Cuba is considered the main area of speciation of the Antilles. It is an inexhaustible source of phytogenetic resources for different uses under dissimilar ecological conditions. In this context, the Cauto Basin and the Toa are characterized by different edaphoclimatic conditions, from regions with high rainfalls to some of extreme drought, with limitations on soil fertility and negative indicators for agricultural use (Martínez et al. 2017).
The study of new food sources for livestock in vulnerable areas is one of the actions prioritized by our state with the purpose of achieving a harmonious and balanced development with the environment, mainly under biotic and abiotic stress conditions (Soriano et al. 2018). Some studies in recent years have been aimed at determining the nutritional value of phytogenetic resources of interest for ruminants feeding in vulnerable areas (Espinoza et al. 2018 and Sánchez et al. 2018). Progress has also been made in offering information about the nutritional value of the main plant species of interest for animal feeding (Arias 2012, Ledea 2016 and Cruz et al. 2017) and the fundamental uses that are given to plants and species of interest in each region, according to its frequency of appearance and importance of its use in livestock systems (Choque et al. 2018). In this diverse context, the presence of Gliricidia sepium has been reported with very pronounced use in live fences, cutting and carring, and as part of the diet of some ruminants in the Cauto river area. The objective of this study was to determine the chemical composition, in situ effective ruminal degradability (ED) of dry matter (DM) and in vitro apparent and true digestibility of DM, organic matter (OM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) of Gliricidia sepium using the Daysi @ procedure.
Materials and Methods
Experimental procedure. The Gliricidia sepium samples were collected during the rainy season. A total of 10 adult plants were taken at random (5 kg/plant), individual, in a vegetative state, from a vertisol soil of poor drainage (Hernández et al. 1999), belonging to the Estación Experimental de Pastos y Forrajes del Instituto investigaciones Agropecuarias “Jorge Dimitrov” from Granma province, Cuba. In the sampling the browsing of the animal was simulated (Paterson et al.1983). Part of the material harvested, was previously homogenized and dried for 48 hours in a forced air oven at 55ºC.Then ,was milled at 1 mm to determine the chemical composition and in vitro digestibility, and to 2 mm for the in situ ruminal degradability of DM.
The study was conducted in the food analysis and rumen physiology laboratory from the Department of Medicina Veterinaria del Instituto de Ciencias Biomédicas from the Universidad Autónoma de Ciudad Juárez, Chihuahua, México.
Chemical composition. In the analysis of Gliricidia sepium samples, the content of dry matter (DM), ash, organic matter (OM) and crude protein (CP) were determined, according to the techniques described by AOAC (2000). The content of neutral detergent fiber (NDF) and acid detergent fiber (ADF) was estimated by the Goering and van Soest (1970) method by means of a fiber extractor apparatus (Ankom 1998).
In situ ruminal degradability. The degradability of samples was determined by the Dacron bag technique (Ørskov et al. 1980). At each incubation time, the samples were incubated in triplicate in the rumen of two male sheep, with an initial average weight of 40 kg. ± 1.5 and 36 months of age. The animals were provided with a permanent ruminal cannula of 7.5 cm in diameter. They were offered a diet consisting of 70 % alfalfa hay and 30 % commercial balanced food (12 % CP) and were housed in individual metabolic cages with cement floor, sawdust bed and 1.8 m2 surface area. The diets were offered at 8:00 a.m. and 5:00 p.m with free access to a mineral block and water at will. The bags were removed at 0, 6, 12, 24, 48 and 72 h to wash them with water and dried in an oven at 60°C for 24 h.
In vitro digestibility. The technique ANKOM Technology (1998) was used. As donors of ruminal fluid, three Pelibuey male sheep were used, fasting, with 42 ± 3.5 kg of initial average weight and 40 months of age, provided with a permanent ruminal cannula of 7.5 cm in diameter. They were offered a diet related to in situ degradability. For the in vitro test 2 FN°57 bags were used, with pore of 25 μm and dimensions of 5 x 4 cm, of polyester/polyethylene, with filaments extracted in a matrix of three dimensions. The bags were previously identified and washed with acetone. Then, were placed in a forced air oven at 100°C ± 5°C for two hours to dry them and reach constant weight. In each bag 0.25 g of sample were deposited to obtain an effective area of 36 cm2. This corresponded to the relation between the sample size and the bag surface of 14.4 mg/cm2. Subsequently, they were sealed with heat.
