Particle size and its effect on gut health
Advances in genetics have produced commercial strains of pigs with improved performance (growth, reproduction, etc.) based on minimal feed intake. The nutrition of these animals has also evolved over time to reach and maintain their genetic potential. Examples of advances in monogastric nutrition include the widespread adoption of net energy, standardized ideal ileal digestible amino acid ratios, and digestible phosphorus concepts, allowing nutritionists to formulate optimal cost-effective diets. There is also growing interest in the interaction between food processing and gut health in animals. A healthy gut is very important for raising pigs sustainably and profitably with limited use of antibiotics.
The role of food processing
Today, most pig feed is manufactured using a combination of technologies including physical milling with hammer and/or roller mills in conjunction with hydrothermal treatment including pelleting, expanding or extrusion. Pelletizing is the most popular hydrothermal method for making pig feed. During the pelleting process, the feed is passed through steam, which softens the feed particles before they are pressed through the die by the rollers of the pellet press, causing a grinding effect additional.
It is well recognized that processing parameters such as extent of particle modification, processing temperature, pressure, time and water determine physical and chemical reactions within and between nutrients as well as adhesive properties. on the surfaces of the feed particles, the final physicochemical structure and the hygienic state of the feed. These attributes can directly and indirectly influence the impact of the processed feed on the ecology of the digestive tract and therefore on animal health, performance and feed cost. Some of the studies that have looked at the link between processed foods and health effects are listed in Table 1. Effects of smaller particle size include increased stomach ulceration in pigs.
The effect of particle size
Grinding makes it possible to create different particle sizes. Particle characteristics, particularly size, are one of the most controversial issues in pig (and poultry) feeding. From an economic point of view, an optimal particle size distribution adapted to the physiological needs of the animal allows an optimal use of nutrients and improves the performance of the animal. Many reports show the effects of grain feed particle size on pigs (Table 2).
Pigs fed a coarse diet have heavier stomachs than pigs fed a fine diet, probably reflecting the fact that coarse diets require more muscle action to be processed by the stomach than fine diets. Food particle size has also been shown to impact the large intestine. Studies have shown that coarse diets are strongly associated with higher levels of propionic and butyric acid in the cecum and colon contents. It is possible that food particle size promotes an increase in populations of bacteria producing short-chain fatty acids (SCFAs) and thus contributes to gastrointestinal health by preventing the proliferation and/or virulence of harmful bacteria such as Salmonella species and Escherichia coli.
Reduction in the amount of fine particles
Studies have shown that the modification of feed presentation could be associated with a modification of the microbiota (different composition and/or metabolic activities) in the gastrointestinal tract of pigs. According to literature data, reducing the amount of fine particles in pig feed is strongly recommended. Generally, based on the existing literature, the amount of finer particles (1.6 mm) should also be low due to reduced nutrient use. The proportion of medium-sized particles (>0.5 to
The benefits are beyond doubt
The benefits of animal feed processing in terms of animal performance and economics are beyond doubt. However, as pig production practices evolve, feed processing diets will no longer only be valued in terms of optimizing nutrient utilization, but also in terms of impact on the hygienic condition of the feed, the effectiveness of feed additives, animal health and food safety. Pet food processing must accommodate an increasing focus on dietary approaches (ingredients and physical characteristics) to maintain a healthy and functioning gastrointestinal tract.
Understanding the mechanisms involved in the complex interactions between diet, gut microbiota, and gut tissue can help support gastrointestinal tract function and health through targeted dietary modifications. The optimum particle size could be engineered in the grinding process using a roller or hammer mill.
However, since most pigs are fed hydrothermally treated diets, further reduction in feed particle size is inevitable. Because fine grinding is generally preferred for high quality pellets, and because it is difficult to avoid further reduction in feed particle size during the pelleting process, a fine particle size will be almost inevitably found in pelleted feeds.
Modified extrusion process
The options for reducing the intensity of particle crushing during granulation, by varying the parameters of the granulation process, are very limited. A modified extrusion process (i.e. treatment using an expander) followed by a shaping element as applied in the pet industry could be an alternative to pelleting to preserve particle size. Strategies such as the addition of concentrated fibrous matter may be more appropriate in pelleted feeds, but data are largely lacking on its applicability in practical diets.
This article is edited from the original article: Role of Feed Processing on Gut Health and Function in Pigs and Poultry: Conundrum of Optimal Particle Size and Hydrothermal Regimens, published in Frontiers in Veterinary Science (2019,6:19).