Hