is an excellent option for farmers as it has advantages such as great nutritional value and forage production per area, concurring with the period of forage shortage compared to tropical forages (Gomes et al., 2016). However, sugarcane production in Brazil focuses on the sugar-energy industry rather than on animal nutrition, making selecting varieties with better nutritional value for animal feeding necessary (Carvalho et al., 2022).

Sugarcane deserves some attention due to its nutritional limitations, such as low protein and mineral levels and low-quality fibrous fractions. Among the nutritional limitations, the fibrous fractions significantly impact feed digestion, and protein and minerals can be corrected by supplements (Gomes et al., 2016). Sugarcane constituents with high lignification are in the strongly recalcitrant rind (Maziero et al., 2013). The tissue architecture of lignin and the suberin lamellae’s aromatic fraction may be a significant physicochemical factor limiting rumen microorganisms’ degradation of sugarcane (Maziero et al., 2013).

Moreover, the existence of a genetic variability effect between sugarcane genotypes on fibrous fraction is a possibility. Fiber-related traits were neglected by selection, resulting in cultivars having more genetic variability available for fiber-related than for sugar-related traits (Cursi et al., 2021). There are many studies on sugarcane’s chemical composition and fiber digestion kinetics, but to date, no study has evaluated the influence of the rind on the digestion of fresh sugarcane. In addition to mechanical protection and water retention, the rind can drain the stored carbon into the stalk, which accumulates sucrose (Wang et al., 2013). Based on the above, it was hypothesized that: 1) the fibrous fractions of the sugarcane pith would have as much impact on the nutritional value as the fibrous fractions of the rind; and 2) there would be a nutritional difference between genotypes. Thus, the present study aimed to evaluate the effect of components (rind and pith) of five sugarcane genotypes on chemical composition, in vitro digestibility, metabolizable energy, and sugarcane quality.

Materials and Methods

Location

The experiment was conducted in Bom Jesus do Itabapoana, Rio de Janeiro, Brazil (21°08’13” S, 41°39’30” W, 85 m altitude). The climate of the northern state of Rio de Janeiro is partial Aw, i.e., humid tropical with rainy summers and dry winters, with an average annual temperature of 23 °C and rainfall of 1,200 mm according to the Köppen-Geiger classification (Alvares et al., 2013).

Area and experimental design

The soil was prepared with plowing, harrowing, and furrowing, according to Portz et al. (2013). Before planting, some soil samples were sent for analysis at the Analysis Center of the Universidade Federal Rural do Rio de Janeiro, Campos dos Goytacazes, Rio de Janeiro. The soil presented the following chemical composition: pH in H2O = 5.8 P (mehlich) = 8 mg dm3; K = 21.5 mg dm3; Na = 0.0 mg dm3; Ca = 1.5 cmol dm3 ; Mg = 0.7 cmol dm3; Al = 0.0 cmol dm3; H + Al = 2.7 cmol dm3; CEC (t) = 1.1 cmol dm3; CEC (T) = 2.2 cmol dm3; SB = 2.2 cmol dm3; BS = 45.6 %; OM = 1.7 %; Fe = 59.5 mg dm3; Cu = 0.3 mg dm3; Zn = 300.6 mg dm3; and Mn = 18.6 mg dm3. The area was fertilized following the recommendations of the Liming and Fertilization Manual of the State of Rio de Janeiro for sugarcane crops (Portz et al., 2013). Four hundred kg ha1 of formulated NPK 08-28-16 was applied. In order to reduce area heterogeneity [soil fertility]) the randomized block used a split-plot design. The factors were arranged per the experimental design as main factor plot genotypes and sub-plot factor components of sugarcane. There were five sugarcane genotypes from the Interuniversity Network for Development of the Sugar-Energy Sector (INDSES), with four replicates for each genotype. The genotypes were RB867515 [G1], RB855536 [G2], RB068027 [G3], RB058046 [G4], and RB987917 [G5]. Three components of sugarcane (rind, pith, and whole cane) were evaluated. Each replicate had four lines, 4 m long, and a spacing of 1.20 m, totaling 19.2 m2 of useful area per replicate.

