Nutritional Evaluation of Sugarcane Cultivars for Ruminants

The objective of this study was to evaluate the nutritional quality of twenty-nine cultivars of sugarcane. The design was completely randomized, with twenty-nine treatments (cultivars) and three replicates. The evaluations were performed at 540 days after planting during the phenological stage of maturation of sugar cane. Stalk length, number of nodes per plant, internodes length and stalk diameter were evaluated. The stalk samples were crushed, pre-dried and ground for achievement of chemical analysis, carbohydrate fractionation and in vitro digestibility of dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF). Journal of Agricultural Studies ISSN 2166-0379 2020, Vol. 8, No. 2 http://jas.macrothink.org 692 Data were analyzed by analysis of variance and posteriorly submitted to Scott-Knott test at 5% probability. Regarding biometric measurements the cultivars differed (P<0.05) for the stalk length, but there was no difference (P>0.05) in the number of nodes as well as in the average internode length and stalk diameter. The content of DM, OM, protein, ether extract, NDF and acid detergent fiber showed differences between the cultivars evaluated (P<0.05). Carbohydrate fractionation also differed between cultivars (P <0.05), being that cultivars RB86 7515, RB92 806 and RB03 6091 presented high fraction of rapidly degradable carbohydrates. The highest values of in vitro digestibility of DM and OM occurred for cultivars RB86 7515, RB92 579 and RB03 6091 (P<0.05). Considering the variables analyzed, the cultivars RB03 6091, RB92 579 and RB86 7515 showed greater concentration of rapidly degradable carbohydrates and greater in vitro digestibility of DM and OM demonstrating potential for use in ruminant feeding.


Introduction
Sugarcane is an alternative widely used in the feeding of ruminants and stands out for its high potential in the production of dry matter and energy per hectare, easy cultivation, resistance and conservation capacity in the field (Mello et al. 2006;Oliveira et al. 2012;Costa et al., 2017).
This forage also presents high levels of soluble carbohydrates (Silva et al., 2008) with sugar content of up to 50% of dry matter (Oliveira et al., 2007). However, there are some disadvantages to its use, such as low protein and mineral content and high content of indigestible fiber and lignin (Ezequiel et al., 2005). The fibrous fraction can be 60% indigestible (Fernandes et al., 2003), which causes rumen repletion and reduction of dry matter intake (Siqueira et al., 2012).
Due to these factors, it is indicated that the inclusion of sugar cane in the diet of dairy cows does not exceed 40% of the total dry matter. Sugar cane can be supplied fresh, ensiled or hydrolyzed (Siqueira et al., 2012). In the fresh form, due to the low concentration of protein, usually the sugar cane is mixed with a solution of urea and ammonium sulfate that serve as a source of nitrogen and sulfur, respectively, for the synthesis of microbial protein in rumen (Tiago and Vieira, 2002). When ensiled, the sugarcane fermentation process provides intense activity of epiphytic yeasts, which reduce the nutritional value and increase losses during storage. Thus, sugarcane ensilage requires the use of microbial additives to minimize these losses. In the case of hydrolysis, alkaline agents are added to sugar cane to solubilize the fiber and control unwanted microorganisms. However, the advantages obtained with the increase in fiber solubility are negatively offset by losses of soluble carbohydrates (Siqueira et al., 2012).
An important factor to consider is the use of cultivars having characteristics to allow a good performance to animals. The numerous existing cultivars have quite diverse characteristics, and specifically when intended for animal feed, the main characteristics evaluated are the production, the harvest facility and nutritional quality, observing not only its sugar content, ISSN 2166-0379 2020 but also the fiber quality (Freitas et al., 2006).

