| Abstract | The present study is the second in a series of projects designed to evaluate the nutritional value of S-AMDD for animal feed applications. The main objective was to generate novel digestibility data of whole-cell and lipid-extracted S-AMDD for both ruminant and monogastric animals including ruminal organic matter digestibility (OMD), apparent metabolizable energy (aME) content, methane (CH4) production, dilute pepsin digestibility (DPD) and two-phase gastric/pancreatic digestibility of protein (GPDProtein) and energy (GPDEnergy). Simulated ruminal fermentations using lactating dairy cattle as rumen fluid donors indicate that both whole-cell and lipid-extracted S-AMDD have excellent potential for use in ruminant animal feeds. Dietary inclusion of whole-cell S-AMDD at 50% forage protein replacement (equivalent to 20% of the total diet) or lipid-extracted S-AMDD at 100% forage protein replacement (equivalent to 32% of the total diet) did not significantly affect OMD or aME content of the control diet. However, OMD was marginally comprised with 100% forage protein replacement with whole-cell S-AMDD (equivalent to 40% of the total diet) relative to the 25 and 50% replacement levels, although not significantly different from the control diet. Diets containing lipid-extracted S-AMDD significantly reduced CH4 production by approximately 50% compared to the control diet (47% reduction) and those containing whole-cell S-AMDD (51% reduction). Since OMD and aME content of diets containing lipid-extracted S-AMDD were unaffected relative to the control diet and whole-cell S-AMDD-containing diets, it seems clear that lipid-extracted S-AMDD contains anti-methanogenic ‘non-fatty acid’ substances that have the ability to suppress rumen methanogenic bacteria without disturbing ruminal digestion. This area warrants further exploration in vivo, especially considering the large volume of algal feed that could be produced without occupying significant land resources. In vitro monogastric digestibility using porcine enzymes indicates that lipid-extracted S-AMDD has potential for use in monogastric animal feeds. Protein and energy digestibility of this product were moderately high (75-84% and 70%, respectively); which resulted in relatively high contents of DP (30%) and DE (14 MJ kg-1). On the other hand, the digestibility of whole-cell S-AMDD was low at 52-61% and 50%, respectively resulting in lower levels of DP (15%) and DE (12 MJ kg-1). Despite the encouraging results for lipid-extracted S-AMDD, the digestibility (particularly of energy) remains marginal for monogastric animals and requires improvement through additional cost-effective cell rupture technologies or the production algal protein concentrates. |
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