RESEARCH WORK

Nutritional quality and in situ digestibility of silages from four woody forage plants

María Ligia Roa¹ and J. R. Galeano²

¹Universidad de los Llanos, Escuela de Ciencias Animales km 12 vía a Apiay, Villavicencio, Meta, Colombia
²Grupo de Agroforestería Calle 2A No 33A-25, Villavicencio, Meta, Colombia
E-mail: ligiaroa2607@gmail.com

ABSTRACT

The effect of the conservation time on the nutritional quality and the in situ digestibility of silages from four woody forage plants: Cratylia argentea (T1), Hibiscus rosa-sinensis (T2), Trichanthera gigantea (T3) and Tithonia diversifolia (T4), was evaluated. The plants were pruned after six months of establishment and three months after regrowth, and the leaves and small young branches were used to elaborate 64 silos of 10 kg each, in plastic bags. Each conservation time (0, 30, 60 and 90 days) had four repetitions. To calculate the digestibility of dry matter (DM), total nitrogen (TN), neutral detergent fiber (NDF) and the parameters of effective digestibility (ED), four rumen-fistulated cattle were used, distributed in a 4 x 4 Latin square. The silages showed nice aspect and color, with pH between 4,2 and 4,6 and ammoniacal nitrogen lower than 1 %. The TN percentage was higher (p> 0,05) for T1 (2,52) and T2 (2,43), and this nutrient was reduced until 90 days. The ED of the DM, TN and NDF was higher (p> 0,05) in T2, with a trend to decrease with the conservation time (90 days). This same performance was shown by fractions A, B and c. The highest lignin content appeared in T3 (5,45 %) and T4 (5,60 %), indicator that affected negatively the rumen kinetics. The decrease of the nutritional quality and digestibility due to the conservation time was lower for T2 and T3. It is concluded that the organoleptic properties of the silages were optimum, the ammoniacal nitrogen did not exceed 1 % and the lactic acid varied between 1,0 and 3,6 %; while time affected to a lower extent the nutritional composition of the silage of H. rosa-sinensis, with regards to the other forage plants. It is recommended to ensile for the dry season and use the silages before 60 days of conservation.

Keywords: Cratylia argentea, Hibiscus rosa-sinensis, Tithonia diversifolia, Trichanthera gigantea, nutritional value.

The piedmont plain (Colombia) is a zone of the humid tropic, with a dry season of four months, in which pasture and forage availability and quality are negatively affected, situation which reduces the reproductive and productive capacity of cattle. That is why the use of supplements is recommended, in order to prevent, through an adequate supply of energy and protein nutrients, losses in the body condition of the animals, and in extreme cases, death (Plazas, 2010).

Taking into consideration that concentrate protein sources are costly, work has been done on the search for alternatives that are economical and viable, such as silages, because when protein is contributed in inadequate quantities cattle production is disfavored (Amata and Lebari, 2011).

In silages, it is important to maintain the anaerobic conditions to increase the population of lactic bacteria, which are in charge of fermenting the sugars present in forages and guaranteeing the acid environment that is required for a good conservation, while other aspects, such as the conservation time, the harvest age and the microbiological quality, are taken into consideration to elaborate a good product and maintain the nutritional properties of the original forage (Reyes et al., 2009). Silage fermentation can be monitored through indicators which establish that the process was adequately developed (Villaba et al., 2011); they can be biological, physical and chemical. Among the last ones are the dry matter contents, soluble carbohydrates, protein, ethereal extract and reducer sugars (Dormond et al., 2011).

On the other hand, the animal production systems which include trees and shrubs turn out to be better than the ones based on grasses, because their foliage provides higher protein content as compared with that of most pastures. Such plants can be cultivated by farmers in large or small farms (Miranda et al., 2015).

In that sense, for the Piedmont zone the introduction of trees and shrubs which have shown good adaptation (Plazas, 2010), such as Cratylia argentea, Hibiscus rosa-sinensis, Trichanthera gigantea and Tithonia diversifolia, has been proposed as a sustainable solution.

