Treatment of Crop Residues and Other Low Quality Forage

Description Treatment of raw forage with relatively low nutritional value such as poor quality hay, straw and harvest residue enables its nutritive value to increase in phosphate content, energy value and quantities ingested by ruminants in proportions between 10 and 40 percent. This technique enables good utilization of untreated forage resources by livestock, with a technical advantage, ie. improved animal feed; particularly at the time when food resources are most deficient, and an environmental advantage by reducing, as far as possible, recourse to natural vegetation, with the risks of overgrazing that this entails. | Description Techniques Costs Targeted Livestock Systems Impact Context of Application Monitoring: EIA, Indicators References

Techniques

Two major types of treatment technique are used:

- Physical treatments, especially grinding (or chopping) are useful but are expensive in terms of energy. They improve the possibility of mixing the forage with chemical products or food supplements but do not alter the chemical value. They are used less and less, except for threshed hay used especially to supplement with ballast intensive ration concentrates.

- Chemical treatments consist of utilizing the following substances:

- Soda: this technique called dry food consists of chopping the hay and then mixing it with a quantity of soda varying between 40 and 60g/kg straw ; the straw is then piled up for 8 days to complete the reaction. This technique is virtually no longer applied, in favor of the following ones.

- Ammonia: anhydrous ammonia is used in a ratio of 50g per kg hay put in a haystack and covered with plastic film; the reaction lasts 1,5 to 2 months. This type of treatment is less dangerous than that with soda and also permits an increase in phosphorus content of the straw, but it requires an industrial storage shed, transport and use of ammonia (injection in the straw ricks).

- Urea: in most hot countries, supply of industrial anhydrous ammonia is a problem, hence the use of urea. Hydrolysis of urea, if total, leads to the formation of anhydrous ammonia (and CO2) in the weight ratio NH3/weight of urea equivalent to 34/60. Conditions for good ureolysis are :

- Rehumidification of straw at a rate of around 40 percent.
- An ambient temperature over 15°C,
- Compact forage so that the ammonia can spread properly.

A treatment of 4 – 6p100 urea (‘ to 6 kg for 100l water and 100 kg straw), which corresponds respectively to 2,5 to 4p.100 NH3, makes it possible to improve the food value of the straw to a level close to that obtained with anhydrous ammonia.

Costs

The cost of treating rice straw with urea is estimated at US$0.036 per kg.

Targeted Livestock System

Chemical treatment of forage requires additional work and inputs. It is suitable for responding to a need to intensify animal products stimulated by subsistence (milk), agricultural (draft animals) or commercial (milk and meat) requirements. This technology is not suitable when it is only a question of maintaining the herds.

Standing grass straw is the basic resource in two large regions:

- On the one hand the dry belt of the ancient world stretching from Mauritania to Mongolia.
- On the other, the semi-arid regions of the new world (America, Southern Africa and Australia), where European settlers developed extensive ranching systems.

Crop residues constitute the main forage resource for cattle in the heavily populated regions of tropical Asia, where every space is used for subsistence crops. They play an increasingly important role in intertropical Africa. Most of these residues are buried, burnt or used for litter.

Impact

- Positive environmental impact

- Utilization of raw forage reduces by the same amount recourse to vegetation and overgrazing in periods of forage shortage.

- Negative environmental impact

- Removal of straw and harvest by-products which protect the soil from erosion.
- Removal of straw and harvest by-products from production areas, increasing export of nutrients from cultivated plots and reducing soil fertility if there is no other organic restitution.
- Risk of artificial increase in animal load of a region beyond its natural carrying capacity dictated by the level of natural forage resources.

- Impact on livestock productivity

- The chemical treatment of poor forage alone improves animal production significantly, but is it more effective when linked in synergy with a supplement of concentrates, particularly energy (molasses).

Context of Application

- Satisfaction of an increasing demand for animal productions necessitates utilization of increasingly efficient food resources. In most pastoral and mixed systems, producers have therefore used several techniques to improve ingestion and digestibility of forage described as poor, such as hand-ground meal.

- It has been known since the beginning of the century that a soda treatment in liquid form improves grass digestibility. Industrial dry treatment appeared around 1970, following industrial dehydration of forage: and ammonia treatment has attracted most attention for the past ten years, following the work of the Scandinavians.

> - Favourable factors:

> > - Increase of forage deficit, particularly the seasonal shortage.
> > - Market demand for well-used animal products : milk, fattening, justifying the cost of treatment.
> > - Availability of inputs (ammonia, solder, urea).

> - Unfavorable factors:

> > - Extra work.
> > - Difficulties in input supply.
> > - Cost of inputs.

Monitoring: EIA, Indicators

- Rate at which the technique is adopted by livestock farmers
- Number of animals receiving treated forage,
- Productivity of animals which have received treated forage.

References

Demarquilly (Editeur), 1987. Les fourrages secs, Récolte, traitement, utilisation. INRA, Paris.

Molénat G., Chenost, M., Hubert D., Gouy J., 1995. Utilisation des ressources fourragères par les ruminants en régions chaudes. Ann. Zootech. 1996, 45, Suppl. 3: 3-140.

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