This study was conducted to investigate the substitution effect of the concentrate mix (CM) with sweet potato vine (SPV) on growth performance, carcass characteristics of rams, and methane (CH4) production. Forty yearling rams with an initial body weight of 18.5 ± 0.7 kg were randomly distributed into five treatment diets with eight rams each. A CM of 385 g/head/d was supplied to the control group (SPV0), and diets were formulated to replace the CM of the control diet with SPV at 10% (SPV10), 20% (SPV20), 30% (SPV30), and 40% (SPV40). After 82 days, four rams from each treatment were randomly selected and slaughtered. The CH4 production was determined from 24‐h in vitro gas production (GP), and the digestible organic matter (dOM) and metabolizable energy (ME) were estimated from the GP. Data were analyzed using the one‐way ANOVA and orthogonal polynomial contrast functions. Results indicated that the contents of the crude protein (CP) and ash in SPV were 258 and 148 g/kg DM, respectively. The substitution of CM with SPV in the in vivo trial did not affect body weight gain, feed intake, and feed conversion ratio (FCR). Rams fed with the SPV0 diet had higher (p < 0.05) hot carcass weight than those reared in the SPV10, SPV20, and SPV40 diets. The slaughter weight and dressing percentage showed significant linear and quadratic effects. Moreover, significant linear and cubic trends were noted for hot carcass, thorax, foreleg, and hindleg. The SPV0 diet had the highest GP (p < 0.001) compared to the SPV30 and SPV40 diets. The SPV40 diet and the pure SPV had the lowest CH4 production (p < 0.001). The SPV0 diet showed similar ME with SPV10 and SPV20 diets but was higher (p < 0.001) than the SPV30 and SPV40 diets and pure SPV. The dOM did not differ between treatment diets. Similarly, the dOM of SPV did not differ (p > 0.05) from that of the SPV30 and SPV40 diets. In conclusion, replacing CM with SPV significantly reduced the in vitro CH4 production without affecting voluntary feed intake, weight gain, some carcass components, and dOM.
