Expanded diets for swine: nutrient utilization
According to the Brazilian Animal Protein Association (ABPA) (2023), Brazil is the fourth-largest producer of pork in the world, with an estimated production of 4.8 million tons in 2022.
When analyzing the production costs in Brazilian swine farming, we observe a significant impact from the inputs that make up the feed, mainly corn and soy, which together account for more than 60% of the effective operating cost (EOC) (CNA, 2022).
In this context, feed processing plays a crucial role in swine farming.
One such technique is expansion, which aims to improve nutrient utilization (Teixeira Netto et al., 2019). This method increases the enzymatic activity of amylase, responsible for hydrolyzing the starch molecule into simpler, soluble carbohydrates, allowing greater water absorption and thereby enhancing the digestibility coefficient of the ingredient (Lima et al., 2016).
This process is carried out before pelletizing because it improves pellet quality (Teixeira Netto et al., 2019) and can be used for both complete diets and individual ingredients (Rojas and Stein, 2017).
Some processes, such as grinding, for instance, break the seed cuticle but typically have little effect on the protein matrix or its solubility.
More complete utilization requires a greater degree of starch granule disruption, which can be achieved through steam processing and pressure. Therefore, treatments involving moisture, heat, and pressure can enhance its efficiency (Germany, 1992).
Therefore, expansion leads to more intense modifications in the physical structures of the ingredients, improving pellet quality and consequently resulting in enhanced growth performance (Nemechek et al., 2015; Muramatsu et al., 2016).
However, with excessive processing, free amino groups in proteins react with carbonyl groups from reducing sugars, forming enzyme-resistant inter- and intramolecular bonds, known as the Maillard reaction. This reaction reduces both solubility and digestibility of the protein (Veloso et al., 2005), which is undesirable in processing.
Understanding the Expansion Process
Food processing through expansion causes physical changes to starch, such as gelatinization, which involves the release of amylose and amylopectin due to the breaking of hydrogen bonds, and the disruption of cell walls, facilitating enzymatic digestion (Van Soest, 1994).
Additionally, it offers other advantages, such as reduction of pathogenic microorganisms, inactivation of heat-labile antinutritional factors, increased digestibility of dietary components through enhanced surface area, and improvement of sensory quality of the food (Veloso et al., 2005).
In the expansion method, temperatures of 90 to 120°C are used for two to three seconds, followed by strong compression of the material. Subsequently, it is exposed to atmospheric pressure, resulting in high-density food (Fancher, 1996).
In the expander, the feed is forced by a screw to flow through a hollow cylinder, which has a hydraulically controlled cone that partially restricts the feed, creating intense frictional force and pressure (30 to 40 bar). With the addition of steam, heat is generated.
The release of pressure and spontaneous evaporation of water causes the feed material to expand in volume and rapidly decrease in temperature (Almeida, 2023).
Studies on the gelatinization process indicate that starch granules swell and break more easily in the presence of water contents above 40%, and that higher temperatures are needed when the water content is lower (Souza et al., 2000).
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In cereals, the physical expansion of starch granules begins between 50 and 60°C, while in legumes, it starts between 55 and 75°C (Mendes, 2002; Mendes et al., 2004).
However, there are differences in the degree of gelatinization among foods, which is proportional to the amount of amylopectin present, and varies depending on raw materials, processing conditions, and the degree of grinding of the foods (Ostergard et al., 1989; Peisker, 1994; Tomas et al., 1994).
Expansion in Swine
To evaluate the effects of ingredient expansion in swine feed, it is essential to use analytical techniques that allow for the estimation of nutrient quality and composition.
The enzymatic technique described by Karkalas (1985) is used to measure starch gelatinization. According to Peisker (1994), the ideal range of gelatinization is 35 to 50%.
This same study showed that enzymatic digestion of the starch in the expanded material releases the protein fraction to be used by the animal, with a trend toward higher digestibility of crude protein (CP) in the expanded soybean meal (41.25%) compared to non-expanded soybean meal (37.73%).
In Figures 1 and 2, you can observe the difference between the starch granules of corn that have been expanded or not expanded. This demonstrates that, if not subjected to expansion, the material tends to have a higher quantity of intact granules.
In Figures 3 and 4, the soybean meal and expanded soybean meal are shown. There is a noticeable lower proportion of starch granules in these foods and a lower degree of gelatinization in the expanded soybean meal (Veloso et al., 2005).
However, the authors noted that pigs fed diets containing DDGS showed even greater feed efficiency when subjected to conditioning by expansion (Feoli et al., 2008).
When studying the chemical composition and nutritional value of soybean subjected to different thermal processes for growing pigs, Mendes et al. (2004) found higher digestible energy values for expanded whole soybean compared to soybean meal, with 3803 kcal/kg and 3583 kcal/kg, respectively.
The same was found for gross energy, with expanded whole soybean showing a value of 5061 kcal/kg compared to 4204 kcal/kg for soybean meal.
The authors also assessed the digestibility of dry matter, crude protein, and gross energy and found lower values for expanded whole soybean, which may be attributed to inadequate processing.
| Low-quality pellets do not withstand the forces of friction, impact, and pressure during storage, transportation, and shipment from the factory to the farm (Lowe, 2005; Mina Boac et al., 2006). |
As a result, the pellets disintegrate, producing a high percentage of fines. These fines can negatively affect animal performance, as the mean geometric diameter is equal to or smaller than the particle size of the ground feed.
When studying the effect of thermal processing on the growth performance of growing and finishing pigs, Almeida et al. (2021) observed improvements in performance during the initial and growth phases when pigs were fed expanded rations, compared to those that received only ground feed.
The authors attribute the improved performance up to 128 days of age (growth) with processed diets compared to ground feed to starch gelatinization and protein denaturation (Skoch et al., 1983; O’Doherty et al., 2001; Rojas et al., 2016; Rojas and Stein, 2017).
Ginste and Schrijver (1998) found in their study that expanded diets resulted in a 5.5% higher feed consumption and a 7.8% higher growth rate in pigs. This improvement can be attributed to the inactivation of appetite-suppressing factors and the activation of the natural flavors of the ingredients (Armstrong, 1993; Peisker, 1994).
Final Considerations
Expansion is a process that can enhance feed utilization in swine by increasing the availability of nutrients in the diet and promoting higher feed consumption due to improved sensory characteristics. This contributes to reducing production costs in swine farming.
However, it is crucial that processing is done correctly to avoid over-processing or under-processing, which can lead to loss of nutritional quality due to issues such as the Maillard reaction or the formation of retrograded starch. These undesirable outcomes must be managed to ensure optimal feed quality and performance.
References available upon request