In double-purpose cows that grazed Brachiaria decumbens, the inclusion of fresh or ensiled C. argentea, as a supplement, increased milk production. This species is considered an advantageous option for small farmers, because it allows them to decrease the use of concentrate feeds and reduce up to 7 % of the production costs (Rosero and Posada, 2007).

On the other hand, the inclusion of H. rosa-sinensis hay in a diet for sheep based on Cynodon nlemfuensis increased the nitrogen contribution and induced linear increases (p< 0,05) in the digestibility of dry matter, organic matter, protein and neutral detergent fiber (Ruiz et al., 2006).

T. gigantea produces annually up to 60 t of fresh forage/ha and its use is recommended in ruminants. Nevertheless, the hypothesis that its foliage shows limiting factors regarding the digestibility and the balance of essential aminoacids, leading to a reduction of its intake, has been stated (Araque et al., 2005).

T. diversifolia is a species reported as promising for the nutrition of ruminants, sheep, pigs and rabbits in the zone; however, its potential as ensiled forage has not been proven (Nieves et al., 2011; Gallego-Castro et al., 2014).

Taking such antecedents into consideration, the objective of this study was to evaluate the effect of the conservation time on the nutritional quality and in situ digestibility of these four forage woody plants.

MATERIALS AND METHODS

The study was conducted at the University of the Llanos, located at km 12 Puerto López road in the Vereda Barcelona, with an altitude of 465 m.a.s.l., temperature of 27 ºC and annual rainfall between 1 900 and 3 250 mm.

The plants used were: C. argentea, H. rosa-sinensis, T. gigantea and T. diversifolia, which were planted and left to grow for six months and afterwards their crowns were pruned. Three months after regrowth, a cut was performed on the leaves and small young branches. The plant material was chopped to a size of 2 cm and placed in caliber No. 4 plastic bags.

Tamping was manually performed, and after completely withdrawing the air from them, the bags were sealed with Scotch tape. The storage place was located in a dry and covered site.

The treatments consisted in the silages of C. argentea (T1), H. rosa-sinensis (T2), T. gigantea (T3) and T. diversifolia (T4), with four repetitions for each conservation time (0, 30, 60 and 90 days), for a total of 64 silos of 10 kg each.

Samples were taken from each repetition and organoleptic observations were made before taking them to the laboratory of animal nutrition, where the following parameters were determined: pH, ammoniacal nitrogen, dry matter (DM), total nitrogen (TN), neutral detergent fiber (NDF) and lignin (AOAC, 2005).

For the determination of the in situ digestibility four cattle (Criollo x Zebu), fistulated in the rumen, with an average weight of 370 ± 20,5 kg, were used. They were distributed in a simple crossover design (table 1), and the four experimental periods were considered replications.

The animals remained continuously grazing B. decumbens and had salt and water ad libitum. They were supplied 5 kg of silage per day, with an adaptation period of ten days and four days of data collection, covering an experimental period of 14 days. The silages were incubated in the rumen of the animal corresponding to each treatment and conservation time, and the dry matter (DMD), total nitrogen (TND) and neutral detergent fiber digestibility (NDFD) was analyzed, with incubations in the rumen at 0, 12, 24, 48 and 72 h.

To determine the DMD and describe the degradation kinetics, the in situ method proposed by Ørskov (2002) and Mertens (2002) was used.

The statistical model was the following:

Yijk = µ + ti + fj + ck + eijk

Where:

Yijk: Reading of the i-eth treatment; where: i: silages; j: periods 1, 2, 3, 4; k-eth column: fistulated animal 1, 2, 3, 4.

µ: general mean.

ti: effect of treatment i, with i = 1, 2, 3, 4.

fj: effect of period j, with j = 1, 2, 3, 4.

ck: effect of the fistulated animal k, with k = 1, 2, 3, 4.

µijk: error associated with the reading of the i-eth treatment in the j-eth period and in the k-eth fistulated animal.

