Effects of Feeding Regime and Finishing Duration on Growth Performance, Meat Quality, Rumen Fermentation, and Microbiota in Black Angus Bulls.

Optimizing feeding regimes and finishing duration is essential for improving beef production efficiency and meat quality. This study evaluated the effects of two feeding regimes and three finishing durations on growth performance, nutrient digestibility, carcass traits, meat quality, blood biochemical parameters, rumen fermentation, and rumen microbiota in Black Angus bulls. A total of 552 healthy bulls with similar initial body weight were assigned to a 2 × 3 factorial design with two diets-a corn silage-rice straw-concentrate TMR (CSRC) and a rice straw-concentrate TMR (RSC)-and three finishing durations: 10, 12, and 14 months. The CSRC TMR increased average daily gain and reduced feed-to-gain ratio during early finishing (p < 0.05), whereas the RSC TMR resulted in greater final body weight and higher meat redness at 14 months (p < 0.05). Prolonged finishing decreased average daily gain, feed efficiency and nutrient digestibility (p < 0.05), but increased carcass weight, eye muscle area, backfat thickness and meat tenderness (p < 0.05). The CSRC TMR promoted higher total volatile fatty acid production (p < 0.05), an acetate-oriented fermentation pattern and greater rumen microbial alpha diversity. These findings support a stage-specific feeding regime for Black Angus bull finishing. Under the present conditions, corn silage inclusion may be used to improve early finishing efficiency, whereas rice straw-concentrate TMR may be more suitable for late finishing to balance final body weight, meat quality, and production cost.