Mulberry Silage as Alternative to Soybean Meal Protein in Ruminant Diet: Effect on Growth Performance, Digestion, Antioxidant Capacity, and Carcass Characteristics of Goats

Current research is still striving to maximize the expansion of protein feed sources in order to reduce the production costs of the livestock industry. In this context, the current study aimed to evaluate the impacts of replacing soybean meal protein in diets with mulberry silage (at 50 and 100% substitution levels) on the growth, health status, and carcass characteristics of growing goat kids. Forty-five Xiangdong black goat kids weighing 18.2 ± 1.6 kg (approximately 6 months old) were divided into three experimental groups and fed one of the following diets: a control diet consisting of a 50:50 concentrate-to-roughage ratio on a dry matter basis (control), a diet replacing 50% of soybean meal protein with mulberry silage (MS-50), or a diet replacing 100% of soybean meal protein with mulberry silage (MS-100). The results show that replacing soybean meal protein with mulberry silage significantly increased (<i>p</i> < 0.05) the intakes of dry matter (DMI), crude protein (CPI), neutral detergent fiber (NDFI), and organic matter (OMI). However, no significant (<i>p</i> > 0.05) differences were observed in the digestibility of dry matter (DM), crude protein (CP), ether extract (EE), or neutral detergent fiber (NDF) among the groups, whereas the digestibility of OM and acid detergent fiber (ADF) was significantly reduced (<i>p</i> < 0.05) in the MS-100 group. Additionally, the MS-100 group exhibited significantly higher (<i>p</i> < 0.05) plasma total protein, albumin, and calcium levels. Total antioxidant capacity (TAC) was significantly enhanced in both the MS-50 and MS-100 groups compared to the control, although the MS-100 showed a significant increase (<i>p</i> < 0.05) in malondialdehyde (MDA) levels related to the other groups. In terms of growth performance, the MS-100 group improved (<i>p</i> < 0.05) final body weight, average daily gain, and carcass weights. Meanwhile, the MS-50 group recorded the highest contents (<i>p</i> < 0.05) of the following amino acids: aspartic acid, threonine, serine, glutamic acid, alanine, lysine, and proline. Overall, the results of the present study indicate that replacing soybean meal protein with mulberry silage generally produced comparable impacts, with additional positive effects on growth performance, meat quality, and health status of goats.