Objectives
- Determine the effect of different heat treatments of the digestibility of whole
flaxseed in rainbow trout.
2. Determine whether removal of mucilage by hot water extraction improves the
digestibility of mucilage in rainbow trout.
3. Determine the effects of feeding whole or low-mucilage flax seed on the growth
and feed efficiency of rainbow trout.
Project Description
Experiment 1 investigated the effect of different heat treatments on the nutrient digestibility of flaxseed in rainbow trout. Specifically, we compared micronization, autoclaving and extrusion as heat treatments to improve the digestibility of whole flaxseed to rainbow trout. Since extrusion of whole flax results in a significant leakage of oil, we co-extruded the flax with peas at a ratio of 1:1, flax:peas. The results of this experiment showed that all three heat treatments improved the dry matter and energy digestibility of flaxseed in rainbow trout. However, micronization had no effect on protein digestibility. Extrusion of whole flaxseed/whole pea was particularly beneficial in producing an ingredient with high fat digestibility and moderately high protein and energy digestibility. This trial demonstrated that extrusion of flaxseed results in a highly digestible feed ingredient that is rich in omega-3 fatty acids required by growing salmon and trout.
Experiment 2 investigated the digestibility of whole flaxseed and low mucilage flaxseed in rainbow trout. We used hot water extraction (HWE) to produce the low mucilage flaxseed. The results of this experiment indicate that hot water extraction of flaxseed was beneficial in reducing the viscosity of the HWE flax by 75% compared to whole flaxseed. This resulted in significant increases in protein, fat and energy digestibility of the HWE flaxseed. However, the flax was heat treated by autoclaving alone and so the overall digestibility of HWE flaxseed was only moderate. Mucilage extraction of flax should be combined with extrusion to maximize digestibility.
Experiment 3 was a growth trial in which we compared the growth performance and efficiency of rainbow trout fed whole flax seed or low mucilage flax seed (Hot Water Extracted-RWE). The dietary treatments were 1) Control diet containing no flax, 2) 6% whole flax seed, 3) 12% whole flaxseed, 4) 6% HWE flaxseed and 5) 12% HWE flaxseed. The fish were on trial for a period of 7 weeks and fish weights and feed intake were recorded weekly. The results of the trial indicated that mucilage is a significant antinutritional factor in flax. Inclusion rates of 6 or 12% of whole flaxseed reduced fish growth performance and feed efficiency. In contrast, HWE flax was readily consumed by rainbow trout at inclusion rates of up to 12% and fish had growth rates and feed efficiencies equal to the control diet.
Based on the results of these 3 experiments, our overall conclusions are:
1) Extrusion is required to maximize the digestibility of flaxseed to rainbow trout.
Coextrusion of flax with a high protein feed ingredient such as pea protein concentrate or canola protein concentrate appears to be the most desirable blend for the aquafeed industry. Such a product would be 1ich in omega-3 fatty acids and high in protein. We will investigate such products in future studies
2) Removal of mucilage by hot water extraction significantly increases the digestibility of flax to rainbow trout.
Low mucilage flax may be included in salmonid diets at inclusion rates of up to 12% with no reduction in feed intake, growth rate or feed efficiency.
3) Hot water extraction of flax to remove mucilage is not economical.
An alternative processing method must be developed to commercialize flax as an aquafeed ingredient. Dehulling appears to be such a method, and we have submitted a proposal to the Saskatchewan Flax Development Commission to develop dehulled flax coextruded with pea or canola protein concentrates as an aquafeed ingredient.
