Nutritive Profile, Digestibility, and Carbohydrate Fractionation of Three Sugarcane Genotypes Treated with Calcium Oxide

Abstract

The objective of this study was to evaluate the use of calcium oxide (CaO) on the nutritive profile, digestibility, and carbohydrate fractionation of three sugarcane (Saccharum officinarum hybrids) genotypes: IAC-862480, SP-791011, and CTC-3. Four CaO levels (0, 1.5, 3.0, and 4.5% on a fresh matter basis) were used in a 3 × 4 factorial scheme, whose factors were the three sugarcane genotypes and the four levels of calcium oxide. The chemical composition, carbohydrate fractionation, total digestible nutrients, and in vitro dry matter digestibility (IVDMD) were evaluated. The chemical composition of the treated sugarcane was affected by the genotype and the use of CaO. The CTC-3 genotype showed lower values of crude protein (CP), ether extract (EE), neutral detergent fiber (NDFap), acid detergent fiber (ADF), and phosphorus (p < 0.01) contents when compared to the IAC-862480 genotype. A decreasing linear effect (p < 0.01) of CP, EE, ADF, lignin, cellulose, non-fibrous carbohydrates, and total digestible nutrients was observed with increasing levels of CaO. A quadratic effect was observed for the contents of DM, organic matter, NDFap, and hemicellulose when the sugarcane was treated with CaO (p < 0.05). The treatment of sugarcane with CaO resulted in the reduction (p < 0.05) in the indigestible fraction of sugarcane. The IAC-862480 and SP-791011 genotypes showed a better nutritional profile compared to the CTC-3 genotype. On the other hand, CaO treatment improved IVDMD and decreased the non-digestible fraction of sugarcane.

1. Introduction

Forage production is subject, among other factors, to environmental conditions, especially climatic factors [1]. Under tropical climate conditions, the annual dry season promotes a decrease in the nutritional quality of most forage; as a consequence, there is a severe reduction in the efficiency of animal production [2]. Therefore, in tropical climate conditions, it is necessary to introduce forages adapted to this climate, such as sugarcane, into the animals’ diet, and mix it with other feed sources in the diet, preferably of low economic value, to satisfy the nutritional requirements in the different physiological and growth stages [3], consequently improving productivity.

Sugarcane (Saccharum officinarum hybrids) stands out among the tropical grasses that are utilized as forage, because it has shown to be an economically viable alternative that provides satisfactory animal performance coefficients compared to other roughage sources [4,5].

Numerous genotypes of sugarcane are cultivated today in Brazil, and their choice should be carefully planned because their inappropriate use in a production system may lead to serious problems in the plantation growth [6]. The strategic definition in the choice of genotype represents the possibility of using this forage, with adequate quality, during the forage off-season in the meadows [7]. Genotypes with the greatest forage potential have a fibrous fraction with greater digestibility [8]. The IAC-862480 sugarcane genotype was developed by the Agronomic Institute of Campinas (Instituto Agronômico de Campinas) specifically for animal feeding due to the higher digestibility of its fibrous fraction compared to other genotypes [9].

In addition to the choice of genotype, chemical treatments may allow a more effective availability of soluble carbohydrates (sugars), which can improve the quality of this forage and promote fewer losses [5,10]. In this sense, significantly promising results have been obtained with the use of alkaline additives, such as sodium hydroxide [11,12], calcium hydroxide [13,14], and calcium oxide [15,16,17] as additives, to improve the digestibility or degradability of straw feeds.

The use of alkaline additives in sugarcane modifies the fiber structure, which causes the solubilization of fibrous carbohydrates and increases dry matter digestibility [18,19]. Furthermore, alkaline additives contribute to the control of microorganisms that favor decomposition [20], increasing the aerobic stability of sugarcane.

Our hypothesis was that sugarcane requires alkalinizing chemical additives at a level between 1.5 and 3.0% to be preserved for a period of 24 h and that all of the studied genotypes could have similar responses when in contact with the additive. Thus, the objective of this study was to evaluate the chemical composition, fractionation of carbohydrates, and in vitro dry matter digestibility of three genotypes of sugarcane treated with calcium oxide.

