Use of “dry ammoniation” to improve the nutritive value of Brachiaria humidicola hay

A Barrios-Urdaneta   and   M Ventura

Dpto. de Zootecnia. Facultad de Agronomía,
Universidad del Zulia, Maracaibo, Venezuela
abarrios2@cantv.net   mxv@icnet.com.ve

Abstract

The “dry ammoniation” method was developed at “La Esperanza” farm, University of Zulia, Venezuela, located in a dry tropical area, as a means to improve the quality of tropical hays without the humidity problems observed with  the wet technique.

The effects of storage time (14 and 21 days), water volume (200 and 400 ml/kg hay) and urea quantity (20 and 40 g/kg hay) on the crude protein content (CP) and in vitro digestibility of NDF were studied using a factorial arrangement design (2x2x2) plus one control (non-treated hay) with three replications per treatment. Small hay bales of 1 kg, made from several commercial hay bales of Brachiaria humidicola, were used as experimental units. The urea solutions were added into plastic containers (19 l) before placing the hay, leaving a space of 5-8 cm between the hay and the solution. Thereafter the containers were covered hermetically with a plastic sheet and stored under a roofed area.

The “dry ammoniation” improved the CP (3.2 to 8.3%) as well as the NDF in vitro digestibility (46.2 to 57.1%), when the control hay was compared against the average of the treated hays. The best result was obtained when the hay was stored for 21 days and treated with 200 ml of water + 40 g of urea/kg (10.6 % CP and 63.1% NDF in vitro digestibility).

Key words: Ammoniation, dry treatment, Brachiaria humidicola, hay, nutritive value.

Introduction

The low nutritive value of tropical grass hays is mainly responsible for the low productivity observed in many animal production systems in the tropics. The low protein content and the high degree of lignification are two major factors influencing utilization by ruminants. There are different physical, biological and chemical techniques that can counteract the negative effect of these factors. Ammoniation is one of the chemical treatments most studied in the past few years. This technique is based on the hydrolytic action of the ammonia over the linkage between the lignin and the structural polysaccharides, thus increasing the organic matter potentially available for the ruminal microorganisms. This treatment also improves the crude protein content through a fixation process of part of the ammonia. Such changes interact promoting a better rate of digestion (Sundstol et al 1978).

Gaseous anhydrous ammonia has been used in developed countries, while in tropical regions of the developing countries the spraying and dipping of hay in urea solutions has been preferred (Chenost and Kayouli 1997).  The first method is more effective, but its high cost and the special storage facilities required have made it difficult to be adopted by farmers. The use of a urea solution is a simple and low cost technique; however, it has not become yet an alternative widely accepted. The labor involved to handle the material and the appearance of molds as a consequence of the high humidity have been some of the limiting factors to allow acceptance by the producers at the commercial level. All these limitations prompted us to improve the procedure and thus the so called “dry ammoniation” technique was developed at “La Esperanza Farm” in the University of Zulia in Venezuela. This technique combines the basic characteristics of each of the two techniques discussed above, since it uses gaseous ammonia released from urea with no wetting of the hay required, thus avoiding the handling and molding problems (Barrios y Ventura 2001a).

Even though the preliminary results observed using this technology were positive, it is important to study different factors that could affect treatment efficiency so that a reliable and precise technology could be offered to our farmers.

Materials and Methods

This study was conducted at “La Esperanza Farm” of the University of Zulia, located in a dry tropical region (10° North latitude and 72° 40´ East longitude). Small hay bales (1 kg), made from material taken from commercial bales of Brachiaria humidicola, were used as experimental units. The effects of storage time (14 and 21 days), water volume (200 and 400 ml/kg of hay) and urea quantity (20 and 40 g/kg of hay) on the crude protein (CP) and neutral detergent fiber in vitro digestibility were studied. A factorial arrangement ([2x2x2] + control [non-treated hay]) with three replications per treatment was used. The treatment effect was analyzed through the orthogonal contrast, using the GLM  procedure (SAS 1988).

