| James B. Lamb, Don C. Adams, Terry J. Klopfenstein, Rich J. Grant, Phillip L. Sims, Larry M. White, and Steven S. Waller |
| Lamb is former Research Associate and Adams is Professor, Univ. of Nebraska-Lincoln, Institute of Agr. and Natural Resources, West Central Res. and Extension Center, 461 West University Drive, North Platte, Neb. 69101; Klopfenstein and Grant are Professor and Associate Professor, Dept. of Animal Science Univ. of Nebraska-Lincoln 68583; Sims and White are Research Leader and retired, USDA-ARS, Southern Plains Res. Station, Woodward, Okla. 73801; Waller is Professor Dept. of Agronomy Univ. of Nebraska-Lincoln 68583. Correspondence should be addressed: Don Adams, West Central Research and Extension Center, North Platte, Nebr. 69101. |
Abstract |
| Ruminally fistulated steers were used in a 4 x 4 Latin square to test effects of immature (vegetative) and mature (post reproductive) leaf and stem fractions from subirrigated meadow hay on organic matter intake (OMI), organic matter digestibility (OMD), and digestive kinetics. Hay was harvested 1 June (immature) and 1 October (mature), chopped into 3- to 5-cm lengths, then separated into leaf and stem fractions using a modified Clipper Cleaner Model Super 69D. Steers were provided ad libitum access to fractions and supplemented with urea so that diets were iso-nitrogenous. Particulate passage was determined using Yb labeled large hay particles [ 1.7-mm screen] and Er labeled small particles [< 1.7-mm and 0.212-mm screen]. Samples were collected from the rumen, omasum, feces, and un-masticated diets for particle size determination. Particle size was determined using wet sieving techniques. Voluntary OMI of immature fractions (15.4 g kg-1 BW) was greater (P < 0.05) than mature fractions (12.5 g kg-1 BW). Within maturity OMI and OMD of leaves and stems were similar. Immature fractions had greater (P < 0.05) OMD (63.2%) than mature fractions (55.7%). Large and small particle passage rates were faster (P < 0.05) for immature fractions [3.2% hour-1 (large) and 4.3% hour-1 (small)] than mature [(2.3% hour-1 (large) and 2.9% hour-1 (small)]. Critical particle size for ruminal escape was 1.18 mm for both leaves and stems regardless of maturity. Differences in OMI and OMD between immature and mature fractions were explained by changes in structural components of the cell wall that made particles more resistant to mechanical and microbial breakdown. |
| Key Words: digestibility, retention, particle size, rumen, feces, omasum |