Crop and Industrial By-Products:
Cereals

Cereal grains are the main ingredients in pig and poultry feeds, and a source of energy in commercial feeds and supplements used for cattle and sheep. When cereal grains are processed for human consumption, by-products are produced that can be used in livestock feeds. For example, after wheat is milled into flour, more than one quarter of the grain becomes available as a by-product. These leftovers include bran and coarse middlings, which are usually fed to cattle and sheep, and fine middlings which are used in pig and poultry feed.

Straws and Stovers Bran and Polishings Brewing and Distillery Residues

Straws and stovers are highly fibrous feeds with a low protein content and very low digestibility. They are unable to provide even the maintenance requirements of sheep and goats unless they are supplemented or treated in some way to increase the supply of protein to the animal. They are unsuitable as feeds for pigs, poultry and rabbits. The leaves of straws are slightly more digestible than the stems, and if sufficient straw is offered so that the animals can select the only the more nutritious parts, then sheep and to a lesser extent goats will select the leaves and reject the stalks and thereby survive slightly better than they would if they were forced to consume all of the straw.

Goats are better adapted to eating browse rather than grazing, and it might therefore be expected that goats would eat more straw than sheep, and would survive better on a straw-based diet than would sheep. However, a study in Cameroon showed that sheep ate more straw than did goats, with the goats suffering much higher mortality because of their low intakes of straw.

Toxins

Rice straw has a high concentration of oxalic acid. Soaking the straw in water before feeding it to sheep and goats will remove much of the oxalic acid, and therefore make it safer to feed.

Chemical composition and nutritive value

The chemical composition and nutritive value of straws and stovers commonly used in the tropics are presented in the table below. Clearly, the concentration of nutrients in straw is extremely low, and the very low digestibility makes the nutritive value of straws even lower.

Estimates of chemical composition and nutritive value
of cereal residues for sheep and goats.

ME: metabolizable energy.

Treating straw to increase its nutritive value

When straws form a large component of the diet, the rumen micro-organisms grow very slowly because of the low availability of either energy or protein. This in turn lowers the digestibility of straw still further, as it is only in the rumen that the straw will be digested. Straw digestibility is increased a little (although the amount of feeding value obtained from straw is still extremely low) if the rumen micro-organisms are provided with some readily available energy and protein, so that they are able to grow. The increased microbial population is then able to digest the straw to a slightly greater extent. This is the rationale behind either treating straw with urea (to provide N for the rumen microbes) or supplementing the diet with protein, urea or (preferably) both urea and molasses.

There has been a considerable amount of work done on the urea treatment of straw. The recommended treatment rate is 40 g urea/kg straw with the urea usually being added as a solution in water (40 g urea/l water) which is then sprinkled on the straw. The straw may then either be fed straight away, or ensiled to enable the urea to degrade the fibre to some extent. If the urea treated straw is fed straight away, then straw digestibility is increased by about 5 units, whereas if it is ensiled for ten days, the increase in digestibility is twice this. However, although there is considerable evidence of the beneficial effects of treating straw with urea, the uptake of this technology in all areas has been extremely low. A number of reasons have been given for this, which include:

1. The cost and availability of the urea
2. Lack of knowledge of the technology
3. Lack of benefit observed in farm situation
4. Difficulty of practicing technology.

It should also be noted, when using this technology to improve the feeding value of straw for goats, that goats are extremely susceptible to urea toxicity and will die from urea toxicity at much lower dose rates than is the case with large ruminants such as cattle and buffalo. It is therefore important that if straw is treated with urea, the urea solution is dispersed throughout the straw, and no ‘hot spots’ of high urea concentration are produced.

A more applicable technology, perhaps, for smallstock keepers is to use straws and stovers as only a small part of the diet for sheep and goats (since they will need other supplementation anyway to meet their maintenance requirements). Supplementing the diet with green forage or legumes that will provide some protein will stimulate microbial growth in the rumen, and increase the digestibility of the straw to some extent. Cakes and meals from the processing of oilseeds (either industrially or on the farm) can also be used to help balance a straw-based diet. However, again, care should be taken when feeding these residues as they often contain a number of anti-nutritive factors.

