This experiment was conducted to determine the nutrient composition of three agricultural by-products, namely garlic peel, sweet potato vine, and cotton straw, calculate their relative feeding value, effective energy value, and other indexes, and comprehensively evaluate their nutrient value by combining with rumen in vitro fermentation technology, with the aim of providing data references for the development and utilization of non-conventional feed resources for ruminants. The results showed that: 1) the dry matter (DM), ash, ether extract (EE), and crude protein (CP) contents of cotton straw were significantly higher than the other two feeds (p < 0.05), while the acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of garlic peel were highly significantly higher than the others (p < 0.05); 2) the relative feed value (DMI, DDM, TDN, RFV, and RFQ) and effective energy value (GE, DE, ME, NE_m, NE_g, and NE_L) indexes of cotton straw were significantly higher than garlic peel and sweet potato vine (p < 0.01); 3) after 48 h of in vitro fermentation, the dry matter degradation rate (IVDMD) of sweet potato vine was significantly higher than the other two feeds (p < 0.01), and the cumulative gas productions (mL) and estimated gas parameters (a, b, a + b, and c) of sweet potato vine were significantly (p < 0.01) higher than those of garlic peel and cotton straw; 4) the sweet potato vine had lower pH but higher NH₃-N compared to garlic peel and cotton straw (p < 0.05). The sweet potato vine had higher propionate, iso-butyrate, butyrate, iso-valerate, and total VFA than the other two roughages, which also had the lowest acetate-to-propionate ratio. Garlic peel produced the lowest acetate, while it produced the highest valerate (p < 0.05). These findings demonstrate that all three by-products have high potential as livestock feed based on their nutritive value parameters. Comparatively, sweet potato vines exhibit higher feeding value due to their relatively moderate NDF content and superior rumen fermentation performance.

Optimizing protein nutrition in ruminants is vital for enhancing growth performance, meat quality, and overall production efficiency. However, the precise protein requirement for ruminants remains unclear. Two experimental trials were conducted to investigate the impact of varying levels of rumen-undegradable protein (RUP) on in situ feed degradability, growth performance, meat quality, and rumen fermentation parameters in fattening Hu sheep. In EXP 1, six Hu sheep were fitted with rumen fistulas to measure rumen degradation characteristics of diets varying levels of crude protein (CP) (13%, 14%, 15%, and 16% X RUP: CP 40%, 45%, 50%). The results showed that the ruminal DM and GE degradation had no difference between the experimental diets (p > 0.05). However, the CP degradation rate gradually decreased as the dietary RUP proportion increased (p < 0.05). In EXP 2, a double factorial experiment was conducted using 720 male Hu sheep, divided into twelve dietary treatments with varying levels of crude protein (CP) (13%, 14%, 15%, and 16%) and RUP (40%, 45%, and 50%). Key performance indicators such as body weight gain (BWG), average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were measured at the beginning and end of the trial. Post-slaughter, meat quality attributes, including drip loss and initial pH of the longissimus dorsi muscle, were assessed after 40 days of the trial. Rumen fluid samples were analyzed for volatile fatty acid (VFA) profiles to evaluate rumen fermentation efficiency. The results demonstrated that increasing RUP levels significantly improved BWG and ADG (p < 0.05) without affecting ADFI and FCR. Although dietary protein levels had minimal impact, higher RUP levels were associated with a trend toward increased final body weight (p = 0.09). Dietary protein levels and the RUP: CP ratio had no significant effect on meat quality (p > 0.05). Ruminal acetate, valerate, and iso-valerate concentrations were reduced as RUP: CP increased (p < 0.05), and propionate concentration showed a similar trend (p = 0.062). In conclusion, optimizing RUP levels in the diets of fattening Hu sheep significantly enhances growth performance without compromising feed efficiency or the overall rumen fermentation process. These findings provide a foundation for developing feeding strategies that maximize production efficiency in sheep farming.