The harvest was carried out in Aug 2020. Ten whole sugarcanes were harvested from the third row of each plot, and their weight recorded. Next, five stalks were taken for sugarcane quality testing. Five canes were rinded with a spoon so that all the pith in the rind was removed, and the other five canes had the aerial part (whole cane) stripped off.

Chemical composition

The sugarcane samples were taken to the Animal Nutrition Laboratory of the Universidade Estadual do Norte Fluminense (UENF) and separated into rind, pith, and whole sugarcane. They were dried at 55 °C for 72 h, ground in a Wiley mill (R-TE-648, Tecnal) with a 1-mm-sieve, and stored in airtight plastic containers. All samples were analyzed for total dry matter (DM, method 967.03; AOAC, 2019), crude fat (CF, AOAC Method 2003.06; Thiex et al., 2003), ash (method 942.05; AOAC, 2019), and crude protein ([N × 6.25] CP, AOAC Method 984.13 and AOAC Method 2001.11; AOAC, 2019; Thiex et al., 2002). Neutral detergent insoluble fiber (aNDF) was determined using the fiber analyzer (Tecnal TE-149). Sodium sulfite and two standardized heat-stable α-Amylase solution additions were used according to the INCT-CA method F-001/1, as described by Detmann et al. (2012). The acid detergent fiber (ADF) was analyzed also according to the INCT-CA-F-003/1 method described by Detmann et al. (2012) and the lignin (sa) content by Möller (2009). Non-fibrous carbohydrate (NFC) was estimated as NFC (g kg1) = 1000 – CP – CF – Ash – aNDF. The content of neutral detergent soluble (NDS) was obtained by subtracting NDS = 1000 – aNDF. Neutral detergent insoluble crude protein (NDICP) was determined by analyzing the aNDF residues for Kjeldahl nitrogen (Licitra et al., 1996).

For the analysis of indigestible neutral detergent fiber (iNDF), the rind, pith, and whole sugarcane were processed in a Wiley mill with a 4-mm-sieve and stored in 13 × 7 cm nylon bags, 50 µm of pore diameter, a ratio of 25 mg of DM cm2 of the bags’ surface. The bags with samples were tied on a steel chain with a 250 g anchor and introduced into the rumen of four cannulated sheep for 240 h. Next, the material was taken from the rumen and washed under running water until there were no traces of ruminal residue. Subsequently, the samples were dried in a forced-air oven at ± 55 °C for 72 h, and the weight was determined on an analytical scale for further aNDF analysis according to the INCT-CA F-001 method /1, as described by Detmann et al. (2012).

Gas production kinetics, in vitro digestibility, and metabolizable and net energy

Four cannulated sheep were used in this study. The Ethics Committee approved all experimental procedures on the Use of Experimental Animals, protocol 419/2017. The animals weighed 50 kg (standard deviation = 4.1 kg) and were used as donors of ruminal fluid. They were kept in collective stalls with troughs and drinkers. Before ruminal fluid collections, the sheep were adapted to a diet of Tifton 85 hay and concentrate feed (roughage:concentrate ratio [80:20]) with 100 g d1 of sugar for 14 days. After this period, the ruminal fluid collections were initiated moments before daytime feeding, as Yáñez-Ruiz et al. (2016) recommended.

The ruminal fluid (liquid and solid) was collected at several points on the liquid-solid interface of the ruminal environment via cannula using a collecting cup. A buffer solution described by McDougall (1948) was added. Two hundred mg (standard deviation = 10 mg) of rind, pith, and whole sugarcane samples from the five sugarcane genotypes were added in amber penicillin flasks (100 mL) with 20 mL of the previously prepared inoculum [ratio 1:4; ruminal fluid and buffer solution, respectively, according to Goering and Van Soest (1970)]. The free space in the flasks was immediately saturated with CO2. Next, the flasks were sealed and taken to a water bath at 39 °C, where they were shaken during incubation to homogenize the inner content. In vitro incubations were conducted in two consecutive runs, each with the sample in triplicates.