2. Materials and Methods

2.1. Area, Experimental Design, and Tretament Procedure

Three sugarcane genotypes were used: IAC-862480, SP-791011, and CTC-3. Those plant materials were cultivated on the experimental farm of the Instituto Federal de Minas Gerais, Campus Salinas. The experiment was implemented in September 2011, and chemical analyses were performed from April to October 2012 at the Laboratory of Forage Crops and Pastures at the Universidade Estadual do Sudoeste da Bahia, Itapetinga Campus, BA (Brazil).

A completely randomized experimental design was adopted, with a 3 × 4 factorial arrangement, in which the interactions between three genotypes of sugarcane and four calcium oxide (CaO) levels were studied. The sugarcane was collected manually through a cut made 10 cm from the soil plus the removal of straw. The material was then disintegrated in a stationary forage grinder (Nogueira Máquinas Agrícolas, São Paulo, Brazil), approximately 3–5 cm in length. The CaO PA used for analysis was 95% pure, with a maximum of 0.1% iron contaminants, 0.005% heavy metals, 0.05% chlorite, and 0.5% sulfate.

Subsequently, the material was homogenized using an oval-bottomed container with the respective CaO level (0, 1.5, 3.0, and 4.5%, on a fresh matter basis). Ninety-six piles of 300.000 g each (eight per treatment) were formed with the use of an electronic scale (TECNAL, São Paulo, Brazil), which were kept at ambient temperature (21 °C) in the shade for 24 h after the application of CaO. During this period, the temperature was recorded every 12 h inside the heaps (

Table 1. Temperatures obtained in the heaps of sugarcane treated with calcium oxide (CaO), according to the different times after treatment.

Level of CaO (% Fresh Matter Basis)	Genotype	Time (Hours)
		0	12	24
		Temperature (°C)
	IAC-862480	26.3	26.8	34.9
0	SP-791011	25.7	24.9	31.3
	CTC-3	25.0	27.1	34.7
	IAC-862480	33.3	28.8	28.8
1.5	SP-791011	32.6	29.1	28.3
	CTC-3	29.3	29.5	28.0
	IAC-862480	39.9	34.5	30.8
3.0	SP-791011	34.7	32.5	29.6
	CTC-3	33.1	33.5	30.3
	IAC-862480	44.0	34.7	31.4
4.5	SP-791011	34.9	33.5	29.9
	CTC-3	35.2	36.0	31.1

Minimum and maximum ambient temperatures on the evaluation day were 22 and 28 °C, respectively.

).

The sugarcane at 0% CaO did not undergo any dilution, but remained constant for 24 h at ambient temperature, maintaining the same conditions in relation to the other piles. After the treatment period, samples of approximately 1.5 kg were taken from the heaps. Immediately, the samples were placed in plastic bags and stored in a freezer at −20 °C for subsequent analyses.

2.2. Sampling and Chemical Analyses

To evaluate the nutritional composition, the samples were defrosted and pre-dried in a forced-ventilation oven (55 °C; TECNAL, São Paulo, Brazil) for 72 h and then ground in a Willey knife mill with a 1 mm sieve. Analyses of dry matter (DM), ash, crude protein (CP), and ether extract were conducted according to the AOAC methods [21]. The organic matter (OM) content was determined between the DM and ash difference. Acid detergent fiber (ADF) and neutral detergent fiber expressed exclusive of residual ash (NDFa) were analyzed according to Mertens [22]. Hemicellulose (HEM), cellulose (CEL), and lignin (LIG) were estimated according to the equations described by Van Soest and Wine [23].

The in vitro dry matter digestibility (IVDMD) was assayed according to Goering and Van Soest [24]. Total carbohydrates (TCs) and non-fiber carbohydrates (NFCs) were estimated according to Sniffen et al. [25]. The NFCs were considered equivalent to fractions A + B1. Fraction C was defined using the indigestible neutral detergent fiber after 288 h of in situ incubation (method INCT-CA F-009/1) [26]. Fraction B2, which corresponded to the available fiber fraction, was obtained as the difference between NDF and fraction C. To calculate the total digestible nutrients (TDN), the prediction equations suggested by NRC were used [27].

