Effects of Dietary Incorporation of Grape Stalks Untreated and Fungi-Treated in Growing Rabbits: A Preliminary Study

Simple Summary The use of winery by-products as an animal feed ingredient in rabbit production can enhance the sustainability of this livestock sector by reducing feeding costs and simultaneously diminishing environmental problems related to the management of those by-products. White-rot fungi have been studied for the delignification of lignocellulosic materials due to their potential to decrease the content of lignin. In fact, white-rot fungi also improve the nutritional value due to the deposition of bioactive compounds, acting as a possible biological treatment to enhance the nutritive value of grape stalks. The objective of this work was to evaluate the incorporation of untreated grape stalks and fungi-treated grape stalks in rabbits' diets. This study aimed to evaluate the effect of the incorporation of untreated grape stalks (U-GS) and fungi-treated grape stalks (Lentinula edodes, T-GS) in rabbits' diets. The control group was fed with a control diet without grape stalks (C), two experimental groups were fed on diets with 5% and 10% incorporation of U-GS (5U(GS) and 10U(GS)), and two with 5% and 10% incorporation of T-GS (5T(GS) and 10T(GS)). Rabbits fed with T-GS diets showed higher daily weight gain (p = 0.034), feed conversion rate (p = 0.002), carcass weight (p = 0.038), and reference carcass weight (p = 0.03) when compared to the control diet. Moreover, animals fed with T-GS diets showed an increase in the caecum (p = 0.015) and small intestine (p = 0.021) lengths and in the total volatile fatty acid content (p = 0.005) compared to animals fed U-GS diets. Blood triglyceride levels were lower in animals fed with T-GS diets compared to U-GS (p = 0.005) and C (p <= 0.001) diets (12% and 19% lower, respectively), and a trend to lower cholesterol levels was observed (p = 0.071). Meat from rabbits fed with T-GS diets had higher levels of linoleic acid, gamma-linolenic, n-ary sumation omega-6, n-ary sumation PUFA, and n-ary sumation PUFA/ n-ary sumation SFA ratio compared to rabbits fed with the C diet. Results indicated that grape stalks (U-GS and T-GS) could be effectively used as an alternative raw material in rabbits' diets without compromising animal performance.