Time profiles of accumulated gas production were obtained using a non-automated device. A 0 to 8 psi manometer (0.05 increments) was attached to a three-way plastic valve. One of the ways was connected to a silicone tube (i.d. 5 mm; 1.5 m in length) with a 20 gauge needle attached to the loose extremity of the tube. The second way was attached to the manometer by a small piece of the silicone tube (i.d. 5 mm; 0.3 m in length) and plastic clamps. The third way was connected by another silicone tube (i.d. 5 mm; 1.3 m in length) to the top of a graduated 25 mL pipette (0.1 mL increments), which had its conical end connected to the stem of a separating funnel (1,000 mL) by the same type of silicone tube (i.d. 5 mm; 0.4 m in length). The funnel and pipette were attached to a metal support stand in a vertical and static position. The connecting system was filled with resazurin solution (0.1 g L1) to the zero mark of the pipette, i.e., it allowed for atmospheric pressure equilibration. The system was cautiously filled to avoid the formation of air bubbles. Pressure and volume were taken at: 0, 1, 2, 3, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36, and 48 h after the ruminal inoculum was added. The pressure and cumulative volume of the fermentation gases were obtained by summing the readings corrected to the mark after zero.

The model used to estimate the cumulative gas production was proposed by Groot et al. (1996):

G = A / ( 1 + ( B c / t c ) ) (1)
R M ( m L h 1 ) = ( ( C × t ( C 1 ) ) / ( B C + t C ) ) (2)

where: G is the amount of gas produced per unit of dry matter (DM) at time t after the incubation started, A, the asymptotic gas production (mg g1 DM), B, the time (h) after incubation in which half of the asymptotic gas was formed representing the speed of gas production, C, a constant that determines the sharpness of the curve change; and RM the maximum gas production rate when the microbial population does not limit the fermentation and digestion is not reduced by chemical or structural barriers of the potentially digestible material.

The determination of in vitro digestibility was focused on a single digestion step of the ruminal fluid, omitting the step with pepsin recommended by Tilley and Terry (1963). The buffer solution was the same as mentioned above. For each sample (rind, pith, and whole cane), triplicates of approximately 200 mg of air-dried samples were weighed and placed in 100 mL amber penicillin flasks with 20 mL of buffer solution and inoculum. The free space in the flasks was immediately saturated with CO2, sealed, and taken to a water bath at 39 °C.

After 48 h of incubation, the flasks were withdrawn from the water bath, washed with hot distilled water (above 90 °C), and the incubated material filtered through quantitative filter paper (55 L s1 m2 air permeability). The resulting material was dried (55 °C 24 h1 followed by 105 °C 16 h1) and weighed to obtain the apparently undigested residue of dry matter (DM). Next, that material was analyzed for in vitro digestibility of NDF implementing the methodology described by Detmann et al. (2012). The potentially digestible fraction was determined by subtracting NDF from iNDF.

The digestibility (D) of DM and NDF was calculated according to the Eq. (3):

D = ( M [ R B ] / M ) × 1000 (3)

where: M = mass of DM or NDF incubated (g); R = DM or NDF residue from incubation (g); B = DM or NDF residue of the blanks (g).

Metabolizable energy (ME) and net energy (NE) of the rind, pith, and whole sugarcane of the five genotypes were estimated using the equations by Menke and Steingass (1988):

M E , M J k g 1 D M = 0.157 × G P + 0.0084 × C P + 0.022 × C F 0.0081 × A s h + 1.06 (4)
N E , M J k g 1 D M = 0.115 × G P + 0.0054 × C P + 0.014 × C F 0.0054 × A s h + 0.36 (5)

where: GP is the net gas production over 24 h (mL mg1 DM).

Sugarcane quality

Five culms from each experimental plot were taken to the Coagro (Cooperativa Agroindustrial do Estado do Rio de Janeiro Ltda.) to conduct the technological analyses according to the methodologies suggested by CONSECANA (2006). Technological analyses were performed only for the whole sugarcane.