Calcium and phosphorus were analyzed at the Laboratory of Plant Tissue Analysis of the Executive Committee for Cocoa Crops Planning (Comissão Executiva de Planejamento da Lavoura Cacaueira, CEPLAC; Ilheus-BA). Using a mixture of perchloric and nitric acid (1:2), the plant material was digested. Immediately, the phosphorus (P) content was determined using a colorimetric method read in a spectrophotometer (Thermo Fisher Scientific, São Paulo, Brazil), and the calcium (Ca) content was determined by an atomic absorption spectrophotometer (Thermo Fisher Scientific, São Paulo, Brazil) with an air–acetylene flame [28].

2.3. Statistical Analyses

The data were subjected to analysis of variance (two-way ANOVA) in a completely randomized design. The data from the CaO levels were analyzed using the PROC MIXED command of the Statistical Analysis System, version 9.2 (SAS Company, Cary, NC, USA). The effects of the CaO levels were studied using linear and quadratic polynomial contrasts, adopting 0.05 as the critical level of probability. Regression models were selected based on the coefficients of determination and the significance of the regression coefficients. The sugarcane genotypes, after two-way ANOVA analysis, were compared using the Tukey post hoc test, with a statistical significance level of p < 0.05, using the PROC MIXED of SAS 9.4 software (SAS Company, Cary, NC, USA).

3. Results and Discussion

Brazil is the main producer of sugarcane in the world, with a production of 72.5 t ha⁻¹ year⁻¹, and for its versatility in climate adaptation and production, sugarcane shows great potential as forage in animal feed [29]. The nutritional potential of sugarcane gives it the possibility of being used as forage to replace tropical grasses or common forages (such as corn silage) used to feed cattle [30] and small ruminants [31,32] without impacting productivity.

The sugarcane genotypes used in the present experiment showed a similar or superior nutritional composition to some tropical forages [31,33], and although sugarcane’s composition is not as high as that of corn silage, it can be used in mixed diets with other ingredients to improve its physical composition, improve rumination characteristics, and consequently, maintain animal health parameters [32].

There was no interaction effect (p > 0.01) between the genotypes and CaO levels for DM content (

Table 2. Chemical composition, in vitro dry matter digestibility, and carbohydrate fractionation in three genotypes of sugarcane treated with calcium oxide (CaO).

Item 1	Genotype			CaO Level (%)				SEM	p-Value
	IAC-862480	SP-791011	CTC-3	0	1.5	3.0	4.5		Genotype	CaO Level	Genotype × CaO Level
Chemical Composition; g kg−1 (Dry matter basis)
Dry matter	353.8 ab	375.8 a	339.7 b	302.8	356.2	378.6	388.2	1.7	<0.01	<0.01	0.65
Organic matter	868.7	868.9	870.1	964.1	898.7	827.0	787.1	3.0	0.98	<0.01	0.77
Crude protein	44.7 a	37.8 b	37.6 b	45.8	40.9	38.2	35.3	0.6	<0.01	<0.01	0.70
Ether extract	9.9	9.8	9.6	9.9	10.0	9.8	9.3	0.1	0.31	0.02	0.05
NDFa	325.5 a	306.0 b	300.1 b	401.9	338.2	270.4	231.7	1.4	<0.01	0.03	<0.01
Acid detergent fiber	269.0 a	272.7 a	242.8 b	305.4	271.2	244.7	224.6	3.2	<0.01	<0.01	0.13
Hemicellulose	116.0	112.0	115.6	122.0	98.5	93.9	143.9	3.1	0.84	<0.01	0.82
Lignin	47.3	47.2	46.8	59.8	49.9	42.0	36.6	1.0	0.98	<0.01	0.09
Cellulose	214.8 ab	221.8 a	192.2 b	236.4	216.1	201.2	184.8	2.8	<0.01	<0.01	0.41
Non-fibrous carbohydrates	429.6	451.0	469.3	491.7	477.8	438.2	392.2	6.6	0.06	<0.01	0.32
Total digestible nutrients	630.4	644.1	638.1	696.7	657.5	606.2	589.7	5.2	0.56	<0.01	0.56
Total carbohydrates	814.0	834.2	822.8	908.2	847.6	778.9	759.9	5.3	0.31	<0.01	0.41
Phosphorus	3.3 b	4.3 a	3.4 b	3.2	3.8	4.1	3.6	0.2	0.05	0.43	0.20
Calcium	424.1	459.8	424.8	41.4	374.0	554.8	774.7	10.2	0.27	<0.01	0.36
In vitro digestibility; %
Dry matter	71.6	69.1	70.4	66.5	69.8	71.8	73.5	6.1	0.27	<0.01	0.39
Carbohydrate fractionation, %
A + B1	52.6 b	53.9 ab	57.0 a	54.1	56.4	56.2	51.2	5.0	<0.01	0.05	0.09
B2	33.5 b	32.5 ab	29.6 a	30.1	29.5	30.8	37.1	3.6	0.01	<0.01	0.15
C	13.8	13.6	13.5	15.8	14.1	13.0	11.6	3.0	0.78	<0.01	0.25

