Entire sugar cane or sugar cane residues for feeding sheep. Chemical composition and in vitro degradability of canes

R Magaña, J Aguirre*, A Aguirre*, S Martínez*, A Gómez*, C Lemus*, R Huerta* and J Ly*

Dirección General de Educación Tecnológica Agropecuaria en Nayarit. Tepic, Nayarit, México
mag_8601@hotmail.com
*Universidad Autónoma de Nayarit. Cuerpo Académico de Producción y Biotecnología Animal. Tepic, Nayarit, México
jorgea@nayar.uan.mx

Abstract

Chemical composition and in vitro degradability of either entire sugar cane or burnt, sugar cane crop residue was determined as influenced by fermentation, additives or none according to a 2 x 3 factorial arrangement with three replications, where the factors were type of sugar cane and sugar cane processing by physical, biological and chemical methods, respectively. The sugar cane cultivar was MEX 69-290, the predominant in the Mexican State of Nayarit, based on its yield potential and local availability.

The results indicate that the nutritive value was affected by the process of preparation of canes. The chemical composition of sugar cane crop residues was improved by fermentation and additives. In vitro rumen degradability as measured for DM digestibility was higher (P<0.05) for intact sugar cane (68.3%) and sugar cane crop residue (75.3%). Sugar cane subjected to a fermentative processes had DM digestibility from 45.4 to 53.0%, but in contrast, showed significantly (P<0.05) higher crude protein content (2.18 to 13.25%) than intact canes (1.50 to 2.60%).

It is suggested that sugar cane and sugar cane crop residues should be satisfactorily employed as feedstuff in integral diets for ruminant animals.

Key words: alimentary processes, chemical composition, crop residues

Introduction

In the dry tropics existing in Nayarit, Mexico, rainy season alternates to a dry period thus determining a season-dependent forage production. In this connection, sugar cane harvest occurs in the dry season. Since this grass if considered an energetic bank, showing an extraordinary production of biomass when utilized for animal feeding, either in an integral form or as crop residue from the sugar industry (Stuart and Fundora 1994), then sugar cane could strategically be managed during the summer period of the year. In this sense, sugar cane could be considered as an alternative for cattle feeding in Nayarit. This is true, if it is taken into account that sugar cane is the main crop to which soil is used, and that Nayarit is in the eight place of Mexico from the point of view of sugar cane cultivation as perennial crop (SAGARPA 2005).

Sugar cane and its industrial residues exhibit a rather particular characteristics regarding its chemical composition, since they have a high content of cell wall fractions, and a high concentration of sucrose and other soluble sugars. At the same time, sugar cane is very poor in protein and minerals (Ruiz et al 2005).

Sugar cane is classified as a bulking feedstuff. On the other hand, it is well known that there are nutritional constraints in sugar cane when offered as the only feed to ruminants. In this connection, it has been reported a reduced feed intake when it is offered alone to animals. However, when combined to other forages and feedstuff, sugar cane can represent a nutritional option of low cost and considerable efficiency in animal production (Muñoz and González 1998). Several alternatives have been suggested to improve the nutritive value of sugar cane for ruminants, either by fermentation, or by using cereals and protein concentrates (Elías et al 1990).

Nevertheless, rations prepared with sugar cane combined as such to cereals and protein concentrates become expensive and determine a feed-depending animal production, therefore preventing its use by ruminant animal producers. According to this consideration, the aim of the present study was to characterize the integral sugar cane and its crop residues from the nutritive point of view, when these products are subjected to physical, chemical and biological processes, in order to explore its use for sheep feeding, which in turn is a small ruminant specie in noticeable growth in Nayarit (SAGARPA 2005).

Materials and methods    

The study was conducted at the Academic Unit of Agriculture, from the Autonomous University of Nayarit, located at the Tepic-Puerto Vallarta road, km 9, in the so-called Matatipac Valley, Municipality of Xalisco, Nayarit. The Unit is at 26º 26’ north latitude, 104º 55’ west longitude, and at a height of 940 m over sea level. Average year round temperature and rain fall are 20.9ºC and 1 250 mm (García 1987).

The green, entire sugar cane and burnt sugar cane, simulating crop residue were from the MEX 69-290 cultivar, which was selected due to its forage yield potential and which occupy the major cultivated surface of Nayarit (INEGI 2003).