The automatic hydraulic press method performed the brix and polarization of sugarcane (POL) analyses from the juice (Codistil). Brix (%) was analyzed using a digital refractometer (Acatec RDA8600) with automatic reading and corrected temperature. An automatic saccharimeter was used to determine the POL (Acatec DAS2500). It was calibrated at 20 °C with a wavelength between 587 and 589.4 nm and fitted with a continuous flow polarimetric tube. The percentage of POL was obtained by the following Eq. (6):

POL, % = ( ( 1.0078 × sacc. ) + 0.0444 ) × ( ( 0.2607 ( 0.009882 × % Brix ) ) (6)

The apparent purity of the juice was obtained by the ratio between POL and Brix, according to Eq. (7):

Purity, % = P O L / B r i x × 100 (7)

Total recoverable sugars (TRS) were determined based on Eq. (8):

T R S , t h a 1 200 / 3 × P ) ) = ( ( 10 × S 0.76 × I F 6.9 ) × ( 5 / 3 (8)

where S is sucrose (%), and P represents the purity calculated by the ratio between % POL and % Brix.

The reducing sugars were calculated according to Eq. (9):

R S , % = 3.641 0.0343 × P (9)

Equations (6), (7), (8), and (9) were proposed by CONSECANA (2006).

At the end of the cycle (360 days), the sugarcane was harvested and weighed by cutting two linear meters of the second line of each experimental replicate. Next, the weights of total biomass (stalks, leaves, and straw) were recorded and used to estimate the tons of stems per hectare (TSH) and corrected for DM content, expressed in t ha1of DM.

Statistical analysis

The chemical composition, cumulative gas production, metabolizable and net energy estimates, and in vitro digestibility were compared by Tukey test at 0.05 significance using the SAS MIXED package using REPEATED statement and option = SUBJECT = Block × genotypes for analyzing split-plot design (SAS OnDemand Academics, SAS Institute Inc.). No interaction was observed between genotypes and components in the analyzed variables. Thus, the genotype was tested with residue (a [numerator degree of freedom = 4 and denominator degree of freedom = 42]) and the components with residue (b [numerator degree of freedom = 2 and denominator degree of freedom = 42]).

The following statistical model was used:

Y i j k = μ + α i + b k + α b i k + β j + α β i j + e i j k

where Yijk is the value observed for the variable under study referring to the k-th replicate of the i-th sugarcane genotype in the j-th component (whole sugarcane without aerial part; sugarcane without rind, and only the rind); μ, the mean of all experimental units for the variable under study; αi the effect of the sugarcane genotype with i = 1,2,3,4,5; bk the random effect of the k-th block on the observation, αbik the residue (a) associated with the plot; βj the effect of the component with i = 1,2,3; αβij, the interaction between sugarcane genotypes and components, and eijk, the residue (b) associated with the split-plots.

Sugarcane biomass and quality were compared by Tukey test at 0.05 significance using the SAS GLM package (SAS OnDemand Academics, SAS Institute Inc.). The following statistical model was used:

Y i j = μ + α i + b j + e i j

where Yij is the value observed for the variable under study referring to the k-th replicate in the i-th sugarcane genotype, µ, the mean of all experimental units for the variable under study, αi, the effect of the sugarcane genotype with i = 1,2,3,4, bj, the random effect of the j-th block on the observation, and eij, the error associated with observation Yij.

Results

Chemical composition

There was no interactive effect (p ≥ 0.05) between components and genotypes on chemical composition (Tables 1 and 2). In the genotypes, G4 presented lower contents for CP (p = 0.042) and CF (p = 0.035) than G2, but it did not differ from the others (Tables 1 and 2). As for the components, although the rind had a higher CP content (p < 0.001), it had a large amount of NDICP (p < 0.001), approximately 34.55 % (10.19/15.57) more than the whole sugarcane and 55.10 % more than the pith. The CF content was also higher for the rind than the whole sugarcane (p < 0.001), approximately 33.88 % more and 72.54 % more than the pith (Tables 1 and 2). However, the rind had lower DM (p < 0.001) and NFC (p < 0.001) content compared to the pith. Ash contents for the rind were higher (p = 0.003) than the pith, but they did not differ from the whole sugarcane (Tables 1 and 2).

Table 1
p-values related to the measured variables analyzed for the effects of the genotypes, components, and genotypes by components interaction.
Table 2
– Effects of components and genotypes on the chemical composition of sugarcane.

