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Introduction
The production of grasses and forages in ruminant’s production systems, in most of the tropics, contribute 80 to 90 % of the nutrients required by the animals. They are the most economical option for bovine feeding and do not directly compete with the man diet, since they are generally used to promote lands that are not very productive or not suitable for other crops. Although the positive effect of the introduction of these improved grasses on the productivity of livestock systems is known, efforts have not always meant an increase in animal production or the expected results, due to the negative influence of factors such as: adaptation of species to environmental conditions, access to fertilizers and other inputs for their maintenance, management and care of the environment with good practices, as well as the cost- production relation (Cruz et al. 2015).
The development of meadows improvement techniques in tropical regions still faces the difficulties of establishing and exploiting them. The ultimate goal of establishing grasses is to improve the animal production system. To implant a grass in a livestock entity is to incorporate a valuable forage resource. However, its entry into the production system involves considerable financial effort in its implementation, making expenditures for soil tillage, fertilization and seed purchase, among other aspects (Espínola and Paniagua 2010).
In general, the cultivated grass produces more quantity and better forage quality than the natural meadow, it would allow for higher stocking rate and better productivity in meat and milk per unit area. The production of Brachiaria can oscillate between 8 and 10 t DM/ha/year, depending on the soil fertility and the precipitations that modify this potential, its adaptation and persistence. These aspects may represent a limitation for bovine production because of its effect on productivity despite the characteristics and versatility of these species (Fernández et al. 2015 and Roja-García et al. 2018).
On the other hand, Cruz et al. (2017) obtained average values of crude protein of 10 %, oscillating between 8 and 13 % in hybrid Brachiaria cv. Mulato 1 and the average digestibility of the forage produced by this species was 66 %, with a range that can vary between 56 and 75 %, depending on the regrowth age. In hybrid Brachiaria BR02/1794 Roja-García et al. (2018) reported an average decrease of CP with the age of 20 to 7 % for leaves and 13 to 4 % for stems, while the cell wall increased from 56 to 68 % and from 68 to 72 % for these fractions, respectively.
Ecuador has varieties of Brachiaria in which no extensive studies have been conducted, so it is necessary to know their productive performance and their nutritional contribution. That is why the objective of this study was to evaluate some indicators of the performance and bromatological composition of three Brachiaria varieties in El Empalme area, Ecuador.
Materials and Methods
Location. This research was carried out at the Orlando Varela farm, located at kilometer one of the El Empalme-Balzar road, left margin, democracy sector, El Empalme canton, Guayas province, Ecuador. It is located between the geographical coordinates 01° 06' of south latitude and 79° 29 of west longitude at a height of 73 m o.s.l. The experiment was carried out between July and September 2015, considered as a dry period.
Agrometeorological conditions. The climate of the territory is classified as humid subtropical, with average rainfalls of 2229.60 mm/year. The average temperature is 25.80°C; relative humidity 86 %, Inceptisol soil (Soil Survey Staff 2003) and its chemical composition is in table 1.
Treatment and experimental design. A randomized block design with factorial arrangement (3x3) was used: three varieties (Brachiaria decumbens, Brachiaria brizantha and hybrid Brachiaria Mulato l) and three regrowth ages (21, 42 and 63 days) and five replications.
Procedure. The experimental plots (5x5 = 25 m2) were sowing in February 2015 at a distance of 50 cm between rows and 20 cm between plants. The plants had a period of establishment until July, where the uniformity cut was made. From there, samplings at 21, 42 and 63 days of regrowth were made, eliminating 50 cm of border effect and cutting all the material from the harvestable area at 10 cm above soil level. The biomass production, yield of total dry matter, of leaves and stems, number of leaves and stems (by bunch); as well as the length and width of leaves, and the leaf-stem ratio were evaluated (Forte et al. 2016). Then two kilograms were taken for each of the treatments (five samplings/age) for further analysis in the laboratory.
Only irrigation was used to facilitate germination and establishment, and no fertilization or chemical treatment was used to eliminate weeds. At the beginning of the experiment, the population of the varieties in the plots was 99 %.
Determination of chemical composition. The DM, CP, ash, OM, P and Ca were determined according to AOAC (2000); NDF, ADF, ADL, cellulose (Cel), hemicellulose (Hcel) and cellular content (CC) according to Goering and Van Soest (1970); the digestibility of dry matter was quantified by Aumont et al. (1995) and the metabolizable energy and net lactation energy were established according to Cáceres and González (2000). All analyzes were performed in duplicate and by replication. In addition, the NDF/N and DDF/A relations were calculated.
Statistical analysis and calculations. Analysis of variance was performed according to the experimental design and mean values were compared using Duncan’s (1955) multiple range test. For the normal distribution of the data the Kolmogorov-Smirnov (Massey 1951) test was used and for the variances the Bartlett (1937) test.
Results
For all the studied indicators, there was interaction (P <0.0001) variety x regrowth age.
The highest yield of total DM, of leaves and stems (2.49, 1.37 and 1.12 t/ha, respectively), as well as for biomass (8.64 t/ha) was obtained with the Mulato 1 variety at 63 days of regrowth and all the varieties increased this indicator with their maturity (table 2).