¹ NDFa = neutral detergent fiber expressed exclusive of residual ash; A + B1 = non-fiber carbohydrates; B2 = available fiber fraction; and C = indigestible fiber fraction. SEM = standard error of the mean. Means followed by different superscript letters in the row differ at 5% probability according to Tukey’s test.

). Differences (p < 0.01) were observed in the DM content between the sugarcane genotypes. The genotype SP-791011 (375.8 g kg⁻¹) showed a higher DM content than CTC-3 (339.7 g kg⁻¹). The observed differences in DM content are related to the nutritional properties of the genotypes in question, given that those were grown in the same place under the same conditions.

A linear increase was found in the DM content (p < 0.01) as the levels of CaO were increased (

Table 3. Regression equations of the parameters evaluated in sugarcane treated with calcium oxide (CaO).

Item	Regression Equation	Determination Coefficient (R2)	p-Value
			Linear	Quadratic
Dry matter	Ŷ = 30.379 + 4.0414 (CaO level) − 0.4853 (CaO level)2	0.99	<0.01	<0.01
Organic matter	Ŷ = 96.6015 − 5.29233 (CaO level) + 0.283636 (CaO level)2	0.99	<0.01	0.04
Crude protein	Ŷ = 4.52347 − 0.228542 (CaO level)	0.98	<0.01	0.42
Ether extract	Ŷ = 1.01219 − 1.29942 (CaO level)	0.66	0.01	0.06
NDFa 1	Ŷ = 40.3573 − 5.10634 (CaO level) + 0.278224 (CaO level)2	0.99	<0.01	0.03
Acid detergent fiber	Ŷ = 30.1849 − 1.79220 (CaO level)	0.99	<0.01	0.28
Hemicellulose	Ŷ = 12.3792 − 3.26628 (CaO level) + 0.816358 (CaO level)2	0.96	0.03	<0.01
Lignin	Ŷ = 5.8729 − 5.15095 (CaO level)	0.98	<0.01	0.28
Cellulose	Ŷ = 23.5123 − 1.13127 (CaO level)	0.99	<0.01	0.73
Non-fibrous carbohydrates	Ŷ = 50.0751 − 2.25374 (CaO level)	0.95	<0.01	0.23
Total digestible nutrients	Ŷ = 69.3432 − 2.48284 (CaO level)	0.97	<0.01	0.28
Total carbohydrates	Ŷ = 90.0787 − 3.42543 (CaO level)	0.96	<0.01	0.06
Calcium	Ŷ = 7.91433 + 15.8718 (CaO level)	0.98	<0.01	0.01
In vitro dry matter digestibility	Ŷ = 33.0472 + 1.5262 (CaO level)	0.97	<0.01	0.51
A + B1	Ŷ = 54.0081 + 3.02645 (CaO level) + 0.803745 (CaO level)2	0.98	<0.01	0.23
B2	Ŷ = 30.2280 − 1.94961 (CaO level) + 0.766652 (CaO level)2	0.99	0.77	<0.01
C	Ŷ = 15.6804 − 0.909924 (CaO level)	0.99	<0.01	0.28

¹ NDFa = neutral detergent fiber expressed exclusive of residual ash. A + B1 = non-fiber carbohydrates; B2 = available fiber fraction; and C = indigestible fiber fraction. Statistical significance was accepted at 5% probability according to Tukey’s test.