Fibrous fractions

There was no interaction effect (p ≥ 0.05) between components and genotypes on fibrous fractions (Tables 1 and 3). The genotypes did not affect (p ≥ 0.05) the fibrous fractions of sugarcane (Tables 1 and 3). However, regarding the components, the rind impacted these fractions, presenting 34.52 % more NDF than whole sugarcane, of which 87.33 % corresponds to the indigestible fraction of NDF (Tables 1 and 3). Furthermore, the potentially digestible fraction of the rind was higher by 52.71 % than whole sugarcane and by 52.68 % more than pith. On the other hand, the NDS contents of the rind were higher (p < 0.001) by 42.21 % than the pith (Tables 1 and 3). Contents of ADF (p < 0.001) and indigestible dry matter (iDM) (p < 0.001) had similar behavior to NDF for the rind, pith, and whole sugarcane. As regards lignin contents, the rind was 71.20 % higher than the pith (p = 0.002) (Tables 1 and 3). The average values of the components for neutral detergent fiber content, indigestible neutral detergent fiber content, potentially digestible neutral detergent fiber content, and in vitro neutral detergent fiber digestibility are presented in Figures 1A-D.

Table 3
– Effects of components and genotypes on the fibrous fractions of sugarcane.

Figure 1
– Evaluation of the fibrous fractions of sugarcane components (rind, pith, and whole cane). A) NDF = Neutral detergent fiber; B) iNDF = Indigestible neutral detergent fiber; C) pdNDF = Potentially digestible neutral detergent fiber; and D) IVNDFD = In vitro neutral detergent fiber digestibility. All expressed in average values across genotypes.

Gas production kinetics, in vitro digestibility, and metabolizable and net energy

There was no effect of interaction (p ≥ 0.05) between components and genotypes on gas production, in vitro digestibility, and energy (Tables 1 and 4). The genotypes did not affect (p ≥ 0.05) the gas production, in vitro dry matter digestibility (IVDMD), in vitro neutral detergent fiber digestibility (IVNDFD), nor the metabolizable and net energy of the sugarcane (Tables 1 and 4). When comparing the components, gas production for the rind was lower (p = 0.001) than that of the pith (Tables 1 and 4) within 24 h of in vitro incubation. However, there was no difference in components regarding sugarcane’s metabolizable (p = 0.085) and net (p = 0.091) energy. Metabolizable and net energy for the rind were lower than the pith, approximately 9.61 and 12.38 % (Table 3), respectively. The rind presented IVDMD 6.5 % lower (p < 0.001) than the whole sugarcane. Additionally, IVNDFD was 18.38 % lower (365.59/447.91) (p < 0.001) than the whole sugarcane (Tables 1 and 4). There was no run effect (p = 0.526).

Sugarcane quality and biomass

Genotype did not affect on TSH (p = 0.173) or biomass (p = 0.771) (Table 5). However, G3 presented lower (p < 0.001) Brix than G1, G2, and G4. POL contents of the G3 genotype differed (p = 0.002) only in G1 and G5. Apparent purity was affected by genotypes (p < 0.001). G5 had 6.34 % more purity than G4. As regards TRS (p < 0.001) and RS (p < 0.001) sugars, only G2 did not differ from G3 (Table 5).

Table 5
– Effects of genotypes on the technological quality of sugarcane.

Discussion

Nutritional quality is essential in choosing a sugarcane variety for ruminant nutrition and productivity. However, one of the limitations of sugarcane in ruminant feeding is the low protein content and fiber digestibility. When the industry selects varieties, little attention is paid to the variables of the plant that affect its nutritional value. This study observed a difference between genotypes for the CP content. G2 was higher (19.8 g kg1) than G4 (14.0 g kg1) (Tables 1 and 2). However, 67.82 % of the CP is in the rind, from which 81.34 % is in the form of NDICP (Tables 1 and 2). Neutral detergent insoluble crude protein represents the B3 fraction of protein fractioning, i.e., the fraction slowly degraded in the rumen because it adheres to the cell wall and is highly escapable from rumen degradation (Sniffen et al., 1992; Lanzas et al., 2008). The CF content was lower for G4 than for the other genotypes (Tables 1 and 2). However, the rind has higher CF content than the pith, and the sugarcane rind’s wax, cutin, and suberin can explain this difference. They are polymerized fatty substances in the cell wall and reduce water loss from the plant (Nawrath, 2002). The wax of the rind has always been attractive for industrial applications, mainly in the cosmetic and pharmaceutical industries (Nuissier et al., 2002). The pith has lower DM than the rind (Tables 1 and 2). This fact is due to the thickness and impermeability of the fatty substances of the rind, thereby preventing water loss. Furthermore, the rind is structurally divided into the outer and inner rind. The outer rind comprises dead cells, providing structural support and protection against mechanical damage and pathogens. The inner rind comprises living tissue, including the phloem, responsible for storing and transporting water and solutes throughout the plant (Rosell et al., 2017). The higher NCF for the pith than the rind is due to the higher sucrose content in the pith. Ash had a higher content for the rind than the pith (Tables 1 and 2).

