By Arnold Kanengoni, senior researcher, ARC
Compared to the amount of work done in protein research, little has been done in energy nutrition in South Africa. One possible reason is that there has always been a readily available source of energy in maize.This may however change due to the biofuel initiative where a substantial amount of the grain may end up being directed to ethanol production. A number of reviews have been published on alternative sources of energy for pig diets in South Africa (Kemm and Brand, 1996; Brand, 2000).
Sorghum (Kemm and Brand, 1996) has been touted as the grain crop to grow because it requires less moisture than maize, has the ability to continue to develop during droughts or serious moisture stress and has a higher production potential than maize on most soil types. Nevertheless, production of sorghum in South Africa still trails that of maize.
The results from comparing high and low tannin cultivars of sorghum with maize as the main grain component in the diets of growing pigs revealed that pigs fed low tannin sorghum performed equally well if not better than pigs fed a maize based diet, while the pigs fed high tannin sorghum had reduced weight gains and poor feed conversion (Kemm et al., 1984; Brand et al., 1990).
Subsequent work was done to reduce the tannin content using thermal ammoniation and heat treatment with significant improvements in ileal digestibility and nitrogen retention (Brand et al., 1989; Brand et al; 1990).
The other review was on studies done on alternative energy sources for pig production in the Western Cape (Brand, 2000). While maize is mainly grown in the northern parts of the country which have higher rainfalls and suitable temperatures, the southern provinces grow small grains more. Since maize becomes more expensive when transport costs are factored in, locally produced small grains were evaluated in a series of studies as alternative sources of energy to maize in pig diets.
Samples of locally produced grain sources like wheat, barley, triticale and oats were collected over a period of three years (1994 to 96) and determined for chemical composition, physical composition, digestible energy and quality (Brand et al., 1997; Brand, 1998; Brand, 1998). Crude protein and digestible energy content were affected by the presence or absence of hulls, with hulled grains containing less protein and energy than their hull-less counterparts. The value of crude protein generally compared well with maize.
Brand and Swart (1999) also undertook studies on the variation in the chemical composition of South African barley, as well as the relationship between energy value, chemical composition and physical properties.
Comparisons were made to predict the energy value of barley from physical properties or chemical composition. The study revealed considerable variation in the relationship between physical composition, chemical composition and digestible energy value of the barley for pigs. However, it also showed that both the physical and chemical properties can be used to predict the energy content of barley.
In a study carried out by Brand et al., (1996) the value of naked oats as an alternative to maize in diets of respectively weanling and growing/ finishing pigs was determined in two experiments. In both diets, maize meal and soyabean oilcake were gradually replaced with naked oats. The effect of naked oats on growing/finishing pigs was less than in weanling pigs and it was shown that the inclusion level of 49% may negatively affect growth traits.
As competition for grain intensifies, more and more attention is going to focus on co-products of biofuel production and agricultural by-products which had been ignored all along as sources of feed for pigs. In addition to a drive towards non-conventional crops such as cassava, one product that is increasingly receiving interest is glycerol. Glycerol is currently being used in the pharmaceutical and cosmetics industries and is very expensive.
It is produced in quantities of about 10% of the biodiesel produced and will be produced in huge quantities as more and more biodiesel is produced which will reduce its price. It has the disadvantage that the biodiesel produced in conventional biodiesel processing facilities is of very low purity. Methanol, sodium chloride and potassium chloride are compounds that can be found in crude glycerol as a result of current biodiesel processing techniques. Levels of these compounds must be monitored to prevent excessive amounts in pig diets.
Some studies done in Europe and America have revealed its potential as an energy source in pig and poultry diets since it is glucogenic and quite palatable. Whereas in the past it was used occasionally in small quantities to replace molasses in diets, the focus now is on using it in sizable quantities to provide energy. With increasing production of biofuels, livestock producers will be increasingly encouraged to be flexible in feedstuff choice.
Crude glycerol may play an increasingly important role in meeting the energy needs of pigs. At the same time the rapid pace of growth in ethanol production may limit pig producer’s access to maize. The Agricultural Research Council is undertaking a study to evaluate the potential of using glycerol in pig diets. With the current increases in maize prices and the expected drop in the prices of the glycerol as more and more of the product is produced, it is advisable to gain as much understanding of the product as possible before it can be safely used.