), which may be linked to the high percentage of DM in the additive, CaO. The results obtained in this study are in line with those observed by Carvalho et al. [34], who evaluated the effect of propionic acid and Lactobacillus plantarum on sugarcane silage with and without CaO and observed that the addition of CaO increased the DM content compared to other treatments. According to Rabelo et al. [35], this fact is related to the dehydration process that occurs in the sugarcane due to the high temperature during the evaluation days, especially after 24 h. Part of this outcome is attributed to the plant respiration process, which consumes soluble carbohydrates and contributes to DM accumulation.

The increase in the DM content was also the result of the addition of CaO; therefore, the increase in mineral matter content proportionally promotes, as a result, the increase in DM content. This is possible because the DM content of CaO is close to 100%. This can be corroborated by the decreasing values observed in the organic matter content and increasing values of calcium.

The organic matter (OM) content between genotypes was similar (p > 0.05), and there was no effect (p > 0.05) of the interaction between the genotypes and CaO levels (Table 2). A quadratic effect was observed (p < 0.05) for OM content according to the CaO levels (Table 3). The reduction in the OM content occurred due to the increase in CaO, which led to a linear increase (p < 0.05) in the ash content in the plant material of the genotypes. The results obtained in the current study are in agreement with those of Rezende et al. [36], who worked with fresh sugarcane that was hydrolyzed with quicklime at different storage times. Although these authors did not determine the concentration of each mineral, they hypothesized that because some minerals (chlorine, sodium, and fluorine) were lost by volatilization, the reaction between sugarcane and quicklime caused a considerable increase in temperature compared to the control treatment.

Furthermore, the decrease in OM content can be correlated with the physicochemical effects promoted by the use of alkaline compounds, such as CaO, to treat plants with a high content of fiber fractions (Lignin and cellulose), such as sugarcane. According to Zhang et al. [37], alkaline treatment promotes the hydrolysis of the lignocellulosic fraction in plants. Therefore, the OM content will decrease because the cellular content will be more available to be lost in the fermentation process, either by enzymatic activities, or by microorganism degradation. Chemically, alkaline treatment promotes the breaking of ester bonds between hemicellulose and lignin, resulting in increased porosity and internal cell surface area [38]. Physically, the rigidity of the fibrous fraction is lost, modifying the order of the fibers and thus exposing the microfibrils [39].

The IAC-862480 genotype, compared to others, presented the highest (p < 0.05) CP content (44.7 g kg⁻¹ DM; Table 2). The SP-791011 and CTC-3 genotypes did not differ from each other (p > 0.05), and both presented approximately 38 g CP kg⁻¹ DM. There was a linear increase in the CP content of sugarcane according to the CaO level (Table 3), which is associated with the addition of CaO and the loss of nitrogen compounds after alkaline hydrolysis.

The reduction in CP levels as a function of the CaO levels that were observed in this study agree with the observations of Rabelo et al. [35], who evaluated the chemical composition of sugarcane hydrolyzed with quicklime and found a linear decrease in this fraction. Regarding the ether extract (EE) content, there was no difference between the genotypes, nor was there an interaction effect between the genotype and the CaO levels (p > 0.05).

There was an interaction effect between the genotypes and CaO levels on NDFa content (Table 2). The visualization of these interactions between the genotypes and CaO levels showed that NDFa levels (Figure 1) were similar in terms of quadratic effects for the IAC-862480 and CTC-3 genotypes, with minimum points at 4.1% and 4.6% CaO, respectively. For the SP-791011 genotype, the maximum point was observed at 1.0% CaO. At 3.0% CaO, the SP-791011 genotype was superior to IAC-862480 and CTC-3 (p < 0.05) (

Table 4. Deployment of the interaction between genotypes according to calcium oxide (CaO) levels.

Level of CaO (% Fresh Matter)	IAC-862480	SP-791011	CTC-3
	Neutral Detergent Fiber 1 (% DM)
0	41.1	39.3	40.2
1.5	35.0	33.9	32.5
3.0	26.3 b	31.1 a	23.7 b
4.5	27.9 a	18.1 c	23.6 b

¹ Neutral detergent fiber expressed exclusive of residual ash. Means followed by different lowercase letters in the row differ at 5% probability according to Tukey’s test.

