Livestock Research for Rural Development 14 (2) 2002

Dung ash treatment of a native forage to improve livestock feeding in low-input Andean pastoral systems

Didier Genin, Percy Abasto*, Severo Choque** and Julian Magne**

Institut de Recherche pour le Développement (IRD ex-ORSTOM),
BP 434, 1004 Tunis-El-Menzah, Tunisia. (Corresponding Author)
* Pontifica Universidad de Chile, Santiago, Chile.
** Universidad Tecnica de Oruro, Oruro, Bolivia



Paja brava (Festuca orthophylla) is a coarse bunchgrass found widely in the Andean highlands. It is grazed intensively by range herbivores, despite its low nutritive value. The effects of treating paja brava with NaOH + urea and dung ash + urea on nutrient digestibility by llamas and sheep were investigated. Four comparative digestion trials were conducted using 1) fresh paja brava collected daily during vegetative growth (GPB), 2) dry standing paja brava collected during the dry season (DSPB), 3) paja brava hay treated with 3% NaOH and 3% urea (NaOH + urea PBH), and  4) paja brava hay treated with a 20% dung ash solution and 3% urea (DA + urea PBH) as feeds. 

For all treatments, digestion coefficients for dry matter were higher in llamas than in sheep. Alkaline treatments significantly improved dry matter digestibility, ranging, in llamas, from 44.7% for DSPB to 52.2% for DA + urea PBH, 54.2% for GPB and 60.7% for NaOH + urea PBH, and, in sheep, from 39.4% for DSPB, to 41.1% for GPB, 49.7% for DA + urea PBH and 55.8% for NaOH + urea PBH.

Nutrient digestion coefficients showed the effectiveness of the alkali treatments for improving the nutritive quality of this forage for both llamas and sheep. The effects of treatments on intake gave contrasting results depending upon animal species, with the highest levels for dung ash + urea treatment in llamas (43.7 g/kgW0.75/d) but for NaOH + urea treatment in sheep (56.3 g/kgW0.75/d).

The significance of these findings is discussed in relation to feeding management strategies for low-input subsistence farming systems.

Key words:  roughage treatments, sodium hydroxide, dung ash, urea, llama, sheep


Livestock production in the arid Andean highlands, such as the west and south Bolivian highlands, is sometimes the only possible agricultural activity due to the combination of frost and aridity, which largely hinder crop growth (mean annual rainfall 300 mm and 300 days of frost per year). In this adverse environment, people have developed livestock production systems highly adapted to local production constraints for millennia. Functioning of these pastoral systems appears to be oriented more toward optimising herbivore-rangeland relationships than introducing new forage sources or animal breeds. This assertion is supported by the necessity not to enhance and spread production risks, a very low cash mobilisation capacity, a high degree of geographical isolation, and socio-cultural traditions.

However, these original pastoral systems face an important crisis and their reproduction requires technical and socio-economic innovations. From a technical perspective, two main limitations have been found: a high sensitivity to major climatic events such as a prolonged drought or heavy snow falls, and very low productivity (Genin and Picht 1995).

Family herds of the arid Bolivian highlands are usually mixed, composed of llamas and sheep which feed exclusively on rangelands (Tichit and Genin 1997). These rangelands are dominated by coarse bunchgrasses from genera Festuca and stipa. For most of the year, they appear like straw, because of a very short growing period (3 to 4 months per year). One of them (Festuca orthophylla) is called by natives “ Paja brava ” (wild straw). This species accounted for up to 40 and 34% of the diet taken on a diversified pastoral territory during the dry season by llamas and sheep, respectively (Genin et al 1994). It can represent more than 90% of the winter diet of llamas in pampa areas. The chemical composition of paja brava shows that this species is very poor quality forage even in a vegetative stage.

Alkaline treatments of high fiber roughages have been investigated extensively, and there are numerous reviews of their effect in incrementing feeding value for ruminants (Jackson 1978; Wanapat et al 1985). The most common alkalis used are NaOH, Ca(OH)2 and urea-ammonia. Due to the low temperature involved in the environment where we are working, the use of urea is restricted to being a supplement for nitrogen and not as a chemical for treatment of forages. Sodium hydroxide is a prerequisite for illicit cocaine manufacturing, and so is highly regulated in Bolivia. The other chemicals are not easily available in the region. One economical alkaline source is wood ash. Nolte et al (1987) found that treatment of wheat straw with a 30% solution of wood ash for 6 h significantly increased dry matter digestibility (DMD) for goats. Ramirez et al (1992) confirmed these results and showed that the DMD of diets containing corn stover treated with 20% wood ash increased up to 20% in sheep, compared to a control group. Unfortunately, wood is very scarce in the arid Andes, only available from shrubs of very low growth and already intensively harvested for fuel.

Due to their high pH values, we hypothesised that ash from dung (DA) could have similar effects to wood ash. Dung is easily available in the Andean pastoral area because of the particular behaviour of camelids which defecate on very specific areas in the shape of heaps, and because it is not utilised for agriculture, nor for fuel.