As regards the fibrous fractions, the rind showed higher levels of fiber than the pith. This result is due to the hemicellulose (NDF minus ADF), cellulose (ADF minus lignin), and lignin that grant greater rigidity, impermeability, and resistance to microbiological and mechanical attacks on plant tissues (Liu et al., 2018). It was observed that the indigestible fraction (iNDF) accounted for most NDF (Figures 1A and B). The indigestibility is probably related to the lignin of the rind and the compact organization of cellulose microfibrils in the hemicellulosic polysaccharide matrix covalently linked to a complex lignin structure (Vega-Sánchez and Ronald, 2010). Even so, lignin is the main component of the plant cell wall and is responsible for resistance to degradation (Bottcher et al., 2013). Thus, pdNDF presented low values, thereby reducing the fibrous fractions’ availability to the ruminal microorganisms (Figure 1C). The iDM showed the same behavior as the iNDF (Tables 1 and 3). The lignin of the rind was 71.21 % higher than the pith. The low lignin content in the pith is due to the negative correlation between lignin and sucrose, which caused a dilution effect. Lignin drastically reduces the efficiency of saccharification in the pith since tissues rich in syringyl (S) are more susceptible to enzymatic hydrolysis than those rich in guaiacyl (G) (Bottcher et al., 2013). The most common monolignols for lignin polymer formation are p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) residues. They are secreted in the apoplast and deposited in the cell wall by extracellular peroxidases and laccases (Bottcher et al., 2013; Dixon and Barros, 2019; Llerena et al., 2019).

Cell wall digestibility is complex and can be influenced by several factors such as porosity, surface area, ratio of lignin monomers, cellulose crystallinity, degree of polymerization that limits the access of cellulolytic enzymes to cell wall polysaccharides, lignin, suberin, and cross-links with hemicellulose (Pu et al., 2013). In the present study, the rind presented lower IVNDFD content (Tables 1 and 4) than the pith, probably due to the higher contents of CF and lignin in the rind, thereby corroborating Pu et al. (2013). For Wilson and Mertens (1995), the rumen microorganisms cannot digest lignin and suberin (plant cell wall biopolymers). It prevents access to the polysaccharide matrix in the cell wall and affects digestibility. On the other hand, the pith showed higher IVNDFD content, which was caused by the higher saccharification, i.e., the number of sugar monomers released through enzymatic hydrolysis of cell wall polysaccharides (Ding et al., 2012). Unlike most grasses, the overall digestibility of sugarcane does not decrease with maturity. Instead, there is a slight increase since the accumulation of soluble cell contents (sugars) offsets the decline in cell wall digestibility. The ability to maintain high digestibility with increasing maturity gives an important advantage to sugarcane as a feed crop, especially in the critical dry season when all other grasses and forages decline in quality and availability (Preston, 1977). Furthermore, the pith also presented higher gas production (24 h) and IVDMD than the rind (Tables 1 and 4; Figure 1D). Another interesting report in this study was the similarity between the rind and pith regarding metabolizable (ME) and net energy (NE). This result is because of the contents of CP and CF in the rind. Even though the rind has a high content of NDICP, the equations for estimating ME and NE do not consider this fraction, only the CP content. Moreover, the equation does not consider the pdNDF levels. The rind, for example, showed a higher content of pdNDF than the pith (Figure 1C). All these factors may have influenced the ME and NE values.

