Dietary Fiber Levels as a Sustainability Strategy in Lamb Production: Impacts on Digestion, Behavior, and Rumen Function

Defining appropriate dietary fiber levels is essential for enhancing the sustainability of feedlot lamb production. Optimal dietary fiber levels can enhance meat yield, improve nutrient retention and utilization, and reduce environmental impact. This study aimed to determine the optimal level of dietary fiber to enhance nutrient intake, digestibility, feeding behavior, and rumen fermentation in feedlot lambs. Five rumen-fistulated Santa Inês male lambs (40 kg, 7 months old) were used in a 5 × 5 Latin square design. Diets contained increasing levels of neutral detergent fiber (NDF): 200, 320, 440, 560, and 680 g/kg dry matter (DM), with each period lasting 21 days (total 105 days). Nutrient intake responded quadratically to NDF levels ( p < 0.05). Apparent digestibility was significantly affected ( p < 0.05), except for crude protein. Feeding ( p = 0.001) and rumination times ( p = 0.002) increased linearly, while idling time decreased ( p < 0.001). Feeder visits declined ( p = 0.002), and idling events followed a quadratic trend. Feeding and rumination efficiencies for DM decreased ( p = 0.006 and p = 0.010), while NDF rumination efficiency increased ( p = 0.014). The ruminal pH rose ( p < 0.001), and propionate decreased ( p = 0.019); acetate and butyrate showed quadratic responses. Based on intake, digestibility, and fermentation patterns, dietary NDF should be included at 400 g/kg DM to optimize nutrient utilization and rumen function in confined lambs.