NUTRITION ▶▶▶
Particle size and its effect on gut health
Particle size is an important factor that determines feed efficiency and gut health in pigs. Feed processing therefore needs to evolve, with an increased focus on the complex interaction between pellet characteristics, gut health and microbiota.
BY ELIJAH G. KIARIE AND ALISHA MILLS, DEPARTMENT OF ANIMAL BIOSCIENCES, UNIVERSITY OF GUELPH, CANADA
A
Reducing the quantity of fine particles in pig feed is strongly recommended.
dvances in genetics have produced commer- cial strains of pigs with improved performance (growth, reproduction, etc.) based on minimal feed input. The nutrition for these animals has
also evolved over time to achieve and sustain their genetic potential. Examples of advances in monogastric nutrition include the widespread adoption of net energy, ideal ratios of standardised ileal digestible amino acids and digestible phosphorous concepts, enabling nutritionists to formulate cost-effective optimal diets. There is also increased interest in the interaction between feed processing and gut health in animals. A healthy gut is very important when raising pigs sustainably and profitably, with limited use of antibiotics.
The role of feed processing Today, most pig feeds are manufactured by using a com- bination of technologies, including physical grinding with
hammer and/or roller mills in conjunction with hydrothermal processing including pelleting, expansion or extrusion. Pel- leting is the most prevalent hydrothermal method for man- ufacturing pig diets. During the pelleting process, the feed is passed through steam, which softens the feed particles be- fore they are pressed through the die by the rolls in the pellet press, causing an additional grinding effect. It is well recognised that processing parameters such as the extent of particle modification, processing temperature, pressure, duration and water determine the physical and chemical reactions in and between nutrients as well as the adhesive properties on the feed particle surfaces, the final physicochemical structure and the hygiene status of the feed. Those attributes can directly and indirectly influence the im- pact of the processed feed on the digestive tract ecology and thus animal health, performance and feed cost. Some of the studies that examined the link between processed feed 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) nutrition. From an economic point of view, optimal particle size distribution adapted to the physiological needs of the animal enables optimal utilisation of nutrients and enhances animal per- formance. Numerous reports show the effects of cereal feed particle size on pigs (Table 2). Pigs fed a coarse diet have heavier stomachs than pigs fed a fine diet, which probably reflects the fact that coarse diets require more muscular action for processing by the stomach than fine diets. Feed particle size was also shown to impact the large intestine. Studies have demonstrated that coarse di- ets were strongly associated with higher propionic and butyr- ic acid levels in the caecum and colon contents. It is possible that coarse feed particle size may promote an increase in bac- teria populations producing short-chain fatty acids (SCFAs) and, thus, contribute to gastrointestinal health by preventing the proliferation and/or virulence of harmful bacteria such as Salmonella species and Escherichia coli. Studies have demonstrated that change in feed presentation could be associated with microbiota modification (different
52 ▶ PIG PROGRESS | Volume 38, No. 3, 2022
PHOTO: BERT JANSEN
PHOTO: SHUTTERSTOCK
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