). With the addition of 4.5% CaO, the IAC-862480 genotype was superior to the others, followed by the CTC-3 and then SP-791011 genotypes (p < 0.05).

The IAC-862480 and SP-791011 genotypes showed similar levels (p > 0.05) of ADF, and both differed (p < 0.05) from the CTC-3 genotype, which showed a lower ADF content than the others (Table 2). ADF, which is composed of cellulose and lignin, represents the fraction of potentially indigestible fiber; therefore, the higher content of this fraction promoted lower fiber digestibility, making it a low-quality feed. The addition of CaO contributed to the linear decrease in the ADF fractions of sugarcane; the addition of up to 4.5% CaO reduced the ADF content by 27.9%. This reduction may have been the result of the expansion of the cellulose, which makes the fibrous fraction of better quality. Van Soest and Wine [24] reported that ADF is the least digestible fraction of the forage cell wall by rumen microorganisms, consisting of lignin and cellulose. Thus, the reduction in this fraction in the composition of sugarcane represents a greater availability of the cell wall and, consequently, nutrients.

In the evaluation of the hemicellulose content, there was no significant difference (p > 0.05) between the genotypes (Table 2). However, this variable responded quadratically to CaO levels, with its lowest value (9.11%) at 3.0% CaO (Table 3). Hemicellulose is a structural carbohydrate that is potentially digestible by ruminal microorganisms, and a higher percentage of this carbohydrate contributes to ruminants having a greater amount of energy. The hemicellulose response can be explained by the breaking of the hemicellulose–lignin ester bonds, which causes the solubilization of the hemicellulose. Evaluating the hydrolysis of sugarcane with quicklime or hydrated lime, Mota et al. [40] observed that there was a decrease in the hemicellulose content of hydrolyzed sugarcane compared to fresh sugarcane.

There were no significant differences (p > 0.05) in the lignin content between the evaluated genotypes (Table 2). The addition of CaO provided a linear decrease in the lignin content (Table 3). The action of alkaline additives is characterized by the solubilization of the fibrous fraction of the grasses, which makes them susceptible to the activity of microorganisms and cellulolytic enzymes from the rumen, thus disposing the content of the cell cytoplasm. Carvalho et al. [10] worked with goats fed diets containing sugarcane treated with CaO and observed a 20.4% reduction in the lignin content of sugarcane treated with 2.25% CaO. For cellulose content, the SP-791011 and CTC-3 genotypes showed significant differences (p < 0.05) (Table 2). The lowest cellulose content levels were found in the CTC-3 genotype. A higher percentage of cellulose indicates a greater availability of potentially digestible fibrous carbohydrates. There was a linear decrease in cellulose content as CaO levels increased (Table 3). This reduction was due to the hydrolytic effect of the alkaline additive on the cell wall. When evaluating the nutritional value of sugarcane hydrolyzed with sodium hydroxide or CaO, Ribeiro et al. [13] found, for this last additive, an average cellulose content of 29.0%, which represented a reduction of 17.6%.

Regarding non-fiber carbohydrates (NFCs), there were no significant differences between the genotypes (Table 2). The addition of CaO caused a linear decrease in NFC levels (Table 3). The treatment of sugarcane with 0 and 4.5% CaO provided an increase of 3.6 and 21.3% in the ash content, respectively. This 17.7% increase in ash content resulted in a 10% reduction in NFCs because ash is a component of the calculations that determine NFCs. The lower NFC content reduced the energy availability, which could be verified by the total digestible nutrients observed when the genotypes were treated with CaO.

No significant differences were detected between the genotypes (p > 0.05) for the estimated TDN, but there was a linear decrease as a function of CaO levels. When evaluating the effect of quicklime hydrolysis on the chemical composition of sugarcane, Oliveira et al. [41] observed little variation in TDN content with respect to lime levels and different genotypes. These authors also reported that, in silage, the average TDN was lower, decreasing by 4.56% compared to fresh sugarcane.

