ORIGINAL ARTICLE

Characterization of grains and panicles quality of Cuban sorghum cultivars harvested at two grain vegetative stages and two harvesting season

Caracterización de la calidad de granos y panículas de cultivares cubanos de sorgos cosechados en dos estados vegetativos del grano y dos épocas de cosecha

Janhad L. Rodríguez-Mendieta,^I V.D. Gil-Díaz,^II L. I. Marrero-Suárez,^I,II A. Castro-Alegría,^I Sandra Hoedtke,^III R. Lima-Orozco,^I,II

ABSTRACT

The effect of harvesting season (HS: rainy vs. dry) and grain vegetative stage (GVS: soft dough vs. hard dough) at harvesting time on grains and panicles quality parameters from three sorghum (Sorghum bicolor (L. Moench)) cultivars (new cultivar: CIAP MC-04-12, subsp. bicolor, race guinea; commercial cultivars: CIAP 2E-95 and CIAP 132R-05, subsp. bicolor, race bicolor) during two years (2011 and 2012) were determined. The GVS at harvesting time affected all studied parameters, while HS at harvesting time affected the dry matter, crude protein (CP), neutral detergent fiber, the slowly digestible starch fraction, organic matter (OM) digestibility and digestible energy (DE). The starch (St) of the new sorghum cultivar was classified as a St of slow digestibility and showed lower proportion of highly digestible St fraction as compared with the commercial sorghum cultivars. The hard dough grains showed the best nutritive value independent of HS (e.g., new sorghum cultivar: 127-130 g CP/kg DM, 673-677 g St/kg DM, 867-884 g digested OM/kg DM and 14.6-14.9 MJ DE/kg DM). In this study grains from new sorghum cultivar have good nutritional value to pigs and provide a basis for further studies as an interesting animal feed alternative, especially for non-ruminants.

Key words: sorghum, grain vegetative stage, nutritive value, grain quality, starch.

RESUMEN

El efecto de la época de cosecha (EC: lluviosa vs. poco lluviosa) y estado vegetativo del grano (EVG: masa suave vs. masa dura) en el momento de la cosecha en los indicadores de calidad de granos y panículas de tres sorgos (Sorghum bicolor (L. Moench)) cultivares (nuevo cultivar: CIAP MC-04-12, subsp. bicolor, raza Guinea; cultivares comerciales: CIAP 2E-95 y CIAP 132R-05, subsp. bicolor, raza bicolor) durante dos años (2011 y 2012) fueron determinados. El  EVG en el momento de la cosecha afectó todos los indicadores estudiados, mientras que en el momento de  cosecha  la EC afectó a la materia seca, proteína bruta (PB), fibra neutro detergente, la fracción de almidón de digestión lenta, digestibilidad de la materia orgánica (MO) y energía digestible (ED). El almidón (A) del nuevo cultivar de sorgo fue clasificado como un A de digestibilidad lenta y mostró menor proporción de fracción A altamente digerible en comparación con los cultivares comerciales de sorgo. Los granos de masa dura mostraron el mejor valor nutritivo independiente de la EC (por ejemplo: nuevo cultivar de sorgo: 127-130 g PB/kg MS, 673-677 g A/kg MS, 867-884 g  MO digerida/kg MS y14.6- 14.9 MJ ED/kg MS). En este estudio los granos del nuevo cultivar de sorgo tienen buen valor nutricional para los cerdos y proporcionan las bases para  estudios posteriores  como una alternativa interesante para la alimentación animal, especialmente para los no rumiantes.

