Enhancing utilization of warm-season forages for beef cattle systems in the southeastern United States
Abstract
In the southeastern United States, grazing systems play a vital role in the nutrition and production of beef cattle. To further improve the efficiency and sustainability of these programs, it is essential to explore the potential of integrating novel forage species and management practices into conventionally managed systems. To achieve this goal, two studies were performed to explore the digestibility and nutritional value of different warm-season forages. The first experiment evaluated the digestibility of mixtures of crabgrass (Digitaria sanguinalis [L.] Scop) and pearl millet (Pennisetum glaucum [L.] R. Br.) alone (G) or in a mixture with 30% forage soybeans (Glycine max [L.] Merr.) (G+L). Warm-season annual forages are highly digestible and commonly used to complement perennial grass pastures, providing cattle with high-quality nutrition during the summer months. Forage in vitro and in situ digestibility analyses were conducted using two ruminally cannulated steers from Auburn University’s Stanley P. Wilson Beef Teaching Center (Auburn, AL). Results indicated that in vitro true digestibility (IVTD) decreased as the season progressed, with G samples declining from 63.5% in June to 45.9% in September (P < 0.01). For G+L, there was also an effect of month (P = 0.01), with August and September being less digestible than June or July. For G, digestibility also differed across incubation times (P < 0.01), with digestion plateauing at 48 h. Results from the in situ study indicated the fractional rate of degradation (kd) for G+L was different among months (P = 0.04) in which June was greater than any other month. The potentially degradable fraction (D) was greatest (P < 0.01) in July for G, but there was no difference (P = 0.2) among months for G+L. For both G and G+L, the undegradable fraction (U) was increased with advancing forage maturity (P < 0.01). This study provides insights into the 2 digestibility and fiber degradation rate of warm-season annual forage mixtures including legumes. The second study was an on-farm demonstration which examined stockpiled bahiagrass (Paspalum notatum Flüggé) at two Alabama locations (Montgomery County and St. Clair County) to assess forage production, nutritive value, and potential use of stockpiled bahiagrass to extend the grazing season during the fall forage production gap. In Year 1, fertilized pastures in St. Clair County produced, 994 kg DM/ha more biomass than unfertilized pastures in Montgomery, AL over a 30-day grazing period. Both locations had similar forage nutritive value, with Montgomery having 7.3% crude protein (CP) and 62.6% total digestible nutrients (TDN) and St. Clair having 6.9% CP and 62.7% TDN. The second year of the study had greater total forage production with a mean yield of 4,364 kg DM/ha across locations compared to Year 1 despite warmer and drier conditions. Forage concentration of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), CP, and TDN were influenced by location, harvest date, and their interaction. Total digestible nutrients decreased with increasing forage maturity across harvest date (P < 0.01). At both sites, producers were able to provide an additional 30 to 40 days per year of grazing on their operation using stockpiled bahiagrass. Results from this study suggest stockpiling bahiagrass could help close the fall forage gap, but protein supplementation may be required to meet the nutritional needs of most beef cattle classes. Overall, these findings highlight the potential of stockpiling bahiagrass and incorporating warm-season annuals into grazing systems to enhance year-round forage availability and better understand seasonal forage nutritive value characteristics for use in beef cattle operations.