Effect of Supplemented Spent Mushroom Substrate ( Pleurotus ostreatus ) on Growth Performance, Nutrient Digestibility, Nitrogen Balance, and Blood Metabolites of Goats

This study evaluated the effects of Pleurotus ostreatus spent mushroom substrate (SMS), supplemented with 4% urea and 18% molasses, as a partial replacement for Napier grass. Four dietary treatments were formulated with 70% roughage (Napier grass) and 30% concentrate, replacing Napier grass with SMS at 0%, 20%, 35%, or 50% inclusion levels. A 120-day feeding including a 7-day digestibility trial was conducted using 20 3-month-old upgraded Anglo-Nubian goats (7.81 ± 0.39 kg). Goats fed diets containing 20%-35% SMS maintained average daily gain and feed conversion efficiency comparable to the control group, while 50% SMS inclusion significantly reduced both parameters (p < 0.05). Dry matter intake and digestibility of dry matter, organic matter, and crude protein decreased with increasing SMS levels, whereas ether extract digestibility improved. Nitrogen absorption was significantly reduced at higher inclusion levels (p < 0.05). Ruminal pH increased linearly, accompanied by a decrease in total short-chain fatty acids, acetate, and propionate concentrations. Serum glucose, total cholesterol, triglycerides, and creatinine remained within normal ranges, although blood urea nitrogen increased with higher SMS inclusion. Overall, moderate SMS inclusion (up to 35%) supported goat performance and nutrient utilization, while higher levels may limit digestibility and fermentation, indicating the need for additional processing to enhance its feeding value.