Optimal Incorporation Level of Dietary Alternative Phosphate (MgHPO4) and Requirement for Phosphorus in Juvenile Far Eastern Catfish (Silurus asotus)

Dietary phosphorus requirement of silver CARP (Hypophthalmichthys molitrix) fingerlings

The aim of this study was to determine the optimal dietary phosphorus (P) requirement and its effects on growth performance, body composition, mineralization and alkaline phosphate (ALP) activity in silver carp (Hypophthalmichthys molitrix). A total of 360 fish with an average initial weight of 7.0 ± 0.15 g were divided into 18 tanks (70 L capacity each) with a stocking density of 20 fish per tank in triplicate. The fish were fed diets containing six levels of P (3.3, 4.4, 5.5, 6.5, 7.5 and 8.6 g/kg) up to satiation for 90 days twice daily at 09:00 and 16:00. The results showed that fish fed diets containing 6.5 and 7.5 g/kg dietary P had significantly higher (p < 0.05) growth performance in terms of final weight gain, average weight gain (AWG), weight gain% (WG%), protein efficiency ratio (PER) and specific growth rate (SGR) than fish fed other diets. The best value of the feed conversion ratio (FCR) was observed in fish fed the 6.5 g/kg P diet, which was not significantly different from the 7.5 g/kg P diet. Increasing P supplementation above 6.5 g/kg significantly reduced (p < 0.05) the feed intake of silver carp. Whole-body composition analysis indicated that increasing P levels resulted in a decrease (p < 0.05) in crude fat (CF) and an increase (p < 0.05) in crude ash (CA) content, while crude protein (CP) and moisture content remained unaffected (p > 0.05). Fish fed diets containing ≥6.5 g/kg P had significantly higher (p < 0.05) Ca content in the whole body, bones and scales compared to those fed diets containing ≤5.5 g/kg P. A similar trend was observed for P and Mg contents in the whole body, bones and scales. The Zn content tended to decrease (p < 0.05) with increasing P supplementation in the whole body and bones, but fish fed diets containing ≥6.5 g/kg P had significantly higher (p < 0.05) Zn content compared to fish fed diets containing ≤5.5 g/kg P. The Ca/P ratio was significantly affected by P supplementation. Fish fed diets containing ≥6.5 g/kg P had significantly higher (p < 0.05) Ca and P contents in the serum than fish fed other diets. ALP activity increased (p < 0.05) with increasing P levels up to 6.5 g/kg P and decreased (p < 0.05) thereafter. In conclusion, supplementing P up to 6.35 g/kg is recommended for the optimal growth of silver carp.

Influence of Dietary Phosphorus on the Growth, Feed Utilization, Proximate Composition, Intestinal Enzymes, and Oxidation Resistance of Sea Cucumber Apostichopus japonicus

Six experimental diets (crude protein 12.58%, crude fat 1.93%, and total energy 10.72 kJ/kg) containing 0.24%, 0.37%, 0.51%, 0.62%, 0.77%, and 0.89% phosphorus were formulated to evaluate dietary phosphorus requirement for sea cucumber Apostichopus japonicus. The feeding trial was conducted in 18 fiberglass tanks (220 L) for 63 days. Each diet was randomly assigned to triplicate tanks of 50 sea cucumbers (9.99 g) and fed once daily. With the increase of dietary phosphorus level, weight gain (WG), specific growth rate (SGR), daily feed intake (DFI), feces production ratio, the activities of amylase, alkaline phosphatase, phosphofructokinase, succinate dehydrogenase, and glutathione peroxidase as well as the contents of glutathione and glutathione oxidized significantly increased and then decreased afterwards (P < 0.05). A. japonicus fed diet with 0.63%, 0.63%, and 0.55% dietary phosphorus was estimated to yield the highest WG (11.39 g), SGR (1.09%/d), and DFI (2.55%/d) according to the quadratic regression analysis of WG, SGR, and DFI against dietary phosphorus level, respectively. The apparent digestibility of dry material and energy followed an opposite tendency. Feed efficiency, the contents of whole-body phosphorus, initially increased and then plateaued, fitting piecewise-linear models with breakpoint at 0.57% and 0.55% dietary phosphorus. Daily phosphorus intake, pyruvate kinase activity, and the ratio of glutathione and glutathione oxidized increased (P < 0.05) but the apparent digestibility of phosphorus, the activities of alkaline protease, aspartate transaminase, and phosphoenolpyruvate carboxykinase decreased (P < 0.05), responding to the increasing dietary phosphorus. Considering the present results, the optimal dietary phosphorus for A. japonicus is 0.57-0.63%.

