Gunter S A, McCollum F T, Gillen R L, Krysl L J
Oklahoma Agricultural Experiment Station, Stillwater 74078-0102.
J Anim Sci. 1993 Dec;71(12):3432-41. doi: 10.2527/1993.71123432x.
In mid-May, beef cattle fitted with esophageal (four steers/pasture) or ruminal and duodenal cannulas (six heifers/pasture; 274 +/- 6 kg BW +/- SE) grazed midgrass prairie (excellent range condition; PRAIRIE) or a seeded mixture of sideoats grama (48% of pasture DM) and sweetclover (6% of pasture DM; Bouteloua curtipendula [Michx.] Torr./Melilotus officinalis [L.] Lam.; PASTURE). Masticate NDF, ADF, and in vitro OM disappearance did not differ (P > .11) between forage types (average = 66.6, 36.1, and 58.8% of OM). Only N differed (P = .02) between PRAIRIE (2.1) and PASTURE (2.4% of OM). Extents of in situ OM and N disappearance were greater (P < .05) and rate of N disappearance between 12 and 36 h was slower (P < .10) from PRAIRIE than from PASTURE masticate. Based on in situ data, the ruminally degraded N: ruminally degraded OM (grams/kilogram) ratio differed (P < .05) between PRAIRIE (22) and PASTURE (25). Ruminal ammonia N concentration (milligrams/deciliter) was less (P = .02) for PRAIRIE (2.8) than for PASTURE (3.8). Forage OM intake and fecal OM output did not differ (P > .72; average = 8,207 and 3,380 g/d), but duodenal OM flow tended (P = .13) to be greater (PRAIRIE = 4,892, PASTURE = 5,170 g/d) in cattle grazing PASTURE. Apparent and true ruminal OM digestion did not differ between forage types (P > .18; average = 38.3 and 48.5%). Nitrogen intake, nonammonia N, and forage N flow at the duodenum were greater (P < .04) for PASTURE (198 vs 171, 242 vs 210, and 162 vs 135 g/d) than for PRAIRIE. Microbial N flow (average = 78 g/d) and microbial efficiency (average = 20 g of microbial N/kg of OM truly fermented) did not differ (P > .25) between forage types. Apparent and true ruminal N digestion did not differ (P > .65; average = -26.6 and 19.3%) between forage types. Flow of nonammonia N was in excess relative to digestible OM intake; hence, digestible OM intake seemed to be first-limiting for performance by cattle grazing either forage type.
5月中旬，装有食管瘘管（每块牧场4头阉牛）或瘤胃和十二指肠瘘管的肉牛（每块牧场6头小母牛；体重274±6千克，平均体重±标准误）在中草草甸（优良牧场条件；草甸）或由垂穗草（占牧场干物质的48%）和草木樨（占牧场干物质的6%；垂穗草[米契尔]托尔/草木樨[林奈]拉姆；牧场）组成的播种混合草地上放牧。不同牧草类型之间的咀嚼中性洗涤纤维、酸性洗涤纤维和体外有机物消失率没有差异（P>.11）（平均占有机物的66.6%、36.1%和58.8%）。只有草甸（2.1）和牧场（2.4%的有机物）之间的氮含量存在差异（P=.02）。与牧场牧草相比，草甸牧草的原位有机物和氮消失程度更大（P<.05），12至36小时之间的氮消失速率更慢（P<.10）。根据原位数据，草甸（22）和牧场（25）之间瘤胃降解氮与瘤胃降解有机物（克/千克）的比例存在差异（P<.05）。草甸的瘤胃氨氮浓度（毫克/分升）（2.8）低于牧场（3.8）（P=.02）。牧草有机物摄入量和粪便有机物产量没有差异（P>.72；平均分别为8207和3380克/天），但在牧场放牧的牛的十二指肠有机物流量有增加的趋势（P=.13）（草甸=4892，牧场=5170克/天）。不同牧草类型之间的表观和真胃瘤胃有机物消化率没有差异（P>.18；平均分别为38.3%和48.5%）。牧场的氮摄入量、非氨氮和十二指肠处的牧草氮流量高于草甸（P<.04）（分别为198对171、242对210和162对135克/天）。不同牧草类型之间的微生物氮流量（平均=78克/天）和微生物效率（平均=20克微生物氮/千克真正发酵的有机物）没有差异（P>.25）。不同牧草类型之间的表观和真胃瘤胃氮消化率没有差异（P>.65；平均分别为-26.6%和19.3%）。非氨氮流量相对于可消化有机物摄入量过量；因此，可消化有机物摄入量似乎是限制两种牧草类型放牧牛生长性能的首要因素。