Significant differences were found (p < 0.05) in the P contents between the genotypes studied (Table 2). The IAC-862480 and CTC-3 genotypes showed similar phosphorus content values, whereas the SP-791011 genotype presented higher values (p < 0.05). According to Siqueira [42], fresh sugarcane is an unbalanced feed that has a high crude protein content and low levels of minerals such as phosphorus, sulfur, zinc, and manganese. These differences between the genotypes demonstrate the importance of determining the genotype that best meets the nutritional requirements of ruminants; however, in the case of calcium (Ca), no significant differences were found (p > 0.05) between the genotypes (Table 2).

As it is a source of calcium, the addition of CaO linearly increased its content in sugarcane (Table 3). These results agree with those reported by Mota et al. [40], who observed an average Ca increase of 605.88 and 452.94%, respectively, for sugarcane hydrolyzed with quicklime and hydrated lime, compared to fresh sugarcane.

There were no significant differences (p > 0.05) in the in vitro dry matter digestibility between the genotypes (Table 2). In contrast, there was a linear increase in sugarcane IVDMD when CaO levels increased (Table 3). This linear increase was mainly related to the linear decrease in the lignin fraction of the treated genotypes. Therefore, there is a negative correlation between these fibrous fractions and the digestibility and use of nutrients by the animals.

The total carbohydrate (TC) content between the genotypes was similar (p > 0.05), and there was no interaction effect between the genotypes and CaO levels (p > 0.05) (Table 2). A linear effect was also found in the TC content according to the CaO levels (Table 3), and the TC reduction was the result of the increase in ash caused by the addition of CaO. These results are in line with those observed by Oliveira et al. [41], who evaluated hydrated lime as a hydrolyzing agent in sugarcane and found that TC levels decreased when sugarcane was subjected to hydrolysis with hydrated lime.

No significant differences were observed (p > 0.05) for the A + B1 fraction according to CaO levels, which averaged 54.5%. According to Carvalho et al. [43], feeds with a high proportion of A + B1 fraction are considered good energy sources for the growth of rumen microorganisms that use NFCs.

The B2 fraction in the IAC-862480 and CTC-3 genotypes showed significant differences (p < 0.05; Table 2). When evaluating the chemical composition of nine sugarcane genotypes, Melo et al. [44] found B2 values ranging from 31.4 to 38.3%. The IAC-862480 genotype showed the highest B2 content (p < 0.05). This result means that a higher proportion of available fiber (B2) can provide more energy to microorganisms [45] and increase rumen microbial protein synthesis when synchronized with dietary nitrogen input. Fraction B2 showed a quadratic response to the CaO levels, reaching the trough addition of 0.6% CaO. The highest B2 content was obtained with 4.5% CaO, which demonstrated the hydrolytic effect of this alkaline additive on the forage cell wall.

Regarding fraction C, there were no significant differences (p > 0.05) between the different genotypes of sugarcane evaluated (Table 2). The average fraction C obtained here (13.6%) was close to the range of 12.1 to 14.8% reported by Melo et al. [44], who evaluated the chemical composition of nine sugarcane genotypes. This fraction decreased linearly with the addition of CaO levels (Table 3). The differences in the values of fraction C were related to the concentration of lignin present in the plant, which is a component that decreased linearly with the addition of the alkalinizer. This variation according to the levels of added CaO generated important differences because the C fraction is associated with the digestibility of fibrous carbohydrates.

In the last decades, the global temperature increased 1.5 °C (274.65 K), with respect to the decade of 1980–1990 [46]. This change will promote the cultivation of plants resistant to these climatic conditions, mainly in tropical climates, as well as sugarcane. Furthermore, growth projections estimate that the global human population will reach 10 billion by 2050 [47]. This increase will result in the need for more food sources, among which are products of animal origin (meat, milk, etc.). Taking into account future climatic conditions and population growth, traditional feeds (soybean meal and ground corn) will have their highest commercial value, and pasture production may be affected. Under these conditions, alternative feeds such as sugarcane will have significant potential in animal feed.

4. Conclusions

The nutritional value of sugarcane treated with calcium oxide was higher in the IAC-862480 and SP-791011 genotypes. Considering the use of CaO, the addition of 4.2% CaO (on a fresh matter basis) promoted the highest availability of dry matter, decreasing lignin and cellulose content. This finding indicates the nutritional superiority of these genotypes for use in animal feed. The use of CaO allows the storage of chopped sugarcane for 24 h without affecting its nutritional characteristics.