In Vivo Toxicity and In Vitro Solubility Assessment of Pre-Treated Struvite as A Potential Alternative Phosphorus Source in Animal Feed

Apart from using as fertilizer for plants, the application of struvite may be expanded to animal feed industries through proper pre-treatment. This study aimed to investigate the safety and efficacy of using pre-treated struvite (microwave irradiated struvite (MS) and incinerated struvite (IS)) in animal feeds. For safety assessment, an in vivo toxicity experiment using thirty female Sprague Dawley rats (average body weight (BW) of 200 ± 10 g) was conducted. The rats were randomly divided into five groups, including a control. Based on the BW, MS and IS were applied daily by oral administration with 1 and 10 mg kg^-1-BW (MS1 and MS10; IS1 and IS10) using dimethyl sulfoxide (DMSO) as a vehicle. A series of jar tests were conducted for four hours to check the solubility of the MS and IS at different pH (pH 2, 4, and 5) and compared to a commercial P source (monocalcium phosphate, MCP, control). The toxicity experiment results showed no significant differences among the treatments in BW and organ (liver, kidney, heart, and lung) weight of rats (p > 0.05). There were no adverse effects on blood parameters and the histopathological examination showed no inflammation in the organ tissues in MS and IS treated groups compared to the control. In an in vitro solubility test, no significant difference was observed in ortho-phosphate (O-P) solubility from the MCP and MS at pH 2 and 4 (p > 0.05), while O-P solubility from MS at pH 5 to 7 was higher than MCP and found to be significantly different (p < 0.05). O-P solubility from IS was the lowest among the treatments and significantly different from MCP and MS in all the experiments (p < 0.05). The results of this study not only suggest that the struvite pre-treated as MS could be a potential alternative source of P in animal feed but also motivate further studies with more stringent designs to better examine the potential of struvite application in diverse fields.

Nutrient Leaching Loss of Pre-Treated Struvite and Its Application in Sudan Grass Cultivation as an Eco-Friendly and Sustainable Fertilizer Source

Struvite recovered from waste streams is considered as a sustainable alternative to commercial phosphate (P) fertilizers manufactured from P rock. In this study, struvite was recovered from swine wastewater and pre-treated as air-dried material (AM), microwave irradiated material (MM), oven-dried material (OM), and incinerated material (IM) to reduce the moisture content. Based on their solubility and crystalline nature, AM and IM were selected for further experiments. The nutrient leaching loss and fertilizing value of AM and IM were evaluated in comparison to commercial fused superphosphate (FSP) fertilizer. Soil columns were used to quantify ortho-phosphate (O-P) and ammonium nitrogen (NH4-N) leaching in soil from the test materials. Among the test materials, the average leaching rate of O-P for FSP and AM was significantly different from the control and IM (p < 0.05). The average leaching rate of NH4-N among the test materials did not show any significant difference (p > 0.05). Sudan grass growth was examined with standard (urea supplemented) and high (20x, without urea) application of test materials in pot and soil box trials, respectively, to study the fertilizing value AM and IM. There were no significant differences among the test materials, except for the control, in terms of growth rate and fresh and dry matter yield in the pot trials (p > 0.05). When AM, IM, and FSP were applied in increasing amounts (20x) without urea supplement, Sudan grass growth was 50% lower in IM and was found to be significantly different from AM and FSP (p < 0.05). The results suggest that struvite pre-treated as AM could be an effective sustainable and eco-friendly alternative to commercial P fertilizers and thus helps to ensure agricultural sustainability.