| dc.description.abstract | The objective was to investigate forage value throughout the year using near infrared reflectance spectroscopy (NIRS) while comparing sample types. Samples were collected from tallgrass native range pastures being grazed by beef cow-calf pairs (n=6) every month for four years. Samples were dried and separated into leaf and whole plant subsamples, ground through a 1 mm screen and analyzed with NIRS. Results were analyzed by a two-way sample type × month interaction, month and sample type. All NIRS components were affected by month (P < 0.001). Crude protein (CP) had a sample type × month interaction (P = 0.01), and was greatest in May. Acid detergent fiber (ADF), neutral detergent fiber (NDF) and Lignin were not affected by two-way interaction (P = 0.47, P = 0.09, P = 0.07). In May, ADF, NDF and lignin were least. There was no sample effect for ADF (P = 0.30). Lignin and NDF were greater in whole samples (P = 0.03, P = 0.05). In-vitro true dry matter disappearance (IVTDMD) was greater in whole samples during May in a two-way interaction (P = 0.01). There was a significant interaction for NDF digestibility (NDFD48) (P = 0.01). Fructan had no two-way interactions (P = 0.18), but was greatest in May, and not affected by sample type (P = 0.10). Sample type × month interactions for Fat were not significant (P = 0.32). Fat was greatest in the fall and greater in leaf only samples (P = 0.001). Two-way interactions show Starch was greater in leaf samples in June (P = 0.03). Digestible energy (DE), metabolizable energy (ME), total digestible nutrients (TDN), net energy for maintenance and net energy for gain were all affected by sample type × month interactions (P < 0.001), month (P < 0.001), as well as sample type (P = 0.001). These results suggest that time of year is a major factor influencing forage nutritive value and energy value, as expected. Sample separation into leaf matter may affect some components depending on time of year, but not to the degree that was expected. | |
