To combat rising grain prices, in addition to minimizing the effects of animal production on the environment, efficient utilization of grain is extremely important. Biotechnology through solid-state fermentation (SSF) provides a method for producers to address these concerns.
The fermented product of SSF is particularly suited for animal feed applications for three important reasons: 1) the microorganism is able to liberate energy from the fiber portion of grain, improve the digestibility of protein, and release phosphorus bound as phytate in feed with a single fermentation; 2) the endogenous enzymes the microorganism produces are unique from the ones found in the digestive tract of animals; and 3) the fermented product is adapted to particular substrates used for production, and thus the types of materials included in animal feed.
Substrates are commonly agro-industrial residues, which are often used as feed ingredients themselves such as wheat bran, distillers dried grains with solubles (DDGS), soybean hulls, or rice bran. As the organism grows and utilizes the substrate for itself, the endogenous enzymes work in synergy to break down the substrate. The SSF complex improves the overall utilization of feed by assisting animals in breaking down the contents of their diet further than they would be able to alone. This enables producers to reformulate diets and save on raw material costs.
Utilization of grain
The utilization of grain by animals is far from achieving complete efficiency. Swine, for example, are unable to digest 15% to 25% of the food they consume [Sheppy, 2001]. One of the main limitations of monogastric animals is their inability to digest fiber. Fiber consists of non-starch polysaccharides, cellulose and hemicellulose, in addition to pectin and lignin, which are complex structural compounds integrated with cellulose and hemicellulose. Fungal organisms made from SSF are capable of breaking down cellulose and hemicellulose to utilize the sugars, or energy contained within. The addition of the fermented product of SSF to animal diets releases more energy from the fiber portion of the diet, which equals savings to the producer, allowing them to reduce the amount of additional energy sources. These vary in source and cost depending on the region of the world.
There is also considerable variability in the quality and the availability of protein from the raw materials typically found in the diets of monogastric animals. This is an important consideration as nutritionists aim to meet the amino acid requirements of animals. Supplementing animal diets with the products produced from solid-state fermentation increases the digestibility of protein making it easier to meet the animals’ requirements. The addition of a protease-containing product, such as those produced from SSF can assist the animals in hydrolyzing protein molecules into smaller, more absorbable fractions [Cowieson and Adeola, 2005].
Finally, swine are unable to digest a considerable amount of the essential mineral phosphorus in the form of phytic acid found in the raw materials of vegetable origin. The adverse effects of phytate on the availability of phosphorus and other nutrients have been acknowledged for many years [Cosgrove, 1966].
Complex matrices
The complex matrices that make up feed ingredients can limit the availability of nutrients to the animal. A contributing factor is the chelating capacity of phytate, which may form complexes with minerals, starch, and protein [Selle et al., 2000].
By supplementing diets with a product such as those produced from SSF, nitrogen excretion can be reduced by up to 15% for pigs, and similar reductions can also be achieved with phosphorus [Sheppy, 2001]. This has obvious environmental advantages and translates into savings for the producer by reducing the amount of phosphorus supplemented. The addition of phosphate salts is problematic since most of the phosphorus is not absorbed by the animal and thus, is excreted causing environmental concerns.
Commercial trials
A number of commercial trials have been conducted to quantify the effects of SSF when supplemented for swine diets in various parts of the world. In a grower pig study conducted at China Agricultural University [Qiang and Wang, 2004], for example, SSF was added to a wheat-soy diet formulated to contain 90 kcal less per kg and 0.15 % less available phosphorus than widely accepted levels for swine in China. The SSF-supplemented diet resulted in improved feed conversion ratio and average daily gain compared to the control. In Switzerland, a study was completed examining the effects on growing and fattening pigs fed standard wheat and barley diets also challenged with available phosphorus and digestible energy [Taylor-Pickard and Suess, 2007]. The results are presented in Table 1.
Average daily gain for the whole period fed was 27 kg greater and carcass weight 5 kg heavier for the SSF-supplemented diets versus the control. The improvements may be attributed to increased energy availability. Harnessing fungi’s ability to do break down fiber, improve the digestibility of protein, and make phosphorus more available to the animal through solid-state fermentation is improving the overall the utilization of feed and minimizing the impact on the environment.