Each experimental unit was prepared as follows: the corresponding urea solution was added first to a 19 litre plastic cylindrical container, placing simultaneously a small amount of hay as an ureolitic agent. Then the small bales were placed in the container, leaving a clear space of 5 to 8 cm between the urea solution level and the hay, to avoid wetting of the material. Finally the top of the container was covered with plastic to avoid loss of ammonia and then stored for 2 or 3 weeks according to the  assigned treatment.  When the storage time was over, each container was uncovered and the hay was removed and exposed to the air for 3 h. A sample was taken from each bale to determine N (AOAC 1990) and NDF in vitro digestibility using the modified Tilley and Terry method (NDF solution instead of pepsin [Van Soest 1967]).

Results and discussion

The “dry ammoniation” improved (p < 0.001) the nutritive value of the Brachiaria humidicola hay (Figures 1 and  2). These results are in agreement with findings reported by several authors, using different techniques as well as different fibrous materials (Silva and Ørskov 1988; Fondevila et al 1994). The changes observed in the proportional increment of the crude protein and NDF in vitro digestibility are very similar to those reported by Klee and Murillo (1989). They found increments of 178 to 240 % in crude protein and between 33 and 39 % in the dry matter in vitro digestibility when wheat straw was treated with different levels of anhydrous ammonia.

The amount of urea used had a significant effect on both the crude protein content and digestibility. The crude protein value obtained with the use of 40 g urea/kg hay was higher (p < 0.001) than with 20 and 0 g urea/kg hay (10.1, 6.5 and 3.4 %, respectively; Figure 1). Brown and Adjei (1995) found similar results when Panicum maximum hay was wet-treated with urea solutions equivalent to 0, 40, 60 and 80 g urea/kg. The final crude protein values reported were 4.3, 10.5, 13.8 and 18.4 %, respectively. Preliminary observations showed  increments in CP inferior to one percentage unit when urea was used at levels above 40 g/kg using the “Dry ammoniation” technique on Brachiaria humidicola hays (Barrios and Ventura 2001b). It must be emphasized that the wet or spraying technique using urea solution results in higher crude protein values in the treated fibrous material, due to a greater impregnation of the plant tissue. The in vitro  NDF digestibility was affected in a similar way to the crude protein  when the amount of urea was increased (Figure 2).

Figure 1: Effect of concentration of urea on crude protein content of the hay

Figure 2: Effect of concentration of urea on NDF in vitro digestibility of the hay

 

The water volume used affected (p< 0001) the crude protein content, with observed  values of 9.3 and 7.3 % in DM when 200 and 400 ml /kg hay were used, respectively (Table 1).  The higher crude protein values were associated with a higher concentration of urea in the 200 ml/kg level. Probably there was a lower amount of NH3  given off due to a larger enzyme dilution at the 400 ml level. On the other hand, the NDF digestibility was not affected (Table 2).

The moisture content of the hay increased from 12 % to about 18 %, as a result of the evaporation and condensation of the urea solution. This moisture content is low when it is compared to the wet and spraying techniques and therefore it could make the difference as far as the mold appearance in high humidity conditions. According to Sundstol (1988) the humidity in the fibrous material favors the treatment action, but levels above 15 to 20 % moisture can cause problems in the alkali distribution and the mold contamination.

The storage time affected considerably the NDF in vitro digestibility (Table 2), being higher (p < 0.003) at 21 days (58.9 %) than at 14 days (55.0 %).  These results are similar to those found by other authors (Reis et al 1991; Fundora et al 1992).

In conclusion, acceptable improvements in crude protein content  and in NDF in vitro digestibility were obtained when the Brachiaria humidicola hay was exposed to the dry ammoniation method, using 40 g of urea in 200 ml of water/kg hay for 21 days.

References

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Sundstol, F. (1988). In: World Anim. Sci. B Disciplinary approach. Feed Science Chapt. 10. pp. 257-273.

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Received 5 June 2002

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