Four digestion jars were used, and in each one two repetitions of each forage sample (20 bags/jar) were incubated at random. A bag was included as control (empty and sealed bag without sample) to generate the correction factor for particle entry or weight loss of the bags.
The ruminal inoculum necessary for the procedure (ratio 4: 1 of medium culture solution: ruminal inoculum) was collected by means of a vacuum pump. The ruminal fluid processing of the three donor animals included mixing in a blender for 30 s. It was filtered by double layers of gauze and then (400 mL) was added to the buffer solution (1600 mL/ jar). CO2 was added to maintain the anaerobic conditions present in the rumen. The samples were incubated for 48 h in the Daisy, at 39.2 ± 0.5 °C of temperature, with constant circular agitation. After incubation, the bags were washed with water to stop the fermentation. They were processed in the fiber analyzer. The incubation wastes were in a 100 °C neutral detergent solution for one hour. There were included three successive washes with water at 90 °C and dried in a forced air oven at 105 °C for a minimum of two hours. Subsequently, the bags were weighed to obtain results in terms of in vitro true digestibility of DM (IVTDDM), which are considered as estimates of the actual digestibility of foods.
Data processing and statistical analysis. For ruminal degradability, the results were fitted to the exponential model of Orskov and McDonald (1979):
where:
P |
- Real degradation as a function of time (t) |
a |
- Intersection of the degradation curve at zero time. Represents the component that quickly degrades. |
b |
- Potential degradability of the component |
e |
- Base of natural logarithms (2.71828) |
c |
- Constant degradation rate |
a + b |
- Total degradability of the component |
For the determination of the effective ruminal degradability the Mc Donald (1981) model was applied:
where:
ED |
- in situ effective ruminal degradability |
k |
- Fractional rate of ruminal passage. Different values of k were assumed. |
For the chemical composition, only the standard deviation of the observations with respect to the mean was determined. For the in vitro apparent and true digestibility of the DM, OM, NDF and ADF, analysis of the measures of central tendency and standard deviation was applied.
Results and Discussion
The chemical composition values (table 1) in Gliricidia sepium showed DM content higher than 20 %, while for CP it was 24.79 % DM. The NDF and ADF reached levels of 36.32 and 19.51 % respectively. These results are in the range of values reported by other authors (Pedraza et al. 2002 and Araque et al. 2006) for the studied species, and are much higher than those reported by Ramírez et al. (2010), Fernández et al. (2015) and Ledea (2016) in grasses established under the same experimental conditions. In the values of fibrous indicators, it is shown that this plant can be an option for animal feeding in the studied area, although it has already been reported that Gliricidia sepium (“mataratón”) is always green in the humid and subhumid tropics (Kabaija and Smith, 1989), with a high protein level (Topps, 1992) and high capacity to adapt to different agro-ecological conditions (Escobar et al. 1995). In the studied area, La O et al. (2009) reported a high level of acceptance and use by producers from the Cauto river basin region, so this species is an option for animal feeding, being able to combine with grasses established and studied in this region, with high drought incidence and soil salinity (Ramírez et al. 2010, Fernández et al. 2015 and Ledea 2016)
The ash values 11.41 % were much higher than those reported by Pedraza et al. (2000) and Araque et al. (2006) when studying different cutting ages in an increasing way. These differences in the contents could be related to the degree of adaptation and the responses to the adverse drought conditions and characteristics of the saline soils where this plant is present (La O et al. 2006, 2008 and 2009), as well as to the adaptation of this to different edaphoclimatic conditions in the region, with high vulnerability due to extreme droughts. In this regard it has been shown (Ibáñez 2007) that excessive amounts of salts in the soil can impede the absorption of water by the roots of vegetables and alter the absorption of nutrients. For these reasons, the nutrition of the plants is affected and, in extreme cases, their growth can be inhibited, even talking about toxicity. Therefore, diseases of stem, roots, leaves and seeds occur, due to the bioaccumulation in these organs of certain ions that affect the normal functioning of the plant and cause variability in the ash content.
In addition, under physiological stress conditions, plants are able to create means of defense, such as producing different secondary metabolites and changing some forms of storage and use of chemical components, among which are minerals (Rodríguez 2004). Although this aspect was not studied, for the specific case of these plants, researches are needed to support this hypothesis and its relation with the ecosystem of high drought and soil salinity.
Stewart and Dunsdon (1998) report up to 45 % variation in in vitro digestibility of tropical legumes. According to these authors, a representative percentage is related to the presence of secondary compounds, among which are the tannins. They also state that their positive or negative action is not clear until they have evidence of the specific nutritional effect. However, Pedraza (2000) alludes to the low content of tannins in this plant, an aspect not proven in the plant materials studied in this experiment, which constitutes a question to be defined in subsequent studies.