In this paper, we explored the possibility of treating paja brava with dung ash, sodium hydroxide and urea for increasing its digestibility by llamas and sheep. It was the first attempt, as far as we know, to increase digestibility of a range forage using recycled animal by-products for the benefit of the same animals. This research was oriented towards proposing a technical alternative for feed management in very-low-input subsistence pastoral systems.

Materials and methods

Dung was collected from the heaps found in the proximity of the resting areas of camelids. It was provided by both alpacas and llamas, in an undetermined proportion. It was burned for two days in the vicinity. The ashes were dark to light grey and could have included several impurities such as soil. Paja brava  was hand-harvested in the late growing period (February to March), air-dried, chopped to lengths of approximately 10 cm, and stocked in a dry area for further treatment. Due to its very low nitrogen content (4.8 g N/kg DM), PBH was supplemented after alkali treatment with urea in order to increase the crude protein (CP) content to 7%.

Four digestion trials were conducted, using three 4-year-old male llamas averaging about 90 kg in body weight, and three 2-year-old castrated criollo sheep of about 21 kg. The animals were housed in metabolism cages for 16 days and were fed paja brava ad libitum in different forms:

The experiment consisted of a 10-day adjustment period followed by a 7-day faecal collection. Feed was offered twice daily (07:00 and 14:00). Faeces and feed residues were weighed daily, and a 10% aliquot was composited across days for each animal for further analysis. 

Treatment with sodium hydroxide and urea followed the procedures used by Jackson (1978). It consisted  of spraying a 40% NaOH solution (w/v) on the PBH to give a final concentration of 3% NaOH (DM basis), and storing for 3 days in polyethylene bags. After 2 days of outdoor drying, the hay was treated with a 40% urea solution following the same procedures in order to obtain a final concentration of 3% urea in the PBH (DM basis), and stored for 21 days in polyethylene bags. After two days of outdoor drying, the treated material was ready to use.

Treatment with dung ash followed the procedure proposed by Nolte et al (1987). PBH was soaked in a solution containing 20% (w/v) dung ash, according to the procedure recommended by Ramirez et al. (1992) for wood ash. Approximately 200 litres of DA solution were used to soak sequentially five batches (about 35 kg each) of PBH for 6 hours. After soaking the PBH was dried outdoors for 3 days, and 3% urea (DM basis) was added, following procedures described above.

Feed, feed refusals and faeces were analysed for dry matter (DM), organic matter (OM), ash and CP by standard procedures (AOAC 1980). Neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) were analysed according to Van Soest (1973) and Van Soest et al (1991). The concentration of minerals in dung ash was determined by atomic absorption spectrophotometry.

Data from the digestion trials were evaluated by a two-way analysis of variance procedure. Treatment means were separated using a Neuman-Keuls test when treatment effects were significant (P<0.01).

Results and discussion

Chemical composition of dung ash

Solutions with 20% concentration (w/v) of DA in distilled water had a pH value of 10.4. Mineral analyses of DA showed the following composition (in g/kg): P 1.4; K 4.8; Ca 6.0; Mg 1.5 and Na 2.5. The chemical composition of dung ash has not been reported previously. Compared to composition of  wood ash used in the experiments of Nolte et al (1987) and Ramirez et al (1992), DA had very low values  for Ca and Mg  and a slightly higher value for P. The reported values are within the ranges found for livestock dung in tropical regions (De Rouw et al 1998).  

Chemical composition of paja brava: effect of treatment

Chemical analyses showed that both alkali treatments reduced the OM content of paja brava (Table 1). This was presumably due to the significant addition of minerals to the ash fraction, which would also result in a decrease in the fibre components of the treated straw.   

Table 1. Chemical conposition (in % DM) of untreated growing paja brava (GPB), dry standing paja brava (DSPB), and alkali-treated paja brava hay (NaOH+urea PBH and DA+urea PBH)

























NaOH+urea PBH






DA+urea PBH






The CP of untreated PBH did not meet nitrogen requirements for either sheep or camelids (San Martin and Bryant 1989), whereas the treated material presented CP concentrations of 6.5% for NaOH+urea PBH and 10.6% for DA+urea PBH. These latter values barely meet maintenance requirements or, in the case of DA+urea treatment, provide only for a low level of production. The nitrogen content of NaOH+urea PBH was significantly lower than that of DA+urea PBH in spite of the same urea supply. This could reflect a loss of urea-N due to hydrolysis to ammonia on the more alkaline NaOH treatment.  

Paja brava appears to be a typical material for alkali treatment, in terms of its high concentration of hemicellulose (the difference between NDF and ADF) which is known to be significantly solubilized by alkali exposure. Compared to untreated hay, NDF concentration for NaOH-treated PBH was reduced by about 12%, and was within the ranges found in the literature (Moss et al 1990). NaOH treatment also dissolved a portion of acid-detergent lignin (ADL), as reported by Jackson (1978). DA+urea treatment had an overall lower effect on fibre fractions of PBH than NaOH+urea. Nolte et al (1987) found a similar pattern of results comparing the effects of wood ash and NaOH treatment on wheat straw.  

