Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/1997
Publication Date: N/A
Interpretive Summary: It is generally accepted that as forage plants mature their yield per acre increases while quality of the forage declines. Producers that utilize stored forage in their enterprises must balance the need for high quality with need for high dry matter production per acre. The general convention is that quality declines at a near constant rate with increasing maturity. This study evaluated Kanlow switchgrass when vegetative through heading, using 14-day harvest intervals to assess changes in dry matter intake and digestion. The data show that high daily steer gains of over 2.0 lbs/day can be achieved from switchgrass harvested as hay in early June when vegetative and about 4.0 feet tall. Delaying harvest beyond this maturity greatly reduced both dry matter intake and dry matter digestion. If low daily gains or a maintenance diet is acceptable and higher dry matter yields are needed, a producer should delay harvesting until the mid- -boot or heading stages. This study shows that quality changes rapidly in switchgrass at certain stages of plant maturity while negligible at others. The astute producer will determine the daily response desired for each class of livestock, then harvest switchgrass for hay at the maturity stage to permit the dry matter intake and digestion required to achieve the desired animal response.
Technical Abstract: Five maturities of switchgrass hay harvested at about 14-d intervals, vegetative through 20% heading, were fed to Hereford steers (297 kg) in a five x five latin square. Relationships with switchgrass maturity were negative and quadratic (P<.05) for DMI and cubic (P<.05) for digestible DMI. Declines in apparent digestibilities of DM, ADF, and cellulose were cubic (P<.05) whereas these were quadratic (P<.05) for NDF, hemicellulose and N. The digestible N intake was limited in the more mature hay and may have been a greater factor in limiting forage DM utilization than fiber. Whole masticates, collected via esophageal cannula, from the least, mid- and most mature hays showed linear (P<.05) declines in DM concentration and in vitro dry matter disappearance whereas NDF concentrations increased lin- early (P<.05). Sieving of masticate DM into seven size classes (<.25, .25, .50, 1.00, 1.70, 2.80, and > 4.00 mm) showed a reduced proportion of large particles and an increased proportion of small particles with advancing forage maturity. Mean retention time of gastrointestinal DM increased lin- early (P<.01) from 64 to 94 h and rate of passage declined linearly (P<.01) from 3.3 to 2.1% /h. More than 94% of the sieved fecal DM passed a 1.0- mm sieve and yet particle size of the feces showed the same relationship with maturity as the masticate DM. The associations among animal response, masticate and fecal characteristics revealed the importance of plant matur- ity in the utilization of switchgrass. Shifts in particle size reduction from ingestive mastication were not numerically large, but may affect intake and of rate passage because they were reflected in fecal particle size in spite of comminution from the rumination and digestive processes.