Table 2 Yields of three Brachiaria varieties
abcdefg Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
For the morphological indicators (table 3) the best results in height, number of leaves, leaves length and leaves width were obtained in Mulato 1 variety at 63 days of regrowth with 1.07 m; 952; 0.40 m and 0.021 m, respectively. While the highest number of stems was for B. decumbens with 160 at 63 days of regrowth.
Table 3 Morphological indicators of three Brachiaria varieties
abcdefgh Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
The highest percentages of CP and cellular content (CC) were recorded at 21 days of regrowth in Mulato 1 and B. brizantha (14.23 % and 74.77 %, respectively), while the highest values for fibrous components (NDF, ADF and Cel) were obtained in Decumbens variety at 63 days of regrowth (47.24, 27.35 and 23.20 %, respectively). B. brizantha excelled in the content of LAD and hemicellulose (5.44 and 20.10 %) at 63 days of regrowth (table 4).
Table 4 CP content and fibrous fractionation of three Brachiaria varieties
abcdefgh Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
The highest percentages of ash and P (14.87 and 0.025%, respectively) were obtained in B. decumbens at 63 days; those of Ca (0.68 %) corresponded to B. brizantha with 63 days of regrowth and the OM (91.13%) was recorded in Mulato 1 at 21 days of regrowth, respectively (table 5).
Table 5 Values of minerals and organic matter of three Brachiaria varieties
abcdefgh Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
Table 6 shows that the best leaf/stem ratio was showed by Mulato 1 (2.83) at 21 days of regrowth, while B. decumbens at that same age recorded the highest NDF/N and ADF/N relations (35.41 and 20.50, respectively). The B. brizantha and Mulato 1 at 21 days of regrowth and without differing among them showed the highest values of DMD, OMD, ME and FNE (59.37 %, 60.51 %, 8.80 MJ/kg and 5.14 MJ / kg as mean values, respectively).
Table 6 Some quality indicators of the three Brachiaria varieties
abcdefgh Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
Discussion
The age and cutting height are the main components in the management of forages that influence on the yield. Cruz et al. (2017) when studying the Brachiaria humidicola, with 21 and 28 days of cutting frequencies, in Tabasco, Mexico, they found total yield, of leaves and stems of 0.34; 1.42 and 0.88 tDM/ ha, for the dry season with 42 and 9 % less of production than rain and every 28 d. On the other hand, Roja-García et al. (2018) in hybrid Brachiaria BR02/1794 when studying frequencies between 7 to 63 d and cutting heights of 10 and 15 cm found higher yields in the second height, concluding that this performance is due to the fact that there is a higher remaining leaf area which causes the biomass recovers more easily, maintains higher reserves of carbohydrates, increases the persistence of the meadow and prevents soil erosion (Ramírez et al. 2010).
Espínola and Paniagua (2010) and Cruz et al. (2017), when evaluating biomass production in B. brizantha, found yields of 13.50-13.82 t DM/ ha, while Atencio et al. (2014), reported 4-10 tDM /ha when studying 14 varieties of Brachiaria with three moisture levels reported the best performances for BR02/1752 and CIAT16051. Results superior to those of this research, but under different edaphoclimatic conditions could influence. In this sense Cruz-Hernández et al. (2017) stated that at lower cutting heights, yields are affected and that Mulato grass with heights of 13-15 cm shows a higher population of stems. The biomass accumulation of forages can be attributed also to the increase in the stems density, in the individual weight of each stem or a combination of both, this is because the stem is considered as the primary growth unit and the meadow can be considered as a population of these, aspect that should be considered in the differences in this study and those previously reported.
The changes in the morphological composition are conditioned by the edaphic and climatic conditions, which can increase or decrease the growth of leaves and stems, as well as vary their proportions. Ortega-Aguirre et al. (2014) and Cruz-Hernández et al. (2017) found that the leaves increase their appearance, when there is temperature between 20 to 32.5 °C, but decrease if the temperature exceeds 35 °C. With respect to the dry season, the changes could be due to the fact that the growth of the plants was inhibited by the low temperatures, while the hydric stress allowed low growth. They affirm that the plant age determines the distribution of dry matter in the morphological components. The proportion of leaves in the harvested forage decreases as the interval between harvests increases, due to the higher growth of the stem, when the environmental conditions are favorable for the plants growth as it happens in the rainy season.
Hence, the management of the defoliation of a meadow influences on the growth rate, production, botanical composition, quality and its persistence (Nantes et al.2013). This indicates that it is important to consider not only the forage yield, but also the proportion of leaves in relation to the stems. This could contribute to explain the performance of the morphological indicators studied.
For the chemical composition there was interaction variety x regrowth age. However, in all varieties the DM, NDF, ADF, ADL, Cel and Hcel were increased, while CP and CC decreased with the regrowth age. This process is due to the fact that, depending on the type of tissue, as the plant cell matures, the cell wall widens and commonly produces a secondary wall of different composition, which is why chemical and anatomical changes that affect the digestibility occur. This was related to the fact that at younger ages there is higher succulence of leaves and more young stems (Ortega-Aguirre et al. 2014 and Roja-García et al. 2018).