INTRODUCTION

The low yield of cereals in tropical areas (e.g., corn, wheat) limit the livestock production, especially of non-ruminant species, when cereal grains are used as the main component in their feeding systems (Castro 2000). Moreover, the increase of the cereals’ world market price brings the necessity to use feedstuffs from crops adapted to diverse agro-ecological conditions of the tropical areas such as sorghum and rice, that show higher yields and nutritive values compared to not adapted crops (e.g., wheat, maize, barley) under the same conditions. Sorghum (Sorghum bicolor (L. Moench)) is among the cereals that show a good adaptability with acceptable grain yields in drought-prone areas representing a good energy source for pigs (Mushandu et al. 2005). The ICRISAT (2003) reported about a sorghum race (i.e., guinea) that shows drought and water tolerance with high grain yields, resistance to bird damage by adaptation characteristics (i.e., lax panicles and gaping glumes) and acceptable crude protein contents, which is a viable alternative for producing grains in the tropical agricultural systems, especially by small holders. CIAP MC-04-12 (Sorghum bicolor (L.) Moench, subsp. bicolor, race guinea), being a new cultivar that was obtained by genetic selection at the Centro de Investigaciones Agropecuarias (CIAP, Santa Clara, Cuba), therefore requires an evaluation of its nutritional value to determine adequate inclusion levels for the respective animal feeding systems. However, the nutritional value might be affected by the grain vegetative stage (Black et al. 1980) at harvesting time as well as by the harvesting season (rainy and dry season), where most of the crops are negatively influenced in yield as much as in nutritive value (Pérez et al. 2010). In addition, as feed, the sorghum grain digestibility, and consequently its delivery energy, are lower than those of other cereals such as maize, wheat and rice (Shewayrga et al. 2012); for that reason when sorghum grain cultivars are evaluated is necessary to know the energy and digestibility values for its inclusion in feed systems (Noblet and Jaguelin-Peyraud 2007), especially for non-ruminants species (Annison and Topping 1994). The objective of this paper was to research the harvesting time effects on nutritive value of grains and panicles from three sorghum cultivars.

MATERIALS AND METHODS

Plant material: Sorghums were sown in the experimental station of CIAP, Santa Clara, Cuba (Elevation: 100 m a.s.l., latitude: 22º 43´N, longitude: 79º 90´W) at row distances of 0.90 m and at rate of 25 plants/m². Sowing was carried out in different plots (per cultivar, three plots (0.20 ha/plot)/grain vegetative stage/harvesting season in each year) with similar fertility (average ± SE: P₂O₅, 3.47± 0.29 mg/100 g of soil; K₂O, 4.91±0.22 mg/100 g of soil and OM, 1.88±0.08%) and the same soil type (brown calcareous inceptisol; McCune et al. 2011) and crops were neither irrigated and fertilized. Grains and panicles were harvested by hand at two vegetative grain stages (soft dough and hard dough) and in two harvesting seasons [dry season (February for soft dough grain stage and March for hard dough grain stage) and rainy season (August for soft dough grain stage and September for hard dough grain stage)] during two years (2011 and 2012). Average (± SD) precipitation, temperature and humidity during the cropping period of rainy and dry season in 2011 were 182 ±30 mm and 39 ±11 mm, 27.6 ±0.5 °C and 22.1 ±0.9 °C and 80 ±1 % and 75 ±2 %, respectively; for 2012 were 193 ±24 mm and 46 ±14 mm, 28.2 ±0.4 °C and 20.7 ±0.5 °C and 80 ±2 % and 76 ±1 %, respectively.

Treatments and design. A split plot design with three replications per grain vegetation stage was used to compare three sorghum cultivars. They were the main plots, while the subplots were two harvesting times (soft dough grain stage and hard dough stage) per season.

Sampling and proximate chemical analysis: Immediately after harvesting 50 kg of panicles from different areas of each plot were collected, from this a subsample of 40 kg of panicles was used for takeout the grains from panicles to be used in further procedures; the another subsample (10 kg of panicles) was performed to be used in further procedures as whole panicle (without remove grains). These materials collected per each plot were dried at 65 °C during 72 h in triplicate. Afterwards, the dried material was ground to pass a 1 mm sieve and 350 g of grains or panicles stored in glass bottles at room temperature (28 ± 3 °C) before being further analyzed.