Six batches of sugar canes were prepared, and every batch represented one of the six treatments examined according to a 2 x 3 factorial arrangement with three replications, where the factors were type of sugar cane and sugar cane processing by physical (grinding), biological (grinding and fermenting) and chemical (grinding, fermenting plus chemical additives) methods, respectively.  Sugar cane were harvested from an experimental plot according to the technique of Molina et al (1999), by selecting at random the strain showing the major, medium and minor sugar cane density. Five canes from every type of density were cut before burning the plot. The canes were enveloped and tied in order to preserve their identity and afterwards these samples were chopped in fresh state to a particle size of 20 to 50 mm, by a forage chopping machine.

A homogenous mixing was obtained, and three batches of 3 kg each were prepared and weighed. The first batch was dried at 60ºC until constant weight and represented the first treatment, corresponding to the ground sugar cane. The second batch was put into a black, polyethylene container, then compacted and hermetically closed by hand to be stored in a roofed place at environmental temperature (19.5 to 32ºC) during 30 days for allowing a spontaneous fermentation to constitute the second treatment, and was identified as milled and fermented sugar cane. The third sample of cane was placed over a flat, clean and dry surface in order to be mixed with 1.1% urea, 0.5% minerals and 0.5% zeolite in fresh basis respectively. These ingredients were thoroughly mixed and then placed in a polyethylene container and let stored as it was done in treatment 2, to constitute the third treatment, consisting of milled and fermented sugar cane plus additives. The second and third treatments were dried at 60ºC and ground to a particle size of 1 mm after ending the fermentation period. An identical procedure was carried out for preparing three batches in the burnt sugar canes, and these corresponded to the other three treatments, representing the burnt crop residue of sugar cane. Three samples from every batch were taken and these samples constituted the replications in every treatment.

In vitro degradability of sugar canes was determined for DM and organic matter contained in samples taken at random from every batch.  In summary, the method of Tilley and Terry (1963) was implemented for in vitro (rumen) DM and organic matter digestibility, and Menke and Steingass (1988) and Blummel et al (1999) recommendations were taken into consideration. Incubation of samples was conducted under strict anaerobiosis, approximately 0.8 g of sample plus 80 mL of buffered rumen inoculums was used in every assay. The incubation proceeded in a water bath at 39ºC during 120 hours. When the fermentation was stopped, the residue of the incubation mixture was assayed for DM and ash content. The organic matter was assumed to be 100 – percent of ash of samples. As reference material, a sample of aerial, entire maize plants was incubated in meal form, and was subjected to the same experimental conditions existing for sugar cane samples. Data from the characteristics of the fermentation of samples of maize plants were not statistically compared to the others from the six experimental treatments. The characteristics of the aerial part of the maize plant appear in table 1.

Sugar cane samples and incubation residues were analyzed for dry matter and ash following AOAC (1990) procedures, and for NDF, ADF, lignin, cellulose and hemicellulose according to Goering and Van Soest (1970) as modified by Harris (1970) and by our own laboratory, consisting of filtering in vacuo the residues through quantitative filter paper placed in Buchner funnels. The N content of sugar cane samples was determined by the AOAC (1990) recommendations too.

The means were contrasted by the analysis of variance technique following the GLM of SAS (2002). When significant differences (P<0.05) were found, the means were separated by the Tukey test.

Results  

There was no significant (P>0.05) interaction for any of the measurements made in this experiment. Table 2 shows the values for the proximal composition of the sugar canes evaluated. The intact, either green or burn sugar canes contained the highest value of organic matter (P>0.05) as compared to the other types of samples. It was found that the crude protein content was higher (P<0.05) in the three types of burnt sugar canes than the same type of green sugar canes processed in a similar manner.

Overall, it was found that NDF and cellulose values were higher in those batch subjected to fermentation processes (P<0.05), with values as high as 65.07 and 66.28% for NDF in green and burnt sugar canes (table 3).  When either green or burnt ground sugar canes were taken into account, NDF and cellulose data were observed to be the lowest of the different types of sample evaluated. On the other hand, the reverse was true for hemicelluloses content. There was no significant (P>0.05) treatment effect on lignin content of sugar canes, with overall averaged some 6.3%.

