Effect of DHA supplementation on digestible starch utilization by rainbow trout.
Rainbow trout has a limited ability to utilize digestible carbohydrates efficiently. Trout feeds generally contain high levels of DHA, a fatty acid known to inhibit a number of glycolytic and lipogenic enzymes in animals. A study was conducted to determine whether carbohydrate utilization by rainbow trout might be affected by dietary DHA level. Two low-carbohydrate (<4 % digestible carbohydrate) basal diets were formulated to contain 1 (adequate) or 4 (excess) g/100 g DHA diet respectively. The two basal diets were diluted with increasing levels of digestible starch (0 %, 10 %, 20 % and 30 %, respectively) to produce eight diets. These diets were fed to fish for 12 weeks at 15 degrees C according to a pair-fed protocol that consisted of feeding the same amount of basal diet but different amounts of starch. Live weight, N and lipid gains, hepatic glycogen and plasma glucose values significantly increased, whereas feed efficiency (gain:feed) significantly decreased, with increasing starch intake (P<0.05). The retention efficiency of N (N gain/digestible N intake) improved with starch supplementation but was not affected by DHA level (P>0.05). Starch increased the activity of glucokinase, pyruvate kinase, glucose 6-phosphate dehydrogenase and fatty acid synthase (P<0.05) but did not affect hexokinase and malic enzyme activity. DHA had no effect on growth but increased plasma glucose and reduced carcass lipid and liver glycogen contents (P<0.05). Glycolytic and lipogenic enzymes were not affected by DHA level, except for pyruvate kinase, which was reduced by increasing DHA level. These results suggest only a marginal effect of dietary DHA on the ability of fish to utilize carbohydrate.
Tapia-Salazar
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Department of Animal and Poultry Science, University of Guelph, Guelph, ON, N1G2W1, Canada.
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D000821:Animal Feed; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D001835:Body Weight / Q000502:physiology; D004040:Dietary Carbohydrates / Q000493:pharmacokinetics*; D004041:Dietary Fats / Q000032:analysis; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology; D004281:Docosahexaenoic Acids / Q000008:administration & dosage / Q000494:pharmacology*; D005227:Fatty Acids / Q000032:analysis; D006003:Glycogen / Q000032:analysis; D008099:Liver / Q000737:chemistry / Q000201:enzymology; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D013213:Starch / Q000493:pharmacokinetics*
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005227:Fatty Acids; D004281:Docosahexaenoic Acids; D013213:Starch; D006003:Glycogen