Journal of Agricultural Studies
Selecting sugarcane genotypes with lower NDF content and higher NDF digestibility may be a strategy for improving the efficiency of sugarcane-based production systems (Daniel et al., 2016). Thus, the objective of this study was to evaluate the nutritional value regarding bromatological composition, carbohydrate fractionation and in vitro digestibility of dry matter, organic matter and neutral detergent fiber of different sugarcane cultivars and select the best profile for ruminant nutrition.
Prior to the cultivation of sugarcane, the area was in a state of fallow, without any cultivation. Soil analysis was performed to determine its chemical characteristics before the culture implantation (Table 1) and subsequently its results used for soil correction, based on culture requirements.
The climate of the region according to the Köppen climate classification is Cfa type, subtropical humid mesothermal of dry winter, with well-distributed rainfall throughout the year and hot summers. The average temperatures of the coldest quarter ranged between 17 º C and 18 º C and the warmest quarter between 28 º C and 29 º C. The crop was not irrigated, and average annual rainfall for the region ranges from 1,600 to 1,800 mm, with the wettest quarter showing totals ranging from 400 to 500 mm (Caviglione, 2000). Table 1. Chemical characteristics of the soil, in the 0 to 40 cm deep layer, in the area before the implantation of sugarcane cultivars. SB: sum of bases; CEC: Cation Exchange Capacity; V: soil base saturation; The sugarcane cultivars were planted in October, 2013. The field experiment was performed with the intention of multiplying the genotypes, therefore, it was composed of a clonal garden where each cultivar was randomly implanted in one plot of 2.5 x 4 m. The design was completely randomized and the treatments were the twenty-nine sugarcane cultivars:  The cut for laboratory evaluations was made at 540 days of culture implantation, on April 17, 2015, consisting in a plant-cane cicle which coincided with the phenological stage of maturation. Three plants were randomly selected from each cultivar which were manually harvested with a cut close to the soil. The upper part of sugarcane was removed, making the cut in the last visible node, dry leaves were also removed, evaluating stem composition.
The biometric measurements evaluated were: stalk length (SL), stalk diameter (SD,) number of nodes per plant (NN) and average internodes length (IL) using a metric tape and caliper.
Subsequently, plants stalks were crushed and transported to the laboratory, pre-dried in a 55° C forced-air oven and ground in a Willey type grinder (sieve size 1 mm) for further analysis. Dry matter (DM), ash, crude protein (CP) and ether extract (EE) contents were evaluated according to AOAC (1990). Neutral detergent fiber (NDF), acid detergent fiber (ADF) according to Van Soest et al. (1991). The organic matter (OM) content was calculated according to the formula: OM= 100 -% ash.
Carbohydrate fractionation and total carbohydrates were determined according to Sniffen et al. (1992): A: soluble sugars with rapid ruminal degradation; B1: rapidly degradable carbohydrates (starch and pectin); B2: potentially degradable carbohydrates with slow degradation rate; C: indigestible carbohydrates.
In vitro digestibilities of dry matter (IVDMD) and organic matter (IVOMD) were estimated by the technique of Tilley and Terry (1963) and adapted to artificial rumen, developed by ANKOM®, as described by Holden (1999). To determine the in vitro digestibility of neutral detergent fiber (IVNDFD), the methodology described by Goering and Van Soest (1975) was adopted, with samples incubated for 48 hours at a temperature of 39 º C, since pepsin and hydrochloric acid digestion was not performed, then was analyzed the NDF content of the residue (Ankom220 Fiber Analyzer).
The study was carried out in a completely randomized design and the data were submitted to analysis of variance (ANOVA) according to the statistical model: Where: Yij = observed value of the studied characteristic, in treatment i and in repetition j; μ = overall mean; Ti = effect of the treatment i; Εij = error associated with Yij observation. When significant, the means were grouped by the Scott Knott test, considering the level of 5% probability.

Results and Discussion
Regarding biometric measurements (Table 2), the 15 cultivars with the highest values (P <0.05) for the stalk length had average values of 2.78 m while the cultivars with the smallest stalk length had average values of 2.24 m (P<0.05). The stalk size had differences in cultivars ranging from 1.74 m to 3.04 m. In the cultivars RB86 7515 and RB92 579 there were values of 2.53 and 2.11 m respectively, being lower than those obtained by Magalhã es et al. (2018) Journal of Agricultural Studies ISSN 2166-0379 2020 with an average of 3.49 m TC 12 months after planting.
There was no difference (P> 0.05) between the cultivars in the number of nodes as well as in the average internode length and stalk diameter. The variable number of nodes may have a negative correlation with the ease of cutting and digestibility, because this portion has a higher proportion of indigestible fiber (Klein, 2010). Internode length according to Bonomo et al. (2009) is an important characteristic to be considered because it concentrates the highest quantity and quality of soluble carbohydrates. The authors also emphasize that the internode length is a characteristic related to the genotype and may to be influenced by environmental conditions, reducing its size in cases of water deficit.

Journal of Agricultural Studies
ISSN 2166-0379 2020, Vol. 8,No. 2 Dry matter values (Table 3) were between 231.5 g kg -1 (RB86 7515) and 301.5 g kg -1 with the highest values (P<0.05) for the cultivar RB 85 5536. Daniel et al. (2016) evaluated 32 varieties in second cut (ratoon cane) with 12 months after the budding and obtained average values of 325 g kg -1 with minimum and maximum values of 276 g kg -1 and 360 g kg -1 , respectively. Miranda et al. (2015) evaluated three sugarcane cultivars during three harvests and obtained average values of 235.46 g kg -1 , the authors related the low DM content to the high rainfall in the month of harvest (Muraro et al., 2009).
In relation to OM, the highest concentrations were observed for cultivars RB01 6913 and RB85 515, while RB83 5089 presented the lowest concentration (P <0.05). According to Siqueira et al. (2012) sugarcane is a feed with low levels of minerals. Bonomo et al. (2009)  Variations in CP content of cultivars may be due to their intrinsic genetic characteristics, cutting age (Mello et al., 2006) and other factors. Given the low protein values of sugarcane as a forage, supplementation with high protein feed or non-protein nitrogen sources is ideal. According to Segato et al. (2006) sugarcane nutritional restrictions can be minimized by increasing a non-protein nitrogen source in the feed, such as urea, which after ingestion is converted into ammonia and used by ruminal microorganisms for microbial protein synthesis.
Ether extract content varied from 1.2 to 11.2 g kg -1 DM. The cultivar RB03 6091 stood out for the highest concentration of this nutrient (P<0.05), while the cultivars RB86 5230, RB03 6066, RB86 7515, RB96 6928, RB85 5546 and RB85 5036 presented the lowest concentrations. Oliveira et al. (2008)  Neutral detergent fiber concentration was higher for the RB95 6911 cultivar with 510.7 g kg -1 DM (P<0.05). The lowest concentration was 314.2 g kg -1 DM observed for cultivar RB03 6091 (P<0.05). The average NDF levels obtained in the present study (398.2 g kg -1 DM) can be considered lesser when related to the results obtained in the studies of Daniel et al. (2016) and Magalhã es et al. (2018) with 482 g kg -1 DM and 446 g kg -1 DM respectively. According to Van Soest (1994) in general, NDF values in sugarcane are not high, however, the fiber quality is low, and the increase in NDF content may reduce digestibility.
According to Magalhã es et al. (2018) NDF contents lower than 500 g kg -1 may increase sugarcane intake by the ruminant, because lesser NDF content in plant, may correspond to a