In vitro digestibility and energy estimation: The starch (St) contents and their in vitro digestibility were determined in three steps simulating the digestion in mouth, stomach and intestine in a closed system, by measuring glucose at different incubation times (0, 0.5, 1.0, 2.0, 6.0 and 24 h) according to the enzymatic methods suggested by Al-Rabadi et al. (2009). In briefly: 0.5 g of sample were placed in an Erlenmeyer (250 mL of capacity) in which 5 mL of carbonate buffer (39.2 g of NaHCO₃ per liter of distilled water, pH 7.0) containing 11.0 mg α-amylase /mL (enzyme activity of 25 units/mg) were added and well mixed with the sample. This step was followed by the addition of 5 mL of pepsin solution (25 mg pepsin/mL of 0.02 M HCl solution). Hence, the Erlenmeyers were placed in a shaking incubator at 37 °C and 85 rpm during 30 min. After this time 25 mL of sodium acetate buffer containing 2 mg sodium azide per mL (pH 6.0), 5 mL of 0.02 M NaOH and 5 mL of pancreatin and amyloglucosidase solution (2 mg pancreatin and 0.9 mg amyloglucosidase per mL of acetate buffer containing 2 mg sodium azide per mL) were added to the mixture and placed into the shaking incubator at 37 °C (zero hour) and 85 rpm during 24 h, the incubation was stopped at 0.5, 1.0, 2.0, 6.0 and 24 h placing the Erlenmeyer in ice for 5 min to stop enzymatic activity and taking 1.0 mL of supernatant to determine the glucose content by enzymatic method. The kinetic of St digestion was calculated using a non-linear regression model proposed by van Kempen et al. (2010).

In addition, the St was classified in three fractions according to their digestion rate (Muir and O’Dea 1993 and van Kempen et al. 2010): ≤ 120 min, St highly digestible (StHd); > 120 min ≤ 360 min, St slowly digestible (StSd) and > 360 min, St resistant to the digestion (StRd).

The in vitro OM digestibility (OMdv) was assessed according to Noblet and Jaguelin-Peyraud, (2007) and Al-Rabadi et al. (2009). Based on OMdv results the in vivo OM digestibility (OMd) and digestible energy (DE) were estimated (Noblet and Jaguelin-Peyraud 2007) using the equations presented in table 1.

Statistical analysis: To assess the effect of cultivar, harvesting year, harvesting season and grain vegetative stage on the quality and nutritive value of grains and panicles from both sorghums cultivars the general linear model (GLM) analyses were performed with SPSS version 21(SPSS  2012) following the model:

Y_ijk=μ + SC_i=1-2 + HY_j=1-2 + GVS_k=1-2 + HS_l=1-2 + SC×HY + SC×GVS + SC×HS + HY×GVS + HY×HS + GVS×HS + SC×HY×GVS + SC×HY×HS + SC×GVS×HS + HY×GVS×HS + SC×HY×GVS×HS + ɛ_ijk,

with, SC_i=1-2, the sorghum cultivar (CIAP MC-04-12 vs. CIAP 2E-95); HY_j=1-2, harvesting year (2011 vs. 2012); GVS_k=1-2, the grain vegetative stage at the season time (soft dough vs. hard dough); HS_l=1-2, the harvesting season (rainy vs. dry); SC×HY, SC×GVS, SC×HS, HY×GVS, HY×HS, GVS×HS, SC×HY×GVS, SC×HY×HS, SC×GVS×HS, HY×GVS×HS, SC×HY×GVS×HS, the interaction among different factors and ɛ_ijk, the experimental error.

A non-linear regression model (van Kempen et al. 2010) was used to assess the starch digestion kinetics as fallow:

dSt=(A+B×(1–exp(–k_plateau/plateau× t))××(C_plateau/plateau + 1))×10,

with, dSt: starch hydrolysis (g/kg starch); A, digested starch (glucose×starch conversion factor (0.9)) expressed as g per g starch before enzymatic addition; B, starch (glucose×0.9) released by exhaustive digestion expressed as g per g starch; k_plateau, the digestion rate of starch (g/kg starch per hour); plateau, maximal starch (glucose × 0.9) release (A+B) as g per 100 g of sample weight; C_plateau, sigmoidal/shape modifier corrected for plateau effects, and t is the incubation time; 10, conversion factor.

