Sodium Alginate Addition Improves Water Stability and Utilization of Extrudated Feed for Farmed Saltwater Crocodiles (C. porosus)

Abstract Text:

Saltwater crocodile (C. porosus) farming in Papua New Guinea is an emerging industry that supplies high quality raw skins for fashion industries worldwide. Extrudated animal by-product feed (non-heat treated feed forced through a die at low pressure) is used to get a consistent high quality feed, however, this feed disintegrates quickly in water which leads to loss of nutrients, inefficient feed conversion ratio, and water contamination. We evaluated Na alginate as a binding agent to improve feed stability in water and determined its effect on nutrient availability in a digestibility trial. A 24-h in vitro water solubility test of exudated chicken by-product-based diets (35% minced chicken carcasses, 15% chicken blood, 5% poultry offal meal, 5% pulped eggs, 15% wheat millrun, and 25% supplement, as-fed basis) with and without 1.5% Na alginate and 1.9% CaCO₃ added showed the inclusion of Na alginate improved the dry matter retention in feed by 12.6-times (P < 0.05). These diets were then compared in vivo in a digestibility trial. Ten juvenile crocodiles (2.2-2.4 years of age, 1.2-1.9 kg BW) were chosen from farm raised stocks and fed exudated chicken by-product-based diets with and without 1.5% sodium alginate and 1.9% CaCO₃ added. Animals were fed 2% BW for 12 d, with feces collected the last 5 d. Animals were then slaughtered and digesta sampled from the ileum. Acid insoluble ash was used as an internal marker. There were no differences in any amino acid, N (65.0 vs 55.8%, SE = 12.2%), and organic matter (46.8 vs 39.6%, SE = 12.8%) digestibility at the ileum between diets with and without alginate, respectively. However, fecal digestibility of organic matter (69.8 vs 39.2% SE = 9.1%) and energy (72.2 vs 44.4%, SE = 8.3%) were greater in alginate containing diets (P < 0.05). This shows that alginate addition does not have deleterious effects on digestion in crocodiles, and because it improves feed stability in water, should greatly enhance nutrient uptake and feed efficiency. Results will be used to formulate diets with increased feed utilisation and decreased feed wastage, with the ultimate goal of increasing economic return to Papua New Guinea whilst decreasing effluent discharge and pollution of the ecosystem.

Keywords: Saltwater crocodile, ileal digestibility, sodium alginate