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.

Amaranthus hypochondriacus is rich in nutrients and represents a feed resource with significant potential. This experiment aimed to study the effects of different proportions of Amaranthus hypochondriacus stem and leaf powder (AHSL) on intestinal digestive enzyme activities, cecal volatile fatty acids, and the microbiota of broilers. A total of 288 one-day-old male broilers (Ross 308) were randomly assigned to the control diet group and the 3%, 6%, and 9% AHSL diet group for days 0–21. Subsequently, the 3%, 6%, and 9% AHSL diets were switched to 5%, 10%, and 15% AHSL diets for days 22–42. The results demonstrated that the dietary inclusion of AHSL significantly affected sucrase activity in the jejunal mucosa (p < 0.05). The 5% AHSL group exhibited the highest sucrase activity, followed by the control group, both of which showed significantly higher activity compared to the 10% and 15% AHSL groups (p < 0.05). The cecal pH in the 5%, 10%, and 15% AHSL groups was significantly lower than that in the control group (p < 0.05). The contents of acetate, propionate, butyrate, and valerate in the cecum of the 10% and 15% AHSL groups were significantly higher than those of the control group (p < 0.05). The addition of AHSL had no significant effect on the alpha diversity of cecum microorganisms. The relative abundance of Ruminococcaceae_UCG_005 and Lactonifactor was significantly higher in the 10% AHSL group compared to the control group, whereas the 15% AHSL group had a significantly higher relative abundance of Clostridium_sensus_tricto12, Peptoclostridium, Anaerofilum, and Peptococcaceae. In summary, the inclusion of 5% AHSL in the diet enhances sucrase activity in the jejunum of broilers, while 10% or 15% AHSL increases the volatile fatty acid content and reduces the pH value in the cecum, without adverse effects on the cecal microbiota.