 

When smallstock keepers live near to a rice or maize processing mill, they may have access to the bran and polishings that are produced as a by-product of the grain or flour manufacture. However, the market for rice bran in the west is increasing and so larger mills are likely to export most of their bran rather than sell it locally.

Depending on the process used, variable amounts of germ may be included in the polishings and bran, and there is also a reasonable amount of oil in rice bran as well. Despite a relatively high fibre content, therefore, bran is suitable for feeding to pigs (except very young pigs) and also to poultry in small amounts. The price and availability of these feeds is likely to vary with season, but they may be useful additions and supplements to the livestock diet at certain times of the year.

The composition of rice bran is given below.

Chemical composition of rice bran

By-products of the brewing and distillery industries include the leftovers once the starch has been removed from the grain during the malting and mashing processes. They can be fed dried or fresh to ruminants, or they can be conserved as silage. Distillers' grains must be treated before feeding to cattle. Malt culms or sprouts, another by-product, and dried brewers' yeast may also go into feed.

Residues from brewing and/or distilling cereals may either be industrial by-products, or products from home production of brewed or distilled liquor. If the latter, it is likely that the starch extraction and fermentation process is less complete and so the residual starch content of the feeds is likely to be higher than would be the case with by-products derived from a factory. This means that the energy content of brewing and distillery residues derived from home production is likely to be higher than similar by-products produced industrially.

When cereals are fermented for alcohol production, they are first malted and then mashed. During the process of malting the grain is partially germinated, converting the starches in the grain into sugars. The germination process is halted by drying the sprouted grains and the small rootlets, or Malt culms, formed during this process are also dried and can be used as livestock feed. Mashing is the process of extracting the fermentable sugars from the malted grains by stepping them in hot to boiling water for several hours. During the mash, enzymes in the malt convert the starches into fermentable sugars, a process known as saccharification. The resulting liquid is cooled and yeast is added. The yeast then ferments the sugars to alcohol.

Brewers' Grains

These materials are considered to be good sources of un-degradable protein and Water Soluble Vitamins and are used in feeding both ruminant and monogastric livestock.

The grains that are left from the malting and mashing process (brewers' or distillers' grains) will contain variable amounts of starch, and higher concentrations of protein and fibre than was the case with the original cereal. The chemical composition and feeding value of the grains depends on the cereal from which they were derived (barley, wheat, corn, etc.) and the efficiency and type of the malting and mashing processes. The contents are therefore extremely variable, but as a general guideline, they can be reckoned to contain approximately 200 g crude protein/kg dry matter (obviously much less than this on an as fed basis) and between 400 and 600 g neutral detergent fibre/kg dry matter.

Unless the brewers' or distillers' grains are either dried or ensiled, they will decompose very quickly and so should be fed quickly. They can be fed to sheep, goats and pigs. Their fibre content is too high to make them suitable for poultry.

Malt Culms or Malt Sprouts

The fibres of malt culms are highly digestible and are a useful constituent of livestock feed. Their value is greater for ruminants than for monogastric animals because only about half of the crude protein is digestible true protein. As dried malt culms swell in the stomach, the amount fed daily should be limited. The quality of malt culms is variable and only those in good condition and free from mould should be used. Malt culms are bitter and are sometimes refused if fed alone. (Source: AFRIS: Animal Feed Resources Information System, FAO).

Chin, F.Y. (2002). Ensilaging of tropical forages with particular reference to South East Asian systems. Paper presented at the XIIIth International Silage Conference, 11-13th September, 2002. [this paper includes Internet links to additional references]

Cramb, R. and Purcell, T. (2001). Developing Forage Technologies with Smallholder Farmers: How to Monitor and Evaluate Impacts. ACIAR Working Paper Series, No. 41