Digestion trials

For all treatments, digestion coefficients of all nutrients except for CP were higher (P<0.01) in llamas than in sheep (Table 2). For example, differences in DMD between these two animal species were 13.1, 5.3, 4.9 and 2.5 percentage units for GPB, DSPB, NaOH+urea PBH and DA+urea PBH, respectively. These results agree with the ones obtained by San Martin and Bryant (1989) and Genin and Tichit (1997), who mentioned that the less degradable the forage, the greater the difference was between the two animal species. Alkali treatments, especially NaOH+urea, significantly improved digestibility of DM, OM, NDF, and ADF, both in llamas and sheep. These results confirm the general findings of Sundstol and Owen (1984) that NaOH is more effective than other chemical treatments in improving the potential digestibility of straws. In contrast, Ramirez et al (1992) found that the improvement in digestibility of alkali-treated corn stover was greater when treated with 20% wood ash solution than when treated with 4% NaOH, both in sheep and goats. Gihad et al (1981) pointed out that degradability of roughages was variety-specific, which may suggest qualitative differences in cell wall constituents and/or in their chemical and physical associations. Following the roughage classification proposed by these authors, PBH is an intermediate lignin roughage (10 to 15% lignin content), whereas roughages utilised by Ramirez et al (1992) and Nolte et al (1987) were low lignin roughages (less than 10%). Apparent ADL digestibilities found in this study should be examined with caution. Discrepancies in estimates of ADL could result from solubilization of lignin throughout the digestive tract with formation of phenolic matter, some loss of immature lignin or failure to recover finely-divided lignin in faeces (Van Soest 1994). The negative value of CP digestibility found for DSPB could be explained by a very low nitrogen supply and a subsequent mobilisation of animal tissues.

Table 2. Dry matter intake (g/kgW0.75/d) and apparent digestion coefficients (%) of untreated growing paja brava (GPB), dry standing paja brava (DSPB), and NaOH+urea and dung ash+urea treated paja brava hay (NaOH+urea PBH and DA+urea PBH) in llamas and sheep.







NaOH+urea PBH





NaOH+urea PBH


Digestion coefficients (%)





























































Intake (g/kgW0.75/d)

















abc Means in the same row, by animal species, without a common letter differ (P<0.01).

Intake of untreated paja brava was low (Table 2), compared to levels of intake previously reported by San Martin and Bryant (1989) for conventional forages such as alfalfa or barley hay.  The effect of alkali treatments gave contrasting results for the two animal species involved. Llamas presented a reduced level of intake of PBH treated with NaOH+urea PBH compared with PBH treated with DA+urea. This latter level of intake was similar to the one found by Cordesse et al (1992) for llamas consuming wheat straw treated with NH3.  Intake of PBH treated with NaOH+urea was comparable to data found by Cordesse et al (1992) for sheep consuming NH3-treated wheat straw and greater than the intake found by Moss et al (1994) for different NaOH treated straws (39 to 45 g/kg0.75/d). Intake of PBH treated with DA+urea by sheep was very low, similar to that found using untreated DSPB, and slightly higher than data reported by Moss et al (1994) for sheep consuming different untreated straws (24 to 30 g/kg0.75/d). These data are difficult to interpret given our current state of knowledge, but the smell and taste of the products, and source of the dung ash could have influenced these differential patterns of intake by animal species. It should be noted that this study was performed using sub-maintenance or medium quality diets, as observed during the dry season in the arid Andean highlands, and should therefore be repeated at more standardized planes of nutrition, specially concerning N supply.

Live weight changes of the animals during the experiments showed that llamas gained daily an average of  115 g when fed with DA+urea PBH, similar to a diet constituted of fresh growing paja brava (+140 g/d) (Genin et al 1994). Treatment with NaOH+urea resulted in a lower weight gain of 83 g/d in llamas as a consequence of the low daily intake. Sheep showed weight gains only when fed with NaOH+urea PBH. Due to the short period involved in the experiment, these live weight changes should be taken with caution. However, they were confirmed by results of an unpublished experiment on supplementing free-ranging lambs with NaOH+urea PBH for two months during the dry season (Choque 1995).


Dung ash plus urea treatment of paja brava hay provides a forage of an average quality comparable to alkali-treated straws, and the treated hay can be a very useful security forage in the arid Andean highlands for feeding strategies of livestock during the frequent periods of scarcity. This technical alternative seems particularly adapted to the economic conditions of the low-input subsistence farming systems found in this region. However, further investigations are needed in order to evaluate its feasibility and effectiveness in the local livestock production systems, particularly in relation to labour availability, and to determine levels of land-use pressure to ensure the sustainability of the resource.


This study was carried out within a collaborative research program between the Bolivian Institute of Agropastoral  Technology (IBTA) and the French Institute of Research for Development (IRD, ex-ORSTOM) entitled “ Dynamics of production systems in the Bolivian highlands ”. Thanks are due to the Corporación para el Desarrollo de Oruro (CORDEOR) for facilities to conduct experiments at Turco Station, and to Ph. Newell and H Guerin for reviewing the manuscript.


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Received 14 February 2002

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