A comparison of two fecal collection methods for protein and amino acid digestibility coefficients for menhaden fish meal and two grades of pultry-by-product meals in market-size sunshine bass (Morone chrysops X M. saxatilis)

Authors: Rawles, Steven - Steve; THOMPSON, KENNETH - KENTUCKY STATE UNIVERSITY; METTS, LINDA - KENTUCKY STATE UNIVERSITY; GANNAM, ANN - USFWS; TWIBELL, RONALD - USFWS; BRADY, YOLANDA - AUBURN UNIVERSITY; WEBSTER, CARL - KENTUCKY STATE UNIVERSITY

Submitted to: Aquaculture Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2008
Publication Date: 2/25/2009
Citation: Rawles, S.D., Thompson, K.R., Metts, L.S., Gannam, A.L., Twibell, R.G., Brady, Y.J., Webster, C.D. 2009. A comparison of two fecal collection methods for protein and amino acid digestibility coefficients for menhaden fish meal and two grades of pultry-by-product meals in market-size sunshine bass (Morone chrysops X M. saxatilis). Aquaculture Nutrition. 16:81-90.

Interpretive Summary: Sunshine hybrid striped bass is an expanding U.S. aquaculture industry. In order to manufacture fish feed, feed mills need digestibility coefficients that have been determined for nutrients in a variety of ingredients. Digestibility measured in other species of fish is not the same as digestibility measured in hybrid striped bass. The size of fish also affects how well nutrients in different ingredients are digested. Therefore, digestibility in stocker fish is different than that of fish nearing market size. Arkansas produces a great deal of poultry by products that show promise as ingredients in fish feed. Finding suitable replacements for fish meal are a priority of the processing and fish industries. We determined the digestibility of protein and amino acids in menhaden fish meal, pet food grade poultry by-product and feed-grade poultry by-product for market-size (1 lb) sunshine hybrid striped bass. We also used two different methods, passive netting and manual stripping, to measure digestibility. The passive netting method was chosen because successful use of this method would allow measuring digestibility without handling, disturbing, or stressing the fish. The manual stripping method was used because this is the standard method used for this kind of research. The test diets were manufactured under commercial conditions to mimic feed used in the industry. Market size fish were fed their respective test diets containing one of the above ingredients of interest for 6 days before digestibility was measured. Protein in all three ingredients was well digested by market size hybrid striped bass bass. Protein digestibility was significantly greater when determined by manual stripping than by passive netting. The digestibility of protein ranged from a low of 80% (feed-grade poultry by-product) to a high of 99% (menhaden fish meal) in the manual stripping method and from a low of 51% (feed-grade poultry by-product) to a high of 87% (pet food grade poultry by-product) in the passive netting method. The digestibilities of protein in fish meal and in pet food grade poultry by-product were not significantly different regardless of which method was used, but the digestibility of protein in feed-grade poultry by-product was less than that of pet-food grade poultry by-product. There were no significant differences in the digestibilities of fourteen amino acids in the test ingredients regardless of the method used for determining digestibility. However, digestibilities of amino acids measured in the passive netting method were much more variable than those measured in the manual stripping method. Based on these results, the passive netting method is not recommended for determining the digestibility of nutrients in feed ingredients for market-size sunshine hybrid striped bass. However, digestibility coefficients measured by the manual striping method will be useful for formulating more efficient and economical diets for sunshine bass nearing market size.

Technical Abstract: Apparent digestibility and availability coefficients for protein and amino acids in menhaden fish meal (MEN), pet-food grade (PBM-pet,) and feed-grade poultry by-product meal (PBM-feed) were determined for market-size (500 g) sunshine bass using passive netting or manual stripping of feces. A reference diet resembling a commercial feed was formulated to meet or exceed all known nutritional requirements of hybrid striped bass. Test diets were formulated to contain a 70:30 mixture of reference diet to test ingredient with chromic oxide (1%) serving as the inert marker. Diets were extruded under commercial conditions and the reference diet was fed for two weeks in order to acclimate fish to experimental conditions. Each diet x method combination was randomly assigned to triplicate tanks containing 30 fish each and fish were fed their respective diet twice daily to apparent satiation for 6 days prior to fecal collections. In general, protein in all three test diets was well digested by market size sunshine bass. There was no significant interaction (P = 0.29) between diet and fecal collection method in the protein digestibility data. Protein digestibility ranged from a low of 51% (PBM-feed) to a high of 87% (PBM-pet) in the net method, and from a low of 80% (PBM-feed) to a high of 99% (MEN) in the strip method. Protein digestibilities in MEN (89%) and PBM-pet (86%) were not significantly different, but were greater (P < 0.10) than that of PBM-feed (65 %), regardless of method. Likewise, protein digestibility was significantly greater in samples obtained by manual stripping (87%) than in samples obtained by passive netting (73%), regardless of test diet. Significant differences among diets or methods were generally lacking in the availabilities of fourteen amino acids measured in the test diets. Coefficients of amino acid availabilities were highly variable among samples from either method; however, availabilities measured in netted fecal samples were much more variable than those in stripped fecal samples. In addition, the availabilities of amino acids in PBM feed appeared more variable than those determined in MEN and PBM-pet for fecal samples obtained in the net method. Data from the present study suggest that marker, rather than nutrient, leaching in the net method may have been prevalent. Based upon the conditions of the present study, net collection of fecal matter can not be recommended for determining the digestibility of nutrients in feed ingredients for market-size sunshine bass. Digestibility coefficients obtained by the strip method will be useful for formulating more efficient and economical diets for larger sunshine bass. However, changes in experimental conditions, such as increasing water flow and/or more frequent collection of fecal samples in the collection nets, may reduce variability and increase the accuracy of ADCs obtained by this method.