The results were analyzed applying Tukey's test, through the statistical program SPSS 15 (Pérez, 2009).

The effective ruminal digestibility (ED) of DM, TN and ND of the four silages was also evaluated. For such purpose the mathematical model of ruminal kinetics (Mertens, 2002) was used.

Y = A + B (1-E^c*t)

Y (ED) represents the effective digestibility in percentage of disappearance of the degraded material and A, B and c are the parameters to be estimated.

t: incubation time.

A: intercept with axis «Y», it establishes the rapidly degradable soluble substratum (to determine this fraction the samples were incubated within the nylon bags in ruminal liquid during 40 minutes in bain-marie at 39 ºC, before being filtered and dried).

B: fraction degraded at 72 hours.

c: fractional rate of rumen passage, percentage/hour.

k: the constant 0,044 suggested by Ørskov (2002) was used.

E: exponential of c*t.

RESULTS

The silages showed excellent organoleptic conditions in the four fermentation periods: ripe fruit scent, olive green color and texture of continuous contours, besides being totally consumed. The pH was in a range from 4,2 to 4,6 and the ammoniacal nitrogen was lower than or equal to 1 % (table 2).

The highest DM content (p< 0,05) was found in the C. argentea silages (table 2). The TN percentage in all the conservation times was higher (p< 0,05) for silages T3 and T4; as the conservation time advanced, the TN decreased in 30 % for T3 and in 20 % for T4. Similar performances were observed in the other treatments. The highest percentage of NDF was found for T1 and T4 (p< 0,05), with increases of 11,2 and 21,1 percentage units at 90 days, compared with the initial values before conservation. An increase of DM, NDF and lignin was observed at 90 days in the four species, compared with time zero; while the highest total nitrogen percentage was for T2 (p< 0,05), although this indicator decreased with the conservation time.

Similar results were found in the effective digestibility (ED) of DM. At 90 days the decrease was 18,8; 20,3; 23,3 and 19,4 percentage units for T1, T2, T3 and T4, respectively (table 3). The average decrease of ED due to the effect of the conservation time was 6,8 %, while in fractions «A», «B» and «c», as average of the four treatments, it was 9,92; 22,63 and 19,79 %, respectively. T4 showed the lowest values in all the conservation periods.

The ED and soluble fraction A of DM were higher (p< 0,05) for T2 and T3, and although fraction B was similar for all the treatments, the percentage had a trend to decrease (figs. 1 and 2). Equal performance was observed in fraction c.

Fractions «A», «B» and ED of NDF were higher (p< 0,05) for T2 and T3 compared with the other two treatments (table 4), while fraction «B» was similar for all the silages, with the exception of T4 (p< 0,05).

The ED of the NDF was lower (p< 0,05) in T3. In all the treatments this variable was reduced between 5,0 and 8,5 % at 90 days (figs. 3 and 4).

The ED of the ruminal kinetics of TN in the four treatments decreased (p< 0,05) at 90 days in 21,17 (T1); 19,84 (T2); 19,6 (T3) and 18,0 (T4) percentage units, respectively (table 5), with the highest ones (p< 0,05) at all conservation times for T2 and T4. It is important to state that as the fermentation time increased, the ED decreased. T4 was lower (p< 0,05) in the values of fractions A, B and c with regards to the other treatments.

DISCUSSION

The fermentation time of the silages affected the DM, NDF, TN and lignin contents. In the case of DM, it increased with the conservation time in more than 10 percentage units at 60 days in all the forage plants, a performance similar to the one obtained by Viengsakoun et al. (2015) in silages elaborated with cassava residues. This DM increase (from 17,50 to 30,95 % at 60 days) may be due to the fact that the water of the forage reacts with the soluble components, which are transformed into volatile fatty acids: acetic, butyric and lactic acid. On the other hand, there was an increase of the NDF and lignin values with the conservation time; this caused the cell content, in which soluble nitrogen is lodged, which is in turn part of TN, decreased with time.