Table 4
– Effects of components and genotypes on the gas production, energy, and in vitro digestibility of sugarcane.

In addition to nutritional characteristics, sugarcane’s production potential and quality are essential for the sugarcane industry and animal nutrition. However, the fibrous fraction (indigestible) affects the best use of sugarcane by animals. Five different genotypes were evaluated in this study, and no differences in productivity (TSH) were observed, although G1 produced 15.36 % less than G2 (Table 5). However, the Brix and POL contents varied between genotypes (Table 5). For Barnes (1974), the higher the Brix degree, the better the nutritional value of sugarcane since approximately 90 % of sugarcane’s dry matter consists of (soluble) carbohydrates. These carbohydrates are divided into fibrous (NDF, mainly) and non-fibrous, represented mainly by sucrose, although this also contains starch and reducing sugars (glucose and fructose). Sucrose is the primary pathway through which the phloem transmits carbohydrates from leaves to the rest of the plant to provide carbon and energy for the growth and accumulation of reserve products (Felix et al., 2009). In sugarcane, ripening is a physiological process that involves the synthesis of sugars in the leaves, translocation of products, and sucrose storage in the stalk (Patrick et al., 2013). Polarization (POL) is an indicator of cane ripeness. The unripe cane has a high content of reducing sugars and color precursor compounds, resulting in low POL values with a dark-colored juice (Pereira et al., 2017). For Rhein et al. (2016), POL is one of the main characteristics of sugarcane quality, along with purity and TRS. In the case of purity, G4 and G5 genotypes showed 80.93 % and 86.47 %, respectively. Purity indicates the sucrose content and is related to the sugarcane’s ripeness. The higher the purity, the greater the sucrose accumulation. As the sugarcane ages, purity tends to decrease and sugar’s color may change, reducing its nutritional value. The goal is to obtain purity greater than 80 % (CONSECANA, 2006). However, the purity of the sugarcane juice can be influenced by mineral and vegetable impurities added to the sugarcane at harvest (Oliveira et al., 2012). Although the genotypes did not affect energy concentration (Tables 1 and 4), the gas production (24 h), ME, and NE showed high mean values in G2 for pith and low values in G4. It was also observed that the POL and purity values did not differ between G2 and G4. However, G2 presented 10.82 % more biomass and 10.15 % more TSH than G4 (Table 4), thereby demonstrating the potential for ruminant nutrition. As regards the reducing sugars (RS), G3 showed a lower value (16.36 %) than other genotypes (but not statistically different from G2), which means this genotype will convert less sucrose into glucose and fructose. The SR tends to follow the POL, increasing with ripening (Durán-Soria et al., 2020). In the present study the SR presented the same behavior as POL (Table 4). The TRS values showed the same behavior as RS (Table 5). The TRS indicates the total sugars in sugarcane, mainly sucrose and reducing sugars, and it is the most critical parameter for the industry and farmers (Costa et al., 2011).

Forage quality is an essential factor for adjusting intake, improving the efficiency of nutrient utilization, and reducing concentrate feedstuffs in the diet of ruminants (Tafaj et al., 2005). Low fiber digestibility is the main limiting factor for high-performance beef or dairy cattle-fed sugarcane-based diets (Corrêa et al., 2003). However, the digestibility of sugarcane does not decrease with maturity because the accumulation of soluble cell contents (sugars) offsets the decrease in cell wall digestibility (Preston, 1977).

Although the rind has a higher content of pdNDF than the pith, the high lignin content in the rind influences the quality of the final fibrous fractions of sugarcane and directly impacts the nutritional value. The genotypes do not differ nutritionally. However, the G2 presents higher biomass and energy yields than the others, making it more attractive in ruminant nutrition.

Acknowledgments

This research was supported by Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), process numbers E-26/010.100974/2018, E-26/010.002458/2019, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

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Edited by

  • Edited by: Vinícius Nunes de Gouvêa

Publication Dates

  • Publication in this collection
    13 May 2024
  • Date of issue
    2024

History

  • Received
    07 Nov 2022
  • Accepted
    29 Nov 2023
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