Holden L A, Muller L D, Fales S L
Department of Dairy and Animal Science, Pennsylvania State University, University Park 16802.
J Dairy Sci. 1994 Aug;77(8):2332-40. doi: 10.3168/jds.S0022-0302(94)77176-9.
The objectives were to estimate intake of pasture and total DMI by high producing cows grazing grass pastures and to measure changes in nutrient composition of grass pasture during the grazing season. Sixteen multiparous Holstein cows averaging 31 kg of 4% FCM/d at the start of the trial grazed grass pastures at a stocking rate of 2.5 or 3.9 cows/ha from April until October 1990. Intake was estimated using Cr2O3 as an indigestible fecal marker. Pasture samples were analyzed for nutrient composition at six times during the grazing season corresponding to the times of intake estimation. Total daily DMI increased from 21.3 kg in early spring to 22.4 kg in late spring and then decreased as lactation progressed; however, DMI exceeded NRC recommendations during most of the grazing season. Daily pasture DMI varied with season, ranging from 11.6 to 15.6 kg and was lowest (11.6 kg) in the summer. Estimated NEL intakes were lower than NRC recommendations in early spring. During the grazing season, pasture ranged from 39 to 48% NDF and from 22 to 30% CP with 15 to 20% ruminally degradable protein on a DM basis. Grazing cows consumed adequate DM from pasture except in early spring. Although nutrient composition of pasture varied with season, quality remained high.
研究目的是估算高产奶牛在放牧草地时的牧草采食量和总干物质采食量（DMI），并测定放牧季节内草地营养成分的变化。1990年4月至10月，16头经产荷斯坦奶牛在试验开始时平均日产4%乳脂校正乳（FCM）31千克，以每公顷2.5头或3.9头的饲养密度放牧于草地。采用三氧化二铬（Cr2O3）作为难消化粪便标记物来估算采食量。在放牧季节对应采食量估算时间的六个时间点采集草地样本分析营养成分。每日总DMI从早春的21.3千克增加到晚春的22.4千克，然后随着泌乳进程而下降；然而，在大部分放牧季节DMI超过了美国国家研究委员会（NRC）的建议值。每日牧草DMI随季节变化，范围为11.6至15.6千克，夏季最低（11.6千克）。早春时估算的净能（NEL）摄入量低于NRC建议值。在放牧季节，以干物质计，草地中性洗涤纤维（NDF）含量为39%至48%，粗蛋白（CP）含量为22%至30%，瘤胃可降解蛋白含量为15%至20%。除早春外，放牧奶牛从牧草中采食了足够的干物质。尽管牧草营养成分随季节变化，但质量仍保持较高水平。