To establish the proportion of nutritional fractions which are degraded or not in the rumen, it is necessary to estimate the effective digestibility (ED). The forages are constituted by three fractions: the rapidly-degraded fraction, the slowly-degraded fraction and the indigestible fraction. The first one includes sugars and some soluble nitrogen compounds which disappear in the first six hours; while the second includes the components of the NDF, cellulose and hemicellulose, which are degraded until 72 hours and their values depend on the type of forage and its maturity status (Rosero et al., 2010).

The ED of the NDF was higher in T2 and T3, which indicates that the cell content was available for the rumen bacteria; this allowed to increase their population and, thus, their efficiency in the degradation of other nutrients (Correa, 2008). In addition, when the protein is degraded in the rumen ammonia is released, which is a weak base and can react with the cell walls (NDF) or with their fermentation products, volatile fatty acids, forming the bacterial protein.

These results are similar to the ones found by Kyaw San et al. (2015), who fed fistulated cattle with corn silage, and observed a quadratic effect (p< 0,01) on the total digestibility of NDF and ADF as the conservation time increased.

In ruminant nutrition, the TN content of forages and its performance in ruminal kinetics are important indicators (Valencia, 2010). Such premises were fulfilled for T4 and T3, because these silages were the least affected in the TN content during the conservation process, with decrease at 90 days of 20 and 30 % vs. 42,2 and 37,1 % for T1 and T2, respectively. However, in T2 the variables of the fermentation kinetics in the rumen (ED and c) were higher than those of T1 and T4 during all the conservation times, which allows to infer that the quality of the cell wall is determining in the TN availability in the rumen.

Mahecha and Rosales (2005) reported, for the fraction B of the DM of T. gigantea and T. diversifolia silages at zero days of conservation, higher values (74,0 and 90,0 %) than the ones in this study. This difference could be associated to different values in the chemical components of the forages, which are related to their morphological traits, but also to the soil and climate where they grow.

The proportion of structural carbohydrates in each silage was different. The NDF and lignin, which represent the cell wall, were lower in T2 and T3, indicating that there was a higher quantity of soluble compounds available for the animal, compared with T1 and T4 (Palma, 2005). This availability allows such silages to have a more efficient synthesis process, showing higher degradation by ruminal bacteria.

The ruminal fermentation kinetics depends on two critical aspects: the speed to start degradation and the passage rate «c». The combination of these two aspects establishes the net quantity of microorganisms that synthesize the nutrients and which are later utilized and digested in the abomasum and the intestine (Sosa et al., 2004).

The results confirm the superiority of the effective digestibility of DM and NDF and of fractions B and c of the H. rosa-sinensis (T2) and T. gigantea (T3) silages, which was shown in the TN available in the rumen, because their high ED and passage rate c can be negatively affected when microorganisms take long to fractionate the cell wall to make available its content, which is constituted by soluble nutrients such as TN (Rodríguez and González, 2006).

C. argentea and T. diversifolia showed a higher content of lignin, compound that negatively intervenes in the fractions of the ruminal kinetics due to associations in its chemical composition, which causes negative effects on nutrient availability.

It is concluded that, from the organoleptic point of view, the silages had optimum quality, while the ammoniacal nitrogen did not exceed 1 % and lactic acid varied between 1,0 and 3,6 %.

When increasing the conservation time of the silages, the DM (12,8 %) and lignin contents (2,3 %) also increased, while the TN content showed a trend to decrease (0,43 %), with a more critical reduction in T. diversifolia.

The parameters of ruminal kinetics, such as ED and fractions B and c in the DM, TN and NDF, were higher in H. rosa-sinensis and T. gigantea, while the conservation time affected to a lower extent the nutritional composition of the H. rosa-sinensis silage, with regards to the other woody forage plants.

It is recommended to ensile these forages as feeding alternative for the feed scarcity season, although it should be taken into consideration that the initial nutritional quality of the forage decreases after 60 days of conservation. It is necessary to continue studying in order to find conservation strategies in which the nutritional quality and utilization of the silages are not affected.

Received: May 27, 2015
Accepted: October 12, 2015