An evaluation of co-extruded poultry silage and culled jewel sweet potatoes as a feed ingredient for hybrid Tilapia ( Oreochromis niloticus× O. mossambicus)

Abstract

Two experiments were conducted with hybrid tilapia to evaluate a meal made by extrusion co-processing culled sweet potatoes and poultry mortality silage (ESPFP). In both experiments, dried, cull sweet potatoes and fermented whole turkey carcasses (60:40 ratio, w/w wet basis) were co-extruded, dried, and hammer-milled to make the ESPFP test ingredient. The resulting ESPFP meal was included at 0%, 11%, 22%, and 33% by weight in isocaloric, isonitrogenous pelleted diets. In an 87-day growth trial, no significant differences were found in the growth parameters or carcass (market) yields among the treatment groups. Tank water quality parameters were also unaffected by inclusion of the experimental ingredient. A consumer panel found no significant differences in the sensory indices (aroma, flavor, and texture) of the fillets from fish fed with the graded levels of ESPFP in the diet versus those from fish fed the control diet. The digestibility of the diets containing the ESPFP meal was evaluated in a second trial. The apparent dry matter (DM), gross energy (GE), and crude protein (CP) digestibility coefficients were reduced linearly with increasing levels of the ESPFP meal in the diets ( P<0.019). However, the level of inclusion of the ESPFP meal had no effect on the apparent organic matter (OM) digestibility coefficient values among the diets. Acid detergent fiber (ADF) and acid detergent insoluble nitrogen (ADIN) increased linearly ( P<0.001) with increasing levels of ESPFP in the diets, indicating significant heat damage had occurred during manufacture of the test ingredient. The indigestible Maillard polymers formed during extrusion co-processing and drying of these two ingredients accounted for 93% of the reduction in protein digestibility in the diets and were a contributing factor to the reductions in DM and GE digestibility. Extrusion co-processing of culled sweet potatoes and poultry mortality silage produces an acceptable feed ingredient for hybrid tilapia that can be included at up to 33% of the diet without adversely affecting growth, market yield, sensory indices, or water quality as compared to a standard tilapia diet.