Effects of spray-dried plasma on nutrient digestibility, fecal metabolites, microbiota, and immune and inflammatory biomarkers in adult dogs

Spray-dried plasma (SDP) is a high-quality protein source with functional properties that support gut health, immune function, and digestibility. Although its benefits have been demonstrated in various animal species (e.g., swine, poultry, rodents, and fish), further research is needed to understand its specific effects in extruded diets and canine health. This study evaluated the effects of incorporating SDP from swine, in partial replacement of chicken meal, into extruded diets on nutrient digestibility, fecal metabolites, microbiota composition, serum chemistry, and inflammatory and immune biomarkers in adult dogs. Extrusion processing parameters were also evaluated in diets containing increasing levels of SDP. Four dietary treatments were formulated: a Control diet without SDP, a diet with 4% SDP applied as a coating (4% coating diet), and diets with 4% or 8% SDP included within the kibble matrix prior to extrusion. Twelve adult Beagles (n = 12) were assigned to the four dietary treatments in a replicated 4 × 4 Latin Square design, with each diet fed for 21 d following a 7-d adaptation period. All diets were well accepted by the dogs. Feeding 8% SDP maintained overall nutrient digestibility but reduced total dietary fiber digestibility (P < 0.05). Fecal concentrations of short-chain fatty acids, particularly propionate, were higher in dogs fed the 8% SDP diet (193.8 µmol/g) compared with the Control diet (126.8 µmol/g; P < 0.05). Additionally, a linear reduction in protein fermentation byproducts, mainly indole metabolites, was observed, suggesting a beneficial shift in microbial metabolism (P < 0.05). Inclusion of SDP also modulated fecal microbiota composition, with changes across several genera and increases in beneficial genera such as Lactobacillus, Streptococcus, and Catenibacterium, while also affecting beta-diversity (P < 0.05). Serum chemistry analysis showed lower blood urea nitrogen in dogs fed the 4% Coating SDP (17.8 mg/dL), 4% SDP (18.0 mg/dL), and 8% SDP (16.3 mg/dL) diets compared with the Control diet (19.8 mg/dL; P < 0.05), suggesting improved protein metabolism. Fecal IgA concentrations were higher in dogs fed 8% SDP than the Control diet, indicating potential immunomodulatory effects that may contribute to improved intestinal homeostasis (P < 0.05). These findings support the potential of SDP as a functional ingredient in canine diets, contributing to gut health, metabolic regulation, and immune function in extruded pet food.