Comparison of Forage Sampling Method to Determine Nutritive Value of Bahiagrass Pastures

The objective of this study was to compare the nutritive value of forage selected by grazing cattle (masticate) with hand-collected forage samples from bahiagrass (Paspalum notatum Flüggé) pastures. Forage and masticate samples were collected monthly at 4 locations within the state of Florida. Chemical composition of forage and masticate samples was determined and selection indices (SI = {[(masticate - hand-sampled analyte concentration)/hand-sampled analyte concentration]  × 100} + 100) were calculated for in vitro digestible OM, CP, and ADF concentrations. Hand shears were used to collect hand-sampled forage, and masticate samples were collected using ruminally fistulated steers. Masticate samples had greater (P ≤ 0.001) in vitro digestible OM and CP concentrations and lower (P < 0.001) ADF concentration than hand-collected forage samples (60.0 vs. 48.7, 11.7 vs. 10.0, and 34.4 vs. 29.4%, respectively). A sampling type × month interaction (P ≤ 0.006) existed for IVOMD, CP, and ADF during the study. The SI was greatest (P < 0.001) in the winter months in January and February for IVOMD, whereas the SI was lowest in June. The SI for ADF was lowest (P < 0.001) in February, March, and November compared with other months. Selection of CP tended (P < 0.06) to be affected by month. Throughout the year, steers were able to selectively graze bahiagrass forage and consume a diet better than what would be predicted by collecting hand-sampled forage. Ultimately, understanding selection differences could influence supplementation decisions for cattle grazing subtropical forages.