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In the world, agro-industrial by-products, in general, constitute environmental pollutants (Cegarra et al. 2006). These lignocellulosic residues are mainly composed of cellulose, hemicellolulose and lignin, but they are used in ruminants feeding to replace forage during dry periods, although due to their low nutritional value they must be complemented with other ingredients (Ramírez-Cortina et al. 2012).
The improvement of Cuban livestock could be increased by using the by-products available from the agro-industry, an example of which could be the henequen (Agave fourcroydes) industry and the use of its wastes in animal feeding. This perennial plant is native to Mexico, highly productive in ecological areas limited by the lack of water and soil. It also has high biomass production (± 25 t DM/ha/year), from which the leaves are used, as is the case of pineapple. Their wastes are used as a supplement for cattle, becoming a food that provides high levels of digestible energy, minerals and water (Zamudio, et al.2009).
According to Sánchez and Vásquez (2014), in Cuba, with the defibration of the henequen leaf, only 4 % fiber is used, which generates large volumes of pulp (wet bagasse, juice) with high organic load, obtaining as average 9 t of waste per ton of processed fiber, so that an annual fiber production of 1700 t would generate 15300 t of pollutant, with negative effects for the environment.
The objective of this study was to estimate the kinetics and determine the in situ rumen degradability parameters of the dry matter (ISDDM) of henequen (Agave fourcroydes) bagasse, generated after the industrial defibration of the plant.
The experiment was developed in the Departamento de Manejo y Alimentación de Rumiantes, belonging to the Instituto de Ciencia Animal, located at km 47 ½ of the Central Highway, in San José de las Lajas municipality, Mayabeque province, in the Republic of Cuba.
For the ruminal degradability of the in situ DM, the nylon bag technique was used, described by Ørskov and McDonald (1979), and that of effective degradability, according to McDonald (1981). A fractional rate of passage from the rumen and velocity 2 and 4 % was considered. A total of 24 dacron bags (17 x 4 cm), with porosity of 50 μm and 5 g of ground henequen bagasse (2 mm) were used. The bags were incubated in rumen, in quadruplicate, and in the reverse order of incubation time (72, 48, 24, 12, 4h), to be removed only once and to be able to use the same washing procedure. The zero hour was determined with the same bag number per treatment in a bain Marie with controlled temperature at 39 °C for 15 min.
A cow from Dexter breed, fistulated in rumen, with 350 kg of live weight and housed in an individual cubicle was used, fed with commercial concentrate (6 g kg LW-1) and grass forage and free access to water and mineral salts.
To the samples of henequen bagasse, coming from plants with more than twenty-five years of age, belonging to the Unidad empresarial de base (UEB) henequen "Artemisa", from Ministerio de la Agricultura. The proximal chemical analysis was performed according to AOAC (2005). The protein was determined by the micro-Kjeldhal method, while the metabolizable energy was estimated from the organic matter digestible in the DM, according to CSIRO (1990). All the analyzes were performed in the Laboratorios de Servicios Analíticos del ICA (LASAICA).
The analysis of variance was performed on the degradation results during the incubation kinetics. The Duncan test (1955) was applied to establish differences between means. All the data were processed using the statistical package INFOSTAT (Di Rienzo et al.2012).
Table 1 shows the chemical composition of the bagasse samples, with low values of dry matter, high in energy, organic matter, crude fiber and ash. The latter showed high levels of calcium, poor in phosphorus and relatively low in crude protein. Similar average chemical analysis was reported by Harrison (1984) for henequen bagasse from Mexico and West Africa.
The results of table 2 show differences (P <0.0001) in the in situ degradability of the ISDDM, although with statistical similarity during the last incubation hours (48 h: 63.39 % vs 72h: 63.62 %), moment when it reached the maximum peak of disappearance. The ISDDM value coincides with the one obtained by Harrison (1984), of 64 % for the in vitro degradability of the dry matter, conditioned by the high concentration of carbohydrates in the DM, high solubility (26.6 %) and mineral concentration (151 g kg DM-1) (table 2).
