TECHNICAL NOTE

In vitro gas production of two new varieties of sugar cane (Saccharum spp. C97-366 and C99-374), selected for forage

Producción de gas in vitro de dos nuevos cultivares de caña de azúcar (Saccharum spp. C97-366 y C99-374) seleccionados para forraje

R.M. Pedraza,^I Y. Fernández,^II Ailsa Llánes,^II Cecilia E. González,^I Marlene León,^I

ABSTRACT

This paper presents dynamics and parameters of in vitro gas production of integral forage of two new cultivars of sugarcane (Saccharum spp., C97-366 and C99-374.), selected for forage, and compared with a control (My5514 commercial variety). Integral forage samples were analyzed, according to a completely randomized design, at eleven months of regrowth with the use of the technique of in vitro gas production. New varieties showed higher gas production (P <0.05) than My5514 at 48, 72 and 96 h of incubation, without significant differences among them. Gas production parameters, lag phase and gas production potential (b) ranged from 2.48 to 3.27 h and 32.7 to 36.6 mL, respectively. Gas production speed (c) ranged from 0,023- 0,024 h-1. The two new cultivars had generally better in vitro digestibility than the control.

RESUMEN

Se presenta la dinámica y parámetros de producción de gas in vitro del forraje integral de dos nuevos cultivares de caña de azúcar (Saccharum spp., C97-366 y C99-374), seleccionados para forraje y comparados con un control: el cultivar comercial My5514. Se analizaron, según un diseño completamente al azar, muestras del forraje integral a los once meses de rebrote con utilización de la técnica de producción de gas in vitro. Los nuevos cultivares mostraron mayor producción de gas (P < 0.05) que My5514 a las 48, 72 y 96 h de incubación, sin diferencias significativas entre ellos. Los parámetros de producción de gas, fase lag y potencial de producción de gas (b), oscilaron entre 2.48 – 3.27 h y 32.7 – 36.6 mL, respectivamente. La velocidad de producción de gas (c) fluctuó entre 0.023– 0.024 h-1. Los dos nuevos cultivares tuvieron, en general, mejor digestibilidad in vitro que el control.

INTRODUCTION

Traditionally, selection of sugarcane cultivars for forage begins with the evaluation of phenological and nutritional characteristics, mainly in vitro and in situ, of cultivars selected for sugar production. However, the sugarcane selection procedure for sugar industry discards candidates who do not show a prominent development of stems in relation to the number of leaves. The Estación Territorial de Investigaciones de la Caña de Azúcar (ETICA) in Florida, and the University of Camagüey, both in the province of Camaguey, Cuba, developed a joint study with two new sugarcane cultivars for forage. The study began with the selection procedure established for obtaining sugarcane commercial cultivars for sugar production (Jorge et al. 2011), with the main difference that, after hybridization, those individuals with more potential to produce leaf-shaped forage, and no sugar, were rejected.

As part of the experiments, 106 candidates were evaluated, of which two showed the best phenological characteristics, lower content of total solids, leaf:stem relation and resistance to pests, diseases and water stress. Later, other indicators were studied in the field (Fernández 2015, Llanes 2015) like their phenological characteristics and biomass production, acceptance by the animals and in vitro digestibility using gas production technique, proposed by Menke and Steingass (1988), widely recognized as a useful tool to provide nutritional criteria for ruminants. This technique, like other methods of in vitro and in situ digestibility, is a complement to agronomic studies for selection of grass and forage plants for cattle.

This study shows the dynamics and parameters of gas production, at eleven months of growth, of integral forage from two new cultivars of sugarcane (Saccharum spp., C97-366 and C99-374), compared to My5514 commercial cultivar.

The agronomic experiment that provided samples for this study was conducted in the Estación Territorial de Investigaciones de la Caña de Azúcar (ETICA) in Florida, and the study of in vitro gas production was performed in the University of Camagüey “Ignacio Agramonte Loynaz”, both in Camagüey province, Cuba.

Three cultivars under study (Saccharum spp., C97-366 and C99-374, and My5514 as control) were sown in a brown soil with carbonates (Hernández et al. 1999), in November, 2009, with a plantation of  0.40 m x 1.60 m, according to a random block design with three replications, in plots of 5.5 m long and 5 m wide. The only fertilization was carried out with a complete formula (NPK) at the moment of sowing and 45 d later, with a total of 180 kg/ha of N, 100 kg/ha of P₂O₅ and 240 kg/ha of K₂O. Establishment cut was carried out at 11 months, in October, 2010. All the field experiment was conducted under dry conditions.

At 11 months of growth, three samples of each cultivar were taken as replication, composed by a stem with leaves and buds cut at soil level, and cut with machetes. Representative samples of both were dried at 65° C in a forced air oven for 48 h. Later, these samples were ground with a hammer mill up to go through a sieve of 1 mm.

In vitro gas production was evaluated with the use of a technique proposed by Menke and Steingass (1988), modified to use bovine feces, recently excreted, as inoculum, according to the description of  Martínez (2008). Crystal syringes, calibrated with 100 mL of capacity, were used (FORTUNA®, HäberleLabortechnik Germany). Samples were analyzed according to a completely random design with three replications.

for t<=L       V = 0

for t>L          V = b*(1-EXP(-c*t))

where:

V – accumulated volume in mL/200 mg of dry sample

t – time in hours

b – volume when t → ∞.

b – specific growth speed of gas volume in the exponential phase

Descriptive indicators were determined. Normality of data of gas volume was analyzed by Shapiro-Wilk test (Shapiro and Wilk 1965), and analysis of variance were conducted every hour of incubation. Differences among means were determined by Tukey test, at P<0.05 (Tukey 1958). All statistic processing was carried out with the SPSS statistical package for Windows, 15.0.1 version (IBM Corporation 2006).

Lee et al. (2014) stated different criteria to select sugar cane cultivars for forage and for its use in grazing. One of the main principles to select sugarcane for forage is the ability to transform sun energy into biomass, mainly as leaves for ruminant feeding, which is the least lignified fraction and with best content of nitrogen. Biomass quality is an important element to consider differences among cultivars to be recommended. This depends on the cultivar, soil, sowing areas, regrowth age, sowing cares (Fabris et al. 2014) and season and time of harvest (Lee et al. 2015). 

Results demonstrated that these two new cultivars produce similar gas volumes at 24 h, and superior to control (My5514), mainly at a higher time of incubation. Studies conducted with these two cultivars state that C97-366 variety reached the best yields of dry matter at 11 months of growth, and all cultivars were well accepted by ovines under taste test (Fernández 2015, Llanes 2015).

Results reached during lag phase (figure 2) were inferior to those reported by Martínez (2008) in a study of 13 tropical forages (two families and 11 genera). These suggest a proper presence of available sugars for microbial growth in those three cultivars. Likewise, potential values of gas production were superior and those of gas production speed were similar to that reported by Martínez (2008). Differences with My5514 cultivar may be determined by lower proportion of stems and higher proportion of leaves that characterize these new cultivars. Lee et al. (2014) state that it is important to improve leaf content because this fraction is the most digestible and with the highest density of nutrients.

Results of dynamics and parameters of in vitro gas production showed that these two new cultivars (C97-366 and C99-374) had better in vitro digestibility than control (My5514).

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Received: 22/02/2016
Accepted: 20/07/2016

R.M. Pedraza, Centro de Estudios para el Desarrollo de la Producción Animal (CEDEPA), Facultad de Ciencias Agropecuarias, Universidad de Camagüey “Ignacio Agramonte Loynaz”, Camagüey 74650, Cuba . Email: redimio.pedraza@reduc.edu.cu