Abstract
In the present study, two salmon feeds with different disintegration stabilities were produced by impacting extruder viscous heat dissipation with the use of different lipid levels in the feed mix. The feeds were then dried and coated to similar final lipid levels (30-31%) and nutritional composition. Both feeds were produced as 4 and 6-mm pellets. Feeds extruded with 20% lipid had a lower disintegration stability compared with those with 8% lipid. The feeds were used in two feeding studies using Atlantic salmon (Experiments 1 and 2) and an in vitro gastric study (Experiment 3). In Experiment 1, salmon postsmolts (370 g starting weight) fed the 4-mm pellets showed the fastest gastrointestinal (GI) passage rate when fed feeds with a lower disintegration stability. This was due to a faster transport of content from the stomach to the gut at 30 min and 1.5 h after a meal, and faster passage through the distal gut 9–24 h after a meal. The 6-mm pellets were used in a 100-day feeding study (Experiment 2) in which salmon fed high and low disintegration stability feeds grew from 572 to 1542 and 1604 g, respectively. There was a higher total feed intake in salmon fed diets with lower disintegration stability, but only tendencies towards higher growth and final body weight compared with salmon fed diets with a higher disintegration stability. The in vitro gastric experiment showed that pellets with a lower disintegration stability required a larger supply of stomach acid to maintain a stable pH of 4.5, which also gave a lower content viscosity. The in vitro study also showed an increased release of water-soluble components from these pellets and hydrolysis of larger peptides increased the pool of intermediate-sized peptides (4–6 kDa) available for easy transportation, hydrolyzation, and absorption in the proximal intestine. Although lower pellet disintegration stability increases feed intake. The GI passage rate combined with an increased GI filling can affect the ability to hydrolyze and absorb nutrients. This may explain why an increased feed intake did not result in increased growth in Experiment 2, despite observing no significant differences in nutrient digestibility or feed conversion ratio. Our results highlight the importance of the quality of extruded fish feed.
Highlights
Key factors for shorter production time and reduced costs in the commercial production of Atlantic salmon (Salmo salar) include high feed intake, efficient feed utilization, and high growth rates (Einen et al, 1995)
It is an important organ for short-term storage while food is effectively processed via disintegration and pre digestion to a fluidized mass that is transferred to the proximal part of the intestinal tract, determining the gastrointestinal (GI) passage rate, nutrient digestibility, and feed intake (Grove et al, 1978; Soengas, 2014)
The present study demonstrates that increased feed intake does not necessarily result in a significantly higher growth rate
Summary
Key factors for shorter production time and reduced costs in the commercial production of Atlantic salmon (Salmo salar) include high feed intake, efficient feed utilization, and high growth rates (Einen et al, 1995). The stomach has several functions that are related to both the utilization and intake of feed It is an important organ for short-term storage while food is effectively processed via disintegration and pre digestion to a fluidized mass (chyme/digesta) that is transferred to the proximal part of the intestinal tract, determining the gastrointestinal (GI) passage rate, nutrient digestibility, and feed intake (Grove et al, 1978; Soengas, 2014). Feeds are hydrated in a mixture of acid (HCl) and gastric enzymes (mainly pepsin; Koelz, 1992; Einarsson et al, 1996) that disintegrates the surface of the food items and releases smaller particles and water-soluble components into the liquid phase that are transferred to the in testine (Andersen and Beyer, 2005). Feeds comprising partly hy drolyzed nutrients and/or those with a low disintegration stability may be beneficial for faster emptying of the stomach and ensuring high feed intake
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