Husdyr- og akvakulturvitenskap
Ståle Refstie - abstract fra doktorgradsavhandling
Ane Gro Siri Skjelfjord
Abstract fra avhandlingen
Evaluating soybean meal as a fish meal substitute in feeds for Atlantic salmon and rainbow trout / Vurdering av soyamjøl for delvis erstatning av fiskemjøl i fôr til laks og regnbueaure
Defatted and toasted (steam-cooked) soybean meals are among the most interesting protein feed ingredients that may partially substitute expensive fish meals in least-cost formulated feeds for salmonids. However, this ingredient also contains numerous indigestible and/or antinutritional components. Hence, this study aimed to quantify dietary effects on important production traits in Atlantic salmon and rainbow trout when partially substituting LT-fish meal by defatted and toasted soybean meal in the diet. The studied traits included appetite, macronutrient absorption, growth rate, feed utilization, budgeting of macronutrient utilisation, body composition, and flesh quality at slaughter. The flesh quality study tested dietary effects of full-fat soy, as dietary lipid sources influence the organoleptic properties of salmonid flesh more than dietary protein sources.
Partial substitution of fish meal to include 40% soybean meal in the diet temporarily reduced the qualitative preference for the diet by rainbow trout adapted to a fish meal based feed. This was not seen in Atlantic salmon adapted to a fish meal based feed when including 34% soybean meal in the diet. Atlantic salmon instead responded to the soybean meal diet by temporarily reduced appetite and digestive disturbances. Both species developed enteritis in the distal intestine in response to dietary soybean meal, but this condition was less pronounced in rainbow trout. Generally, Atlantic salmon utilised the dietary protein and energy more efficiently for growth than rainbow trout, whereas rainbow trout suffered less severe digestive disturbances than Atlantic salmon when fed soybean meal. Including 15 to 48% soybean meal in the diet reduced the lipid digestibility by Atlantic salmon, and this reduction was inversely related to the level of soybean meal in the diet. It seemed to be caused by soluble soy carbohydrates and/or antinutritional factors that may be extracted with alcohol along with the carbohydrates. Atlantic salmon grew well on a diet with 18% soybean meal, but growth was compromised with a 30% soybean meal diet. Rainbow trout grew well on a diet with 30% soybean meal, and appeared able to adapt to even higher dietary soybean meal levels. Long-term feeding of diets with 7 to 9% full-fat soy did not affect flesh quality of slaughtered Atlantic salmon.
In consequence, this calls for cautious use of soybean meals in diets both for Atlantic salmon and rainbow trout, but in particular for Atlantic salmon. The study also illustrates the importance of budgeting nutrient utilisation when evaluating feed ingredients for salmonids in order to reveal how dietary ingredients interact to affect the overall absorption and utilisation of nutrients.
Key words: Feedstuff-evaluation; Fish meal-soybean meal; Feed consumption-adaptation-palatability; Growth-digestibility-feed conversion-retention; Dietary fibre-viscosity; Soybean meal-induced enteritis; Lipid deposition-slaughter quality; Atlantic salmon (Salmo salar)-rainbow trout (Oncorhynchus mykiss)
Oppdatert: 05.01.09Utskriftsvennlig versjon
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