| dc.description.abstract | Seasonal fluctuations in forage availability and nutritive value limit productivity in forage-based beef cattle systems in the southeastern United States. Although forbs have the potential to improve forage diversity, nutritional quality, and pasture resilience, they remain largely underappreciated and underutilized in U.S. grazing systems. Integrating forbs into grass-dominated pastures may improve forage quality and animal performance; however, adoption remains limited due to variability in establishment, productivity, and the presence of plant secondary metabolites that may influence nutrient utilization and rumen fermentation. The objectives of this research were to (1) evaluate the establishment, yield potential, and nutritive value of cool- and warm-season forage forb species across Alabama, and (2) determine how the best-performing warm-season forbs species from the first study would influence nutrient utilization, rumen fermentation characteristics, and methane (CH4) emissions in beef cattle. To achieve the first objective, a randomized complete block design with three field replications per location was conducted at three sites across Alabama and repeated under greenhouse conditions. A total of 24 cool-season forage species, and 12 warm-season species were planted at each location in both years. Differences among species were observed for dry matter yield (DMY; P < 0.01), neutral detergent fiber (NDF; P < 0.01), acid detergent fiber (ADF), and acid detergent lignin (ADL; P < 0.01) among species in the field in both seasons. Crude protein concentration (CP) also differed among species (P < 0.01), with hairy vetch (27%) in the cool season and cowpea (20%) in the warm season exhibiting high protein concentrations. Among cool-season species, hairy vetch and mustard produced the greatest yields (7750 and 6453 kg DM/ha, respectively), whereas sunn hemp (31421.7 kg DM/ha) and cowpea (20189.6 kg DM/ha) were most productive during the warm season. Sunn hemp (Crotalaria juncea L.; SUN), lablab (Lablab purpureus [L.] Sweet; LAB), and soybean (Glycine max [L.] Merr; SOY) were supplemented with bahiagrass (Paspalum notatum Flueggé) in an in vivo metabolism experiment arranged as a 4 × 4 Latin square design. Columns represented experimental periods, and rows represented ruminally-fistulated steers. Dietary treatments consisted of a 70:30 bahiagrass-to-forb ratio, with a grass-only treatment serving as the control (CON). The forb ratio in the diet differed among treatments (P = 0.06) and remained below the targeted inclusion ratio of 30%. While apparent dry matter digestibility (DMD; 56.6–63.1%; P = 0.18), apparent acid detergent lignin digestibility (ADLD; P ≥ 0.18) were not different among diets, apparent neutral detergent fiber digestibility (NDFD; P = 0.03) and apparent acid detergent fiber digestibility (ADFD; P = 0.04) were influenced by diet. Apparently absorbed nitrogen and apparentily retained nitrogen (AAN and ARN, respectively) did not differ among diets (P ≥ 0.39). Differences in vivo dry matter digestibility were expected to follow a similar pattern, as the diet was mostly dominated by bahiagrass. However, there was an effect (P = 0.02) on in vitro dry matter digestibility (IVDMD) of the bahiagrass control substrate and no effect (P = 0.92) of diet for the bahiagrass-forb incubations. There was an interaction of diet and substrate (P = 0.04) for potential activity for methane production (PAMP). Supplementing bahiagrass hay with leguminous forbs improved ruminal fermentation profiles (P ≤ 0.01). Results from both studies indicated considerable variation among species in both yield and nutritional composition, highlighting several forb species with strong potential for integration into southeastern grazing systems. Overall, forb species can contribute to improved forage diversity and nutritional value in southeastern pasture systems while influencing rumen fermentation and CH4 production. | en_US |
