CHANGES IN FORAGE QUALITY, INGESTIVE MASTICATION, AND DIGESTA KINETICS RESULTING FROM SWITCHGRASS MATURITY

Five maturities of switchgrass hay harvested at 14-d intervals (vegeta tive through 20% heading) were fed to Hereford steers (297 kg) in a 5 x 5 Latin square. Relationships with switchgrass maturity were negativ e and quadratic (P < .05) for DMI and cubic (P < .05) for digestible D MI. Declines in apparent digestibilities of DM, ADF, and cellulose wer e cubic (P < .05), whereas these were quadratic (P < .05) for NDF, hem icellulose, and CP. Whole masticates from the least, mid, and most mat ure hays showed linear (P < .05) declines in DM concentration and IVDM D with increasing maturity, whereas NDF concentrations increased linea rly (P < .05). Mean retention time of gastrointestinal DM increased li nearly (P < .01) from 64 to 94 h from the least to the most mature hay , and the associated rate of passage declined linearly (P < .01) from 3.3 to 2.1% h. Sieving of masticate DM showed a reduced proportion of large particles (greater than or equal to 2.8 mm) and an increased pro portion of small particles (less than or equal to .5 mm) with advancin g forage maturity. More than 94% of the sieved fecal DM passed a 1.0-m m sieve, but particle sizes showed the same relationship with forage m aturity as noted for masticate DM. This occurred despite the comminuti on from the rumination and digestive processes.