Gunter S A, McCollum F T, Gillen R L, Krysl L J
Oklahoma Agricultural Experiment Station, Stillwater 74078-0102, USA.
J Anim Sci. 1995 Apr;73(4):1174-86. doi: 10.2527/1995.7341174x.
Beef cattle fitted with esophageal (four steers/pasture) or ruminal and duodenal (six calves/pasture; beginning BW +/- SE = 267 +/- 6 kg) cannulas grazed midgrass prairie rangeland (excellent range condition; MIDGRASS) or plains bluestem (Bothriochloa ischaemum var. Plains) pasture (BLUESTEM) in mid-May, late-June, mid-August, and mid-October of 1990 and 1991. Nitrogen in masticate samples collected from MIDGRASS was lowest (P < .05) in June and August across both years. The N in BLUESTEM masticate peaked (P < .05) in August 1990, but N was lowest (P < .05) in August 1991. The detergent fiber content of masticate from both forages increased (P < .05) as the grazing season advanced from May through August; fall regrowth in October occasionally resulted in a small decrease (P < .05) in fiber content. In vitro OM disappearance (IVOMD) followed a pattern similar to N content. The IVOMD of BLUESTEM masticate was greater (P < .05) than that of MIDGRASS masticate. The ruminal ammonia N concentration (milligrams/deciliter) in cattle grazing BLUESTEM (4.5) usually was greater (P < .05) than in cattle grazing MIDGRASS (3.3). In situ OM and N disappearance was greater (P < .05) from BLUESTEM masticate than from MIDGRASS masticate in May, June, and August. The ruminally degraded N:ruminally degraded OM ratio (grams/kilograms) estimated from in situ digestion suggested that cattle grazing MIDGRASS during the mid-summer of both years and BLUESTEM in August 1991 may have been marginally deficient in ruminally degraded N. Plains bluestem pasture would complement MIDGRASS by providing better quality grazing during the mid-summer.
装有食管瘘管（每块牧场4头阉牛）或瘤胃和十二指肠瘘管（每块牧场6头犊牛；初始体重±标准误=267±6千克）的肉牛，于1990年和1991年的5月中旬、6月下旬、8月中旬和10月中旬，在中草草甸草原牧场（优良牧场条件；中草牧场）或平原须芒草（Bothriochloa ischaemum var. Plains）牧场（须芒草牧场）放牧。在这两年的6月和8月，从中草牧场采集的咀嚼样本中的氮含量最低（P<.05）。须芒草牧场咀嚼样本中的氮含量在1990年8月达到峰值（P<.05），但在1991年8月最低（P<.05）。随着放牧季节从5月持续到8月推进，两种牧草咀嚼样本中的洗涤纤维含量均增加（P<.0）；10月的秋季再生偶尔会导致纤维含量略有下降（P<.05）。体外有机物消失率（IVOMD）呈现出与氮含量相似的模式。须芒草牧场咀嚼样本的IVOMD高于（P<.05）中草牧场咀嚼样本。放牧须芒草牧场的牛的瘤胃氨氮浓度（毫克/分升）（4.5）通常高于（P<.05）放牧中草牧场的牛（3.3）。在5月、6月和8月，须芒草牧场咀嚼样本的原位有机物和氮消失率高于（P<.05）中草牧场咀嚼样本。根据原位消化估计的瘤胃降解氮：瘤胃降解有机物比率（克/千克）表明，在这两年的仲夏放牧中草牧场以及在1991年8月放牧须芒草牧场的牛，瘤胃降解氮可能略有不足。平原须芒草牧场可以通过在仲夏提供质量更好的牧草来补充中草牧场。
