Pea and canola meal products with thin distillers' solubles in diets for rainbow trout (Oncorhynchus mykiss)
Thiessen, Debra Dora Lee
The purpose of this project was to determine the suitability of pea and canola products, and of thin distillers' solubles, for use in salmonid diets with the ultimate aim of enhancing market opportunity for these agricultural crops and byproducts produced in western Canada. Four experiments were conducted with rainbow trout to evaluate the palatability, digestibility and nutritional value of pea and canola products. The ability of thin distillers' solubles to increase feeding activity, and the effect this product has on nutrient and dry matter digestibility of pea products, was also evaluated. Experiments one and two were conducted with the objective of comparing feed consumption, time to satiation and feeding aggressiveness in fish fed four diets containing canola meal or air-classified pea protein, with or without the presence of a palatability enhancer (Finnstim™). Feed consumption of a diet containing 15% canola meal was equal to that of a commercially available trout ration (P ≤ 0.05). Feed consumption of a diet containing 30% air-classified pea protein, although being lower than the commercial ration (P ≤ 0.05), did not indicate severe palatability problems. It was concluded that these two ingredients offer potential as alternative plant protein sources for feeding rainbow trout. Feed consumption of neither plant protein source was increased with supplementation of a commercial palatability enhancer. However, feeding response was significantly increased (P ≤ 0.05) with supplementation of thin distillers' solubles at a level ≥ 3.3%; of the diet. Experiment three determined the effects that various milling and heat treatments had on nutrient, dry matter and energy digestibility of four pea ingredients as follows: autoclaved air-classified pea protein, raw/whole peas, raw/dehulled peas and extruded/dehulled peas. Digestibility of the protein component was uniformly high for all pea ingredients (apparent digestibility coefficient (ADC) of 90.0-94.6%), regardless of the processing treatment, and compared favourably to protein digestibility values from other plant sources. Heat treatments achieved by autoclaving or extrusion greatly increased starch digestibility by 41-75% (P ≤ 0.05), which consequently increased energy and dry matter digestibility of whole and dehulled peas. Autoclaved air-classified pea protein had superior protein (ADC of 94.6%), energy (ADC of 87%) and dry matter (ADC of 84%) digestibility that compared favourably with other plant sources currently utilized in aquafeeds. Thin distillers' solubles was a highly digestible ingredient and supplementation with this product did not adversely affect digestibility values of the various pea ingredients. Experiment four compared the growth performance of rainbow trout fed diets containing soybean meal, dehulled peas, air-classified pea protein or canola meal fines as the primary plant ingredient in the diet, and evaluated the effectiveness of thin distillers' solubles as a feed enhancing compound for rainbow trout over a 12 week period. Feed intake, weight gain, feed conversion, specific growth rate, protein efficiency ratio, hepatosomatic index and dressout percentage were similar for the four plant protein sources (P ≤ 0.05). It was concluded that dehulled peas, air-classified pea protein and canola meal fines are suitable ingredients for use in trout diet formulation. Addition of thin distillers' solubles, while increasing feed intake in the short term, did not increase feed intake (P ≤ 0.05) ofpea and canola diets over the 12 week trial period. It can be concluded that further processing of peas and canola meal is of benefit in producing palatable, nutritious ingredients suitable for rainbow trout diet formulation. Peas, regardless of processing treatment, were a palatable ingredient. However, digestibility of the nutrient and energy fraction of peas varied with processing treatment. Air classification of dehulled peas produced a highly desirable pea ingredient with a concentrated protein, low starch content which resulted in superior digestibility relative to whole, dehulled or extruded peas. Similarly, sieving of conventional canola meal produced a palatable, high protein ingredient. Thin distillers' solubles were not effective as a palatability enhancer over a long-term period. The failure of this product to increase feed intake may be attributed to the destruction of amino acids during thermal processing or due to a decrease in gustatory stimulation with time. In conclusion, the overall results of these experiments show that there is great opportunity for utilization of pea and canola products in aquafeeds provided adequate processing treatments are used to concentrate the protein constituents and to remove components which inhibit digestion, absorption and utilization of these alternative protein sources by salmonid species.