The estimated values of in vitro apparent digestibility of dry matter and organic matter (IVAPDM and IVAPOM) were lower than the true digestibility (IVTDDM and ITTDOM) in both constituents (table 2 and 3), with contents of apparent and true digestibility, which ranged from 73-77, 64-67, 27-28 and 14-15.00 %, for DM, OM, NDF and ADF, respectively.
Similar tendencies obtained La O et al. (2012) when performed in vitro studies of apparent and true digestibilities, with the use of Daysi in different ecotypes of Tithonia diversifolia, plant also present in these ecosystems and with characteristics of reproduction by cuttings, use in live fences and favorable results as melliferous, in some cases similar to Gliricidia sepium.
Pedraza et al. (2002), when performed in vitro intestinal digestibility studies of Gliricidia sepium with the three steps technique, developed by Calsamiglia and Stern (1995) in protein supplements and modified by La O (2001) for protein plants, obtained values up to 69 % digestibility of non-degraded nitrogen in the rumen. These authors assumed a digestion of 48 h in the rumen and pepsin-pancreatin action for the rest of the degradative process of the bypass protein. However, their results were not conclusive, since in the degradation and nutrient digestion characteristics different factors influence the animal, the diet and the food, those that are wanted to be tested in conjunction with the interactions that take place in the diverse and complex macro and micromolecules present in the food. Although these authors refer that this plant is useful in the productive systems of supplementation.
The effective degradability of DM in the rumen was high, with values higher than 60 %. However, if compared to other shrub plants, it was lower than those reported by La O (2001) for the Leucaena leucocephala cultivars (Peru, 7929, 9379, 9101, 7872 and 7988). These variations can be attributed to the effect of factors such as the species, the cultivar, the management of the plant and the edaphoclimatic conditions.
Table 4 shows the characteristics of the DM degradability. Parameter a was 40.76 % DM, a lower value than those reported by Tolera et al. (1998) in different leucaena species and by Delgado et al. (2001, 2007 and 2008) when working with different tropical trees, in which are L. leucocephala. Something similar happened for c, where lower values were obtained than those found by Kibon and Orskov (1993) when using different shrubs in Nigeria. However, the value of fraction b (36.76 % DM) was lower than those found by Tolera et al. (1998) in L. diversifolia (46.6 % DM), lower in L. leucocephala (50.5 % DM) and higher than those published by Abdulrazak et al. (1996) in L. leucocephala. On this aspect, numerous researchers have showed the great variability in the characteristics of ruminal degradation of nutrients in plants, legumes and tropical trees in general, among which are L. leucocephala (La O 2001 and La O et al. 2006), G .sepium (Pedraza 2000), Tithonia diversifolia, Cordia alba (La O et al. 2008, 2009 and 2012) and trees and shrubs in general (La O et al. 2012 and Domínguez et al. 2012).
When observing the effective DM degradability, the values oscillated between 67-63 % respectively, with variable ruminal turnover rates (k). The results were higher for DM with respect to those obtained by Delgado et al. (2001, 2007 and 2008) in Enterolobium cyclocarpum and other shrubs. They were inferior to those reported by La O (2001) for degradability in L. leucocephala treated with polyethylene glycol (PEG), which is related, in part, to the effect of PEG on polyphenolic compounds.
The evolution of the DM disappearance dynamics after the in situ ruminal incubation (figure 1) showed an increase (P <0.01) in the time until the last incubation time established in this experiment for all the studied components. The results obtained in the degradation were comparable with those reported by Pedraza (2000) with different cutting ages of G. sepium, from other regions very different to those studied in this research.
The kinetic performance was characterized by an increase in the DM disappearance dynamics with the incubation time in the rumen, while the fit of the in situ ruminal degradability data to the proposed model, P = a + b (1 - e- ct), showed R2 higher to 97.00. This shows a correct fit of the degradation values to the model (figure 1).
The results of the analysis of the chemical composition, in situ ruminal degradability of DM and in vitro apparent and true digestibility of the DM, OM, NDF and ADF of Gliricidia sepium show its high nutritional value for the ruminants of the region. However, physiological studies that relates the cut frequency, degree of use of nutrients by the animal and effect of some secondary metabolites on the physiological and productive responses of the animals when intakes the plants in these edaphoclimatic conditions are required.