|Abstract:||Omega-3 polyunsaturated fatty acids (w3-PUFA), including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are critical nutrients in feline diets. These nutrients are utilized as a key source of energy, in the transport of fat-soluble vitamins, in the formation of eicosanoids in inflammatory responses, and in the development of neural, retinal, and auditory functions. These w3-PUFA most commonly are added to feline diets through marine sources, mainly fish. Sustainability has become a concern in recent years. Algae can be a sustainable alternative for dietary supplementation of w3-PUFA; however, there is limited information on the safety and bioavailability of w3-PUFA from algal sources in feline diets. Therefore, the objective of this study was to determine the effects of dietary supplementation of algal-DHA (aDHA) on plasma fatty acid profile, blood coagulation parameters, and apparent total tract nutrient digestibility (ATTD) by adult cats. Three diets were formulated to contain 10% poultry fat alone (control; CT) or 8% poultry fat with a 2% inclusion of fish oil (FO) or a 2% inclusion of aDHA. All diets met or exceeded AAFCO nutrient profiles for adult cats. Thirty female and male adult cats (mean age: 1.8 ± 0.03 yr, mean BW: 4.5 ± 0.8 kg) were used in a completely randomized design and fed assigned diets for 90 d. Fasted blood samples were collected on 0, 30, 60, and 90 d and analyzed for serum metabolites, complete blood count, coagulation parameters, and plasma and red blood cell fatty acid profiles. A 4-d total fecal collection was performed at the end of the experimental period for determination of ATTD of macronutrients and fecal score. All diets were well-accepted by the cats and there were no differences (P > 0.05) in food intake among treatments. Similarly, fecal output and scores did not differ (P > 0.05) among dietary treatments, with scores being in the ideal range (score 2-3). All diets were highly digestible, and ATTD of dry matter, organic matter, crude protein, fat, and fiber did not differ (P > 0.05) among diets. Dietary supplementation of fish oil or aDHA did not affect (P > 0.05) plasma prothrombin time (PT), partial thromboplastin time (PTT), or fibrinogen parameters. All cats remained healthy throughout the study. Serum triglyceride concentrations were within reference range, but were higher (P<0.05) for the CT diet when compared to cats fed either aDHA or FO diets. Fecal short-chain fatty acids, acetate, and propionate were higher (P < 0.05) for the aDHA treatment than for the CT treatment with no significant difference for either treatment compared to FO (P > 0.05). Fecal phenols and indoles and phenols alone were higher (P > 0.05) for the cats fed the aDHA treatment compared to both those fed the CT and FO treatments. Results indicate a 2% inclusion of DHA-enriched algal meal in a nutritionally complete adult cat food was a safe, bioavailable, and a sustainable alternative to FO in feline diets.