RESULTS AND DISCUSSION

Proximate chemical composition: The GVS (table 2) at harvesting time affected (P < 0.001) the concentration of all studied parameters (DM, OM, CP, EE, NDF, ADF, hemicellulose, cellulose, lignin, glucose and St) in grains from three sorghum cultivars, whereas for the hard dough grain stage showed the best (P < 0.001) concentrations of the referred parameters. The HS only affected (P < 0.05) DM, CP, NDF, hemicelluloses and St, although there was an interaction (P < 0.001) between the HS and the GVS for DM contents. In addition, the HY had influence (P < 0.05) on the DM, OM, cellulose, glucose and St of the grains from three sorghum cultivars. However the CIAP MC-04-12 sorghum cultivar show higher (P < 0.001) concentration of CP, EE, glucose and St as well as lower (P < 0.001) NDF, ADF, hemicellulose, cellulose and lignin than both commercial sorghum cultivars.

Regarding the panicles from three sorghum cultivars (table 3) the grain vegetative stage only had no effect (P > 0.05) on OM and lignin. In our study, the CP content of panicles from CIAP MC-04-12 sorghum cultivar showed acceptable values with the best CP content in the soft dough grain stage compared with panicles in the hard dough grain stage (table 3). Besides, the DM, CP, EE and cell wall contents of panicles from three sorghum cultivars were affected (P < 0.01) by harvesting season (table 3). Sorghum cultivar affected all parameters studied (P < 0.001) except (P > 0.05) to DM and OM; where panicles from CIAP MC-04-12 sorghum cultivar show higher (P < 0.001) contents of CP, NDF, ADF, hemicellulose, cellulose, glucose and St than panicles from both commercial sorghum cultivars.

Digestibility and energy. The in vitro digestibility and energy contents as well as their estimated values for the in vivo digestibility are presented, for both grains and panicles from three sorghum cultivars harvested at different GVS and HS in Table 4 and 5. The digestibility parameters for OM (OMdv and OMd) and St (StHd, StSd, StRd and kplateau), as well as DE of both grains and panicles from three sorghum cultivars were affected (P < 0.01) by SC and GVS at harvesting time (tables 4 and 5).

The OM of both grains and panicles was more digestible and showed a higher (P < 0.05) energy concentration when were harvested at the hard dough grain stage during the rainy season (Tables 4 and 5). It seems that those results are influenced by the higher grain quality under these crop conditions (e.g., higher content of CP, St and EE).

Proximate chemical composition: Sorghum grain quality is affected by several factors, among them genotype, soil type, fertilization, vegetative stage at harvesting and climate, which affect both the chemical composition and the nutritive value (Jahadzad et al. 2013). In our experiment was fixed the same soil type and similar fertility to reduce those effects on the results and can to accurate better the effect of Sorghum cultivar, harvesting season and grain vegetative stage.

The chemical composition of grains from both Sorghum cultivars (table 2) was inside the range of other Sorghum, but those characteristics of the new sorghum cultivar (CIAP MC-04-12) are closer to the characteristics of grains from hybrid sorghum cultivars [e.g., 105-125 g CP/kg DM, 32.0-37.0 g EE/kg DM and 619-795 g St/kg DM, Liv et al.(2012) and Puga et al. (2013)].

The CP and St contents are strongly related to the sorghum genotype with a range of variation of 114-128 g CP/kg DM and 695-790 g St/kg DM in sorghum cultivars resistant to birds (Hibberd et al., 1982) or 115-165 g CP/kg DM and 600-795 g St/kg DM in cultivars not resistant to birds (Hibberd et al.and 1982; Kriegshauser et al., 2006). Moreover, the CP content of the CIAP MC-04-12 sorghum cultivar showed comparable values (table 2) with other cultivars (110-125 g CP/kg DM; e.g., Cauma 20-20, CG 34/4-3-2 and G 1636) from guinea race grown under the environmental conditions of Burkina Faso (Ouattara et al. 2001) and even higher than other grain sorghum cultivars (90-105 g CP/kg DM; e.g., UDG-110, CIAP 9E-95, CIAP 2E-95, CIAP 132R-05, CIAP 6E-95) harvested in Cuba (Pérez et al. 2010) or used in Venezuela (66-100 g CP/kg DM; e.g., Criollo, Chaguaramas, Himeca, Pioneer) as feedstuff for animals (Ojeda et al. 2010).