Table 2 Average values of in situ degradation of dry matter (ISDDM) of henequen bagasse
abde different letters in superscripts in the same column indicate significant differences for P < 0.05 (Duncan, 1955) , ± Standard error
Similarly, it could be explained that the increase in the degradation rate of bagasse from the first incubation hours could be determined by the amount of digestible organic matter, variations in the fermentation rate and growth of the microbial population (Godoy 2012). This shows the nutritive value of bagasse, then at 48 h and until the end (72 h) maintains the uniform degradative pattern, being this moment in which the highest digestion of carbohydrates is achieved. After this time, the highly digestible components decrease.
The analysis of regression showed a high degree of fit between the degradability values of henequen bagasse, which affirms the degradative performance of this food and shows that the structural compounds he cell wall did not prevent the action of ruminal cellulolytic microorganisms.
The reached values of potential degradability of DM in this study were superior to those reported by Cáceres et al. (2007) in elephant grass (Cenchrus purpureus), of 56 % and 50 d of age, and those of Madera et al. (2013) also with elephant grass, between 60 and 90 d of age, with 59 % and 52 % of digestibility, respectively. Likewise, they were similar to that referred by Di Marco et al. (2005) with maize silage (61.6 %), and to what Knowles et al. (2008) reported in Cenchrus genus (62.5 %) to 45 d of regrowth.
When considering the cumulative ruminal degradation of the DM, which was 64 %, at 72 h, and the contribution of crude fiber (24 %) of the bagasse, associated with the lignification of the cell wall, as a factor that would cause severe limitations in DM degradation, it could be assumed that 40.4 % of the bagasse would be degraded and absorbed at intestinal level. This could perhaps explain the combined availability of carbohydrates with different ruminal degradation rate in this material during fermentation. This benefit, synchronized with an exogenous contribution of protein in the diet, could favor the synthesis of microbial protein and improve the energy-protein balance. In turn, it would increase the voluntary intake of dry matter by the animal (Fernández 2002).
The obtained results allow intuiting that the ingestion of bagasse by the animals, as well as the amount of energy extracted during the retention of the material in the rumen, could be high (Razz et al. 2004).
Regarding the characterization of the degradability parameters, it was observed that the value of the soluble fraction (a = 28.5 %) made possible the rapid disappearance of the potentially degradable fraction (a+b=64.51 %) and the shorter time of ruminal incubation, which shows the existence of highly fermentable substrate, able to ensure from the beginning the degradative activity of ruminal microorganisms. Although the value of the insoluble fraction, but potential degradable (b=35.96 %) of the DM in rumen contributed with more than half (56 %) of fraction a+ b, at 48 h of incubation, it indicated some protection against the microbial attack in rumen, a situation that favors the pos ruminal use of this material.
Apparently, the value reached in fraction (a) was determined by the high content of soluble carbohydrates in the bagasse, an element that should have influenced on the degradation rate (c = 6% h-1) and by the shorter time of colonization (lag phase = 2.0 % h-1) of ruminal microorganisms (Aragadvay-Yungán et al. 2015).
With respect to the degradation rate (c = 6.7.% h-1), the value reached corresponds to medium quality foods, which require shorter residence time in the rumen for their degradation, and achieve higher deposition of nutrients, to the instead they exceed that of tropical grasses (5.3% h-1). Likewise, this value is similar to that of multipurpose trees (6.2% h-1), as stated by Izaquirre et al. (2011)
Regarding the effective degradation (ED), a parameter that reflects the reduction of potential degradability due to the effect of the passage rate (Araiza-Rosales et al. 2013), associated with the variation in the ruminal turnover rate(k =0.022, 0.004), the values oscillated between 55 and 46 % respectively, which demonstrates the nutritional quality of henequen bagasse.
It is concluded that the variations during incubation kinetics and in situ ruminal degradation parameters of dry matter confirm the possibility of using henequen (Agave fourcroydes) bagasse in ruminant feeding. However, studies on the degradability of the rest of nutrients, characterization of ruminal fermentation and microbial populations are required.
