In Vivo and In Vitro Digestibility and Fermentation Characteristics of Spent Mushroom Substrate (Pleurotus ostreatus) as a Feed Resource for Small Ruminants.

This study evaluated the nutritional value of spent mushroom substrate (SMS) supplemented with 4% urea and 18% molasses as a partial roughage replacement in small ruminant diets. Four dietary treatments were formulated using 70% roughage (Napier grass) and 30% commercial concentrate, with SMS replacing Napier grass at 0%, 20%, 35%, or 50% inclusion levels. A 4 × 4 Latin square design was implemented in an in vivo digestibility trial using four 6-month-old intact male upgraded Anglo-Nubian goats (21.37 ± 0.35 kg). Using the same inclusion levels as the in vivo trial, in vitro fermentation was conducted using sheep rumen fluid to assess gas and methane production, nutrient degradability, and short-chain fatty acid (SCFA) concentrations. Rumen fluid was analyzed via qPCR to determine microbial abundance. Results showed that dry matter intake increased linearly with SMS inclusion, while dry matter, organic matter, and crude protein digestibility decreased (p < 0.05). Increasing SMS inclusion reduced nitrogen absorption and retention (p < 0.05). In vitro degradability of DM, OM, CP, and fiber, as well as gas, methane, and SCFA production, decreased linearly (p < 0.05), although methanogen abundance increased (p < 0.05). Overall, 20% SMS inclusion, supplemented with urea and molasses, maintained nutrient utilization and fermentation comparable to control, supporting its use as a partial roughage replacement.