Journal of Agricultural Studies
ISSN 2166-0379 2020, Vol. 8, No. 2 higher concentration from cellular content, which is rapidly digestible. In addition, a lesser NDF content may indicate a faster ruminal fermentation rate of cellulose and hemicellulose, due to their lower lignification, and may reduce ruminal repletion, increasing intake and consequently animal production.  ISSN 2166-0379 2020 this fibrous fraction is negatively correlated with the digestibility of the feed. The mean ADF value observed in this study (269.2 g kg -1 DM) were similar to those obtained by Bezerra et al. (2017) who evaluated five RB cultivars with average of 263.4 g kg -1 DM.
Regarding carbohydrate fractionation (Table 4), the cultivar RB03 6066 presented the greatest TC value with 982.9 g kg -1 DM, while the cultivar RB83 5089 showed the lowest value (939 g kg -1 DM; P <0.05). The cultivars RB86 7515, RB92 806 and, RB03 6091 presented high fraction of soluble components (A + B1), with average value of 656.1 g kg -1 TC, while the lowest values were for the cultivars RB72 454, RB03 6066 and RB83 5486 (P <0.05). The A + B1 fraction represents the carbohydrates with greater ruminal degradation, such as soluble sugars and starch (Sniffen et al., 1992) and may positively influence animal performance. The cultivar RB86 7515 is noteworthy because in addition to presenting a higher concentration of the A + B1 fraction, it also had a low NDF content, demonstrating an interesting nutritional value for the feeding of ruminants. Bezerra et al. (2017) Sunahara et al. (2018) the highest concentration of this fraction is related to a high NDF content of the food. In the present study, the general average of fraction B2 was 295.1 g kg-1 CT, similar to the obtained by Cruz et al. (2010) that ranged from 273 to 290 g kg-1 of TC.
The highest values of IVDMD and IVOMD (Table 5) occurred for cultivars RB86 7515, RB92 579 and RB03 6091 (P<0.05). This result can be explained by the lower concentration of indigestible carbohydrates (C fraction) of these three cultivars and by the higher concentration of rapidly degradable carbohydrates (A + B1 fraction) in the case of RB86 7515 and RB03 6091. The lowest IVDMD values occurred for RB72 454 and RB95 6911 due to the high concentration of fraction C of these cultivars and the low content of fraction A + B1, in the case of RB72 454. In the general average, the cultivars evaluated presented IVDMD above 650 g kg -1 DM, higher than those obtained by Bezerra et al. (2017), Oliveira et al. (2007), Silva et al. (2008) and Schmidt et al. (2007). Regarding IVNDFD, 19 cultivars showed higher values, but similar to each other, with an average of 466.0 g kg -1 DM. Intermediate values were obtained for cultivars RB92 5345; RB95 6911; RB85 5113; RB01 6916; RB94 6903; RB85 5453; RB03 6059 and RB92 8064, which presented an average of 407.1 g kg -1 DM (P <0.05). The lowest IVNDFD values occurred in cultivars RB86 5230 and RB83 5054, which presented an average of 312.9 g kg -1 DM. The low IVNDFD of the cultivar RB86 5230 occurred due to the high concentration of indigestible carbohydrates (C fraction), while in the RB83 5054 it may have occurred due to the lower proportion of potentially degradable carbohydrates (B2 fraction). Carvalho et al. (2010) evaluated the composition and digestibility of sugarcane and suggested that from the point of view of ruminant nutrition, fiber digestibility would be a more limiting factor for animal performance than DM digestibility, since the stalk presents a greater value of IVDMD and lesser IVNDFD. The lower digestibility of the fiber is related to its complexation with lignin, which reduces the use by the animal. However, in the present study, the IVNDFD of most cultivars was higher than those obtained by Oliveira et al. (2007) that evaluated the cultivars RB83 5453 and IAC86 2480 and obtained mean values of 348.0 and 393.1 g kg -1 DM, respectively.

Conclusion
Cultivars RB03 6091, RB92 579 and RB 86 7515 stood out for presenting lesser indigestible carbohydrate content, greater concentration of rapidly degradable carbohydrates and greater in vitro digestibility of dry matter and organic matter demonstrating potential for use in ruminant feeding.