The objective of straw treatment is to increase digestibility and/or voluntary consumption, thus increasing the intake of digestible energy. The grinding of straw increases consumption leading to higher digestible energy intakes of the order of 30%. In terms of net-energy intake the increase is somewhat more than this because the net-energy value of straw is increased by grinding. Even then, it is only about one half as effective as alkali treatment. There is a small additive effect of grinding and alkali treatment on the intake of dry-matter, but this effect has not been evaluated nutritionally or economically. Several types of white-rot fungi have been found which digest lignin in wood to a greater extent than carbohydrates, thus producing a material (partially-digested straw + fungus) of enhanced digestibility with only a small loss of carbohydrates. Further studies of the use of these organisms as a method of straw treatment should be taken up.
A variety of methods of treating straw with alkalis--NaOH, NH3 and Ca(OH)2--have been developed. These vary in cost of treatment, effectiveness and suitability for different situations. They are broadly classified into soaking (wet) methods and spray (dry) methods. In the former the straw is soaked in 10 or more litres of a 1.5% NaOH solution/kg straw and washed in a closed system from which water is not discarded. A wet straw is produced with a sodium content of about 2%. Organic matter digestibility increases by 20 percentage units for an expenditure of 4–5 kg of NaOH/100 kg straw. Dry methods increase digestibility by 15 units with 4–5 kg NaOH if heat is applied; otherwise the increase is only about 10 units. When dry-treated straw is the main component of the diet, the level of NaOH/100 kg straw must be limited to 4–5 kg to avoid stress to animals from sodium. Higher levels of 7–9 kg/100 kg straw can, however, be used to obtain still greater increases in digestibility when straw constitutes only half of the diet. Ca(OH)2 is as effective as NaOH, but, because it is less soluble, reacts more slowly and Ca(OH)2-treated straw must therefore be ensiled for 4–5 months. NH3 is less effective than NaOH, the maximum increase in digestibility being about 12 units. This is achieved with 3–4 kg. NH3/100 kg straw at ambient temperatures and treatment periods of 2–8 weeks. Heating does not appear to improve the efficiency of NH3 treatment. Detailed descriptions of each method are given in this report and each method is critically evaluated.
The initial digestibility of straw varies between 35 and 55%. Treatment increases this by 10–20 units depending upon the method used, the extent of increase among straws being more or less independent of initial digestibility. Thus treated straw varies widely in digestibility, and this variability is as much as is encountered in hay and silage. For efficient utilisation, farmers will have to be advised individually on the use of treated straw as they are for hay and silage; i.e., the digestibilities of individual lots of treated straw will have to be determined by in vitro techniques by the advisory service and feeding recommendations made to suit the quality of the straw. Factors which affect initial digestibility are specie, variety, year, and method of handling.
The digestibility of treated straw can be depressed if it is fed in diets with more than about 30% concentrates, as is the digestibility of all roughages. In general this depression is greater with highly digestible roughages than with those of lower digestibility. With straws this means that in high-concentrate diets the digestibility of treated and untreated straws often become the same; i.e., there is no benefit from treating straws used in high-concentrate diets. An exception to this appears to be if treatment is done with a larger amount of alkali--7–9 kg NaOH/100 kg. The high alkalinity of the straw probably counteracts the tendency with such diets for the pH of the rumen contents to fall and thus ensures the maintenance of conditions favourable to the activity of cellulolytic organisms.
Treated straw can replace hay or silage in the diet if the difference in protein content between the treated straw and the hay or silage is made good with an oil meal supplement. In Southern Asia where straw is the mainstay of the diet, weight gains in growing cattle and buffaloes can be increased by 0.2 – 0.3 kg/day by treating straw and supplementing it with protein or even urea. In village stock this means at least a doubling weight gain and a sizeable reduction in age at first calving.
The substitution of farm-treated straw for hay and silage in the livestock
diet in Europe is profitable if the cost of untreated straw is only the cost of
collecting it from the field or where market prices do not greatly exceed
Substituting treated straw for cereal grains in the livestock diet in Europe is not profitable at present prices. The economics of factory-processed straw are not yet clear. In those countries where straw is traditionally fed to livestock treating it is clearly profitable.
The highest priority in research needs to be given at present to the utilisation of treated straw. Systematic study of the factors affecting the digestibility of straws, treated and untreated will provide the information needed to ensure that straw is fed to maximum advantage under all circumstances. The need for greater information in this matter of utilisation applies to roughages in general and not only to straw.
Equally important is the need to determine, in physical and economic terms, the benefit of alkali treatment of straw under village conditions in Asia and other areas where straw is the staple feed. This cannot be realistically determined on the experiment station. Further, if straw treatment is ever to be taken up on farms in Asia, its use will have to be demonstrated on farmers' animals, in the way that new crop varieties or agronomic practices are demonstrated on his fields. To meet both needs, the consultant proposes a “Field testing and demonstration project”. Details of this proposal are given in section VI.
Next in importance is the further testing and comparing of methods of treatment, and the development of cheap, efficient methods of handling and treating straw on the farm. An attempt should be made to devise systems in which existing farm machinery can be used.
In Europe, the economics of changing farming systems to accomodate straw utilisation need to be studied.