In Vitro Evaluation of Protected Black Soldier Fly Larvae (Hermetia illucens), Palm Oil, and Rice Bran Oil on Rumen Fermentation and Degradability

This study evaluated the effects of protected and non-protected black soldier fly larvae oil (BSFLO), palm oil (PO), and rice bran oil (RBO) on ruminal fermentation characteristics and nutrient digestibility using an in vitro gas production technique. A completely randomized design with a 3 × 3 + 1 factorial arrangement was employed, consisting of three oil sources, three oil forms (non-protected, calcium soap, and potassium soap) supplemented at 4% of dry matter, and a control without oil. The results showed that oil supplementation without the basal diet reduced total volatile fatty acid (TVFA) production and ammonia nitrogen (NH3-N) concentration at 24 h, indicating an inhibitory effect of free fatty acids on rumen microorganisms. With the basal diet, TVFA concentrations at 24 h were higher in oil-supplemented treatments compared to the control. Specifically, protected BSFLO in both Ca-soap and K-soap forms showed the numerically highest TVFA concentrations (127.02 and 125.87 mmol, respectively), although these did not differ significantly from those of RBO Ca-soap and K-soap; BSFLO K-soap had a lower TVFA concentration than the control at 48 h. Oil supplementation significantly modified VFA profiles by decreasing the proportion of acetic acid, increasing propionic acid, and consequently lowering the acetate-to-propionate ratio. Ruminal pH was not affected by oil supplementation. While in vitro dry matter degradability was lower in the oil-supplemented treatments than in the control, IVDMD did not show differences between non-protected oil and protected oil treatments. Abomasal simulated digestion was not adversely affected by oil source or protection form. In conclusion, in the presence of a basal diet, BSFLO in Ca-soap and K-soap forms increased TVFA at 24 h, and BSFLO in all forms increased propionate proportions, without compromising rumen stability or abomasal simulated digestion under the conditions tested. These in vitro results indicate protected BSFLO’s potential as a lipid source in ruminant diets and warrant in vivo confirmation.