Digestibility of feed ingredients and nutrients in artificial diets for fish

Appleford, Peter (1996) Digestibility of feed ingredients and nutrients in artificial diets for fish. PhD thesis, James Cook University of North Queensland.

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A knowledge of the digestibility of dietary ingredients and nutrients is essential to the formulation of nutritionally adequate, cost-effective artificial diets. Digestibility coefficients for fish have generally been determined using a single inclusion level and time point. The aim of the present study was to determine the effects of inclusion level and time on the digestibility of cellulose, tuna oil, corn starch, and soybean meal.

Incorporation of cellulose into the diet of the carnivorous Murray cod, Maccullochella peelii peelii, enhanced digestibility at 10% inclusion, while inhibiting digestion at higher inclusion. Conversely cellulose appeared digestible at a nutritionally significant level for the omnivorous common carp, Cyprinus carpio. Decreased digestibility at higher inclusion levels suggesting a saturable mechanism. Antibiotics failed to inhibit cellulose digestibility, indicating a lack of involvement of intestinal micro-flora, however microbiological analysis suggested the antibiotic treatment employed did not effectively eliminate gut bacteria. Cellulose inclusion did not consistently affect dietary protein or ash digestibility, however lipid digestibility decreased linearly with the level of cellulose incorporation. Antibiotics did not affect dietary nutrient digestibility.

The digestibility of tuna oil at 10% and 15% inclusion indicated reduced digestibility with inclusion. However daily faecal analysis showed a continuing adaptation to the high lipid diet, with digestibility of tuna oil at the later time points similar at both inclusion levels. Tuna oil inclusion did not affect dietary protein or ash digestibility.

Raw corn starch digestibility for common carp was high, greater than 79%, at all inclusion levels. At restricted feeding starch digestibility was found to increase with inclusion up to 40%. At 20% inclusion digestibility of energy from starch reflected dry matter digestibility of the ingredient. Incorporation of 20% starch decreased protein digestibility, however this was not of a nutritionally significant level.

A negative effect of inclusion on the ground solvent-extracted soybean (SBM) digestibility was found, digestibility decreasing at greater than 20% inclusion. There was also a trend for protein digestibility to decrease with inclusion, however this was not significant. Dry matter, protein and energy digestibility for SBM by common carp was not affected by grinding, sifting or grinding the sifted middlings. Ground SBM inclusion did not affect dietary crude lipid digestibility. Soybean oil digestibility was extremely variable and was not affected by inclusion level.

Throughout the study digestibility varied with time, showing both adaptation over time and a cyclic daily variation. Analysis of daily faecal samples exemplified the degree to which these factors affect digestibility measurement.

Where measured, ash was significantly digestible, indicating ash should not be used as an endogenous digestibility marker.

The above results suggest digestibility varies with both ingredient inclusion level and time. Dietary ingredients may also adversely affect the digestibility of other dietary nutrients. When determining the digestibility of dietary ingredients, it would appear necessary to determine digestibility coefficients over the range of inclusion to be used and over time. Any adverse effects of the dietary ingredient on the digestibility of other dietary components also needs to be considered.

Item ID: 33761
Item Type: Thesis (PhD)
Keywords: diet; digestibility; digestion; feeding; feeds; fish; fishes; Murray cod; nutrition
Date Deposited: 07 Jul 2014 23:36
FoR Codes: 06 BIOLOGICAL SCIENCES > 0606 Physiology > 060603 Animal Physiology Systems @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 33%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960807 Fresh, Ground and Surface Water Flora, Fauna and Biodiversity @ 33%
83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830102 Aquaculture Fin Fish (excl. Tuna) @ 34%
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