Regarding the panicles and according to Johnson et al. (1971) the panicles from bird resistant grain sorghum cultivars showed a higher DM content in the hard dough grain stage (754 g/kg panicle) than in the soft dough grain stage (611 g/kg panicle), but similar cellulose contents between both stages (88.0 and 87.0 g/kg DM, respectively), while the panicles in the soft dough grain stage showed higher CP contents than panicles in the hard dough grain stage (111 and 93.0 g/kg DM). The dry matter and cell wall contents of panicles in our study were affected (P < 0.05) by the harvesting season (table 3). In this respect, the drought stress could be responsible for increased contents of ADF and DM in grasses and Poaceaes (Pérez et al. 2010 and Bean et al. 2013) grown and harvested under drought conditions. In our experiment, the panicles from the CIAP MC-04-12 sorghum cultivar harvested during the dry season (table 3) showed higher (P < 0.001) ADF contents than panicles harvested during the rainy season.

The results obtained on estimated OM digestibility and DE content are comparable with other values reported in experiments with pigs (in vivo methods), in which pigs fed with sorghum or corn diets showed an apparent total tract digestibility of more than 850 g DM/kg DM or 870 g DM/kg DM to sorghum or corn, respectively (Nyannor et al. 2007). In our study, the grains from the new sorghum cultivar (CIAP MC-04-12) showed a total digestibility between 805 and 870 g DM/kg DM which are comparable with the values (790 and 850 g DM/kg DM) of commercial sorghum cultivar. In addition, as compared with soft dough stage, the grains in hard dough stage showed the highest (P < 0.05) OM digestibility in both HS independently of SC. The DE content of the grains (table 4) suggests that it could be a valuable energy source for growing or fattening pigs. The estimated energy contents showed by CIAP MC-04-12 sorghum cultivar is comparable with other results obtained previously by in vivo trials (14.2-16.0 MJ of DE/kg DM) with other sorghum cultivars (Nyannor et al. 2007) or corn distillers supplemented with oil (Ren et al. 2011). Although the panicles from three sorghum cultivars showed a lower DE content than other grain sources and despite its fibrous characteristics, it could be an adequate energy source (Yde et al. 2011 and Shewayrga et al. 2012) to finishing fattening pigs, particularly to regions with a low input of resources and furthermore it could be a valuable energy source to ruminants.

As compared with commercial sorghum cultivars the grains from the CIAP MC-04-12 sorghum cultivar at hard dough grain stage in both HS (rainy and dry) showed a good nutritive value for growing/fattening pigs. This study provide a basis for further studies as an interesting animal feed alternative, especially for pig feeding systems in areas of low grain yields of conventional cereals (e.g., corn, wheat or barley). The panicles compared with grain cereals had a limited nutritive value, especially the energy value, but could be an alternative to fattening pigs in areas with a low input of resources or to feeding ruminants. The starch of CIAP MC-04-12 sorghum cultivar was classified as starch of a slow digestibility.

ACKNOWLEDGEMENTS

This research was supported by Universidad Central “Marta Abreu” de Las Villas (UCLV). Special acknowledgements to the staff from the Experimental Stations in CIAP of the UCLV for the technical assistance during this research.

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Received: June 8, 2015
Accepted: March 11, 2016

Janhad L. Rodríguez-Mendieta, Universidad Central “Marta Abreu” de Las Villas (UCLV), Departamento of Medicina Veterinaria y Zootecnia, Carretera a Camajuaní km 5.5. Santa Clara, Villa Clara .Cuba. Email: raciello@uclv.edu.cu