In this regard, Barrera-Álvarez et al. (2015) and Fortes et al. (2016) stated that age affects the chemical composition of grasses, the variability between cultivars of the same species are usually small, although they can also influence on the availability of water, soil and their fertility, and season of year, among others. However, the values of the components of the cell wall, CP and CC are within the range reported by the specialized literature.
López et al. (2017) and Reyes-Pérez et al. (2018) reported a similar performance in Brachiaria brizantha and Andropogon gayanus and related this performance with the physiological and anatomical changes that occur as the plant ages, which causes the decrease in the proportion of the cytoplasmic cellular content; the cellular lumen is reduced with its soluble components and the fibrous components are increased. This is further accentuated by increasing yield, due to the water balance of the plant and the amount of nitrogen available in the soil. In addition, the percentage of stems, senescent leaves and the lignin content is higher.
For the content of minerals and organic matter despite the interaction found, there was little variability between the attributable varieties according to Balseca et al. (2015) to the effect of climate factors specifically rainfalls and temperatures, which lead to the minerals necessary for the plants growth are in the dissolution of the soil and the roots have relative ease for absorption, response pattern which was confirmed by Jarma et al. (2012) in Brachiaria humidicola and Merlo-Maydana et al. (2017) in Brachiaria brizantha. However, Valbuena et al. (2016) and López et al. (2017) in Brachiaria brizantha and Patiño et al. (2018) in Megathyrsus maximus found that ash tends to decay with increasing age, because plants require different amounts of minerals depending on their phenological state.
In terms of quality indicators, the interactions found is an indication that these factors should be evaluated as a system and not in isolation, they are usually influenced by climate, soil, fertility and management, among other aspects. These species of introduced grasses have as main characteristics to improve their productivity and nutritional value. Therefore, it is of interest that during the study favorable amounts of leaves have been obtained with respect to the stems (leaf/stem ratio) with productivity of more than 50 % for this first fraction. However, it maintains the same response that is reported in the literature for tropical grasses with increase of the NDF/N and ADF/N relations, as well as decrease of energy supply (ME, FNE) and digestibility (DMD, OMD) ( Cruz et al. 2017).
In Brachiaria humidicola, B. decumbens and B. brizanthaEspínola and Paniagua (2010) reported leaf/ stems ratios at 60 days of 0.85; 2.24 and 7.34, respectively, which reaffirms the ability of these species to produce more leaves with respect to the stems. The quality of tropical forages is affected by the maturity with better distribution of nutrients during the first weeks of regrowth, especially nitrogen and increase of the fibrous fraction with age. This can be attributed to the higher proportion of leaves and the appearance of tillers, as well as to the plant’s need to create the necessary substances for its development (Ortega-Aguirre et al. 2015).
The decrease of the digestibility of the dry and organic matter with the increase of the age could be influenced by the plant growth (maturity), which brings a thickening of the cell wall, fundamentally of the primary wall, which reduces the intercellular space where nutrients (protein) are, and is in function of the relative proportion of each chemical component and its individual digestibility. On the other hand, it is also influenced by the increase of the structural components, as well as the silica and monomeric components of lignin. Results superior to 50 % of digestibility for these species were obtained by Barrera-Álvarez et al. (2015) and Mojica-Rodríguez et al. (2017). While Cruz et al. (2017) in Brachiaria humidicola vc. Chetumal with cutting frequencies every 21 and 28 days found results of 54-60 %, values below those reached in this study. The differences of intra- and inter-species degradability may be associated with the characteristics of each species and genus. In addition, the relation between chemical indicators and ruminal degradability must be present not as a sum of factors but as the joint influence of chemical components as a system on degradability (Avellaneda et al. 2015).
The decrease of metabolizable energy and net lactation energy with the age according to Cruz et al. (2017) is due to chemical and biochemical transformations in the plant components such as the reduction of soluble carbohydrate values, digestible proteins and dry matter digestibility. In addition, it should be added that the energy value of forages depends on the organic matter digestibility, which is closely related to the composition of the plant (Balseca et al. 2015).
Two constituent groups are known in plants, those of cellular content and wall. The first ones are formed by sugars, organic acids, nitrogenous substances and lipids, whose actual digestibility in ruminants is total (carbohydrates) or almost total (proteins and lipids). The second ones, which include polysaccharides, cellulose, hemicellulose and pectic substances that have a very variable digestibility (40-90 %), and lignin, which is considered totally indigestible. All these elements increase as the plant ages, reducing the digestibility of dry matter and organic matter, resulting in a decrease in energy (Combatt et al. 2015).
Conclusions
There was variability in terms of the varieties in the studied indicators, with the best performance for Mulato 1. However, it was demonstrated that as the maturity of the plant advanced, there was a decrease in its nutritional quality determined, among other aspects, by the lower digestibilities and energy, as well as increases in the FDN/N, FDA/N relation but, it is necessary to emphasize that although the leaf/stem ratio decreased with age, the leaf production in all the studied cultivars was above 50 % with respect to the stems, aspects to be taken into account in the management of these plants in the ruminants production systems.
