Palatability and apparent total tract macronutrient digestibility of retorted black soldier fly larvae-containing diets and their effects on the fecal characteristics of cats consuming them

There is a growing interest in using black soldier fly larvae (BSFL) due to its supposed sustainability and nutritional qualities. Because little research has been conducted to evaluate the use of BSFL in cats, our objective was to determine the palatability and apparent total tract macronutrient digestibility (ATTD) of BSFL-containing canned diets and the fecal characteristics of healthy adult cats consuming them. First, three palatability tests were conducted to compare the following diets: 1) diet with poultry byproduct meal (PBPM) and chicken serving as the primary protein sources (control) vs. diet with BSFL meal replacing PBPM (BSFL meal); 2) control vs. diet with whole BSFL replacing some PBPM and poultry fat (BSFL whole); and 3) control vs. diet with BSFL oil replacing poultry fat (BSFL oil). All diets were formulated to meet Association of American Feed Control Officials nutrient profiles for adult cats and were produced using a still retort. A paired t-test was conducted to analyze data from each palatability test, with a higher (P < 0.05) consumption ratio being observed for BSFL meal (1.93:1), BSFL whole (2.03:1), and BSFL oil (1.57:1). Second, 32 adult cats (20 females and 12 males; BW: 4.19 +/- 0.55 kg; age: 3.3 +/- 0.38 yr) were used in a completely randomized design study composed of a 21-d baseline period and a 70-d experimental period. Cats consumed the control diet during the baseline and were then allotted to one of four experimental diets (n = 8 per group): 1) control, 2) BSFL meal, 3) whole BSFL, and 4) BSFL oil. Fecal samples were collected after baseline and experimental periods for ATTD and fecal characteristic analysis. Fecal output was higher (P < 0.05) and fecal dry matter percentage was lower (P < 0.05) in cats fed BSFL meal than those fed BSFL oil. Organic matter, crude protein (CP), and energy ATTD were lower (P < 0.05) in cats fed BSFL meal than those fed BSFL oil or control. CP and energy ATTD were lower (P < 0.05) in cats fed BSFL whole than those fed BSFL oil. A few serum metabolites were affected by diet (P < 0.05) but remained within reference ranges. Hematology was not affected by diet (P > 0.05). Overall, our results suggest that BSFL-containing diets are palatable and do not negatively affect fecal characteristics or serum chemistry but may have slightly lower nutrient digestibilities in adult cats. This study demonstrated that black soldier fly larvae-containing canned diets were palatable to cats and did not negatively affect fecal characteristics or serum chemistry but may lead to slightly lower nutrient digestibilities. Lay Summary The pet food industry is interested in black soldier fly larvae (BSFL) because of its supposed sustainability and nutritional qualities. BSFL has not been well tested in cats, so our objective was to determine the palatability and apparent total tract macronutrient digestibility (ATTD) of BSFL-containing canned diets and how they affected the fecal characteristics of adult cats. Palatability tests were conducted to compare diets containing BSFL meal, whole BSFL, or BSFL oil against a poultry-based control. Higher consumption ratios were observed for all BSFL-containing diets. A second study determined the digestibility of BSFL-containing diets and how they affected fecal characteristics. Cats were allotted to a control diet or diets containing BSFL meal, whole BSFL, or BSFL oil. Fecal output was higher and fecal dry matter percentage was lower in cats fed BSFL meal than those fed BSFL oil. Organic matter, crude protein (CP), and energy ATTD were lower in cats fed BSFL meal than those fed BSFL oil or control. CP and energy ATTD were lower in cats fed whole BSFL than those fed BSFL oil. Overall, BSFL-containing diets were shown to be palatable and did not negatively affect fecal characteristics, but reduced nutrient digestibilities in adult cats.