With respect to in vitro degradability of DM and organic matter (table 4), it was observed that the highest digestibilities (P<0.05) were encountered in treatments corresponding to intact sugar canes, with respect to the others subjected to a fermentative process.

Overall, in vitro organic matter digestibility values followed to that DM degradation, with highest values found for intact green and burnt sugar canes. Values for in vitro digestibility of DM and organic matter of the aerial part of maize plants (61.85% ± 3.98 and 72.94% ± 1.08) showed middle values between the unprocessed samples of sugar cane and those fermented materials.

Discussion 

Chemical composition of sugar cane

When López et al (2003) studied eight varieties of sugar cane with potential as fodder feedstuff, they found that the MEX 69-290 cultivar had a NDF value as high as 52.75% in integral sugar cane. This figure was higher than that found in the present examination for the same type of cane variety, either in green or burnt state; but, in contrast, lower than the data obtained in those treatments processed by biological and chemical means. Batista et al (2001) reported an average value of 49.14% for NDF in 60 varieties of integral sugar cane of 12 and 18 months of age, which was slightly higher than the integral green or burnt integral cane evaluated in this experiment. 

Batista et al (2001) observed average values of 29.24, 24.48 and 4.16% for ADF, cellulose and lignin in 60 varieties of sugar cane examined in Brazil, which are lower than those reported herein. According to Molina et al (1999) average values corresponding to these three fibre fractions were 34.4, 28.7 and 5.1% in this same order. In the case of samples of integral Mexican cane of the variety named CP 29203, Cuarón and Shimada (1981) observed figures of 46.21, 35.6 and 0.77% respectively, which were higher as compared to that of the current study.

The major crude protein (Nx6.25) content was present in sugar cane when it was subjected to grinding, fermenting and addition of chemicals, 10.93 and 13.25% (see table 2), respectively, with the lowest values corresponding to intact materials, 1.50 and 2.60% respectively. These results are in disagreement to that of Batista et al (2001), who found an average value of 2.46% for crude protein, and to López et al (2003) too, who reported values of 2.46% for this same index when sugar cane tops of the MEX 69-290 cultivar were evaluated. Cuarón and Shimada (1981) claimed that crude protein in CP-29203 sugar cane cultivar was 1.98, 3.35 and 3.40%, when the canes were exposed to physical, grinding, and to ensiling without or with chemical additives. In this same context, Molina et al (1999) also reported that when the Cuban sugar cane cultivar named Ja 60-5  was studied after a second cut and 12 months old, and was subjected to physical, biological and chemical treatments, crude protein value was of 10.3%, thus supporting data from the sugar cane of the present investigation, where similar techniques were employed.

In vitro digestibility of sugar cane

Molina et al (1999) have claimed that sugar cane varieties to be used as animal feed must show a minimum of 50% for DM digestibility. In this evaluation, the MEX 69-290 cultivar even when considered as intact or as a crop residue, had an in vitro digestibility of 68.30 and 75.30% in this same order, although values corresponding to those canes subjected to fermentation and addition of chemicals showed somewhat low in vitro DM digestibility value. Even so, DM digestibility observed in the present evaluation was higher than those reported by Fondevila et al (2002), 42-45% for samples of maize crop residues. In this connection, Juárez et al (2006) reported average values of DM degradability in rumen as low as 34.2% from guinea, bermuda, pangola, Pretoria, buffel and Tanzania grasses. In fact, Muñoz and González (1998) indicated that due to the presence in the sugar cane of soluble carbohydrates, DM digestibility of canes is higher than that of tropical grasses. Interestingly, when Montpellier and Preston (1977) gave derinded sugar cane stalks to sheep, and they found in vivo DM digestibility value as high as 71.3%, which in turn was 18% higher as compared to that of samples of sugar cane containing the rind part of the stalks.

In vitro degradability of DM corresponding to that of sugar cane residues found in the present investigation, were higher than those reported by López et al (2003) for in situ DM digestibility of the same variety, which in that case was 42.85% after 96 hours of incubation, which in turn was higher than those of Aranda and Losada (1980) when sugar cane tops of the B-4362 cultivar was studied in Mexico (37.0%).

In agreement to those data arising from the current investigation, it could be suggested that sugar cane and sugar cane crop residues should be satisfactorily employed as feedstuff in integral diets for ruminant animals.

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Received 18 February 2008; Accepted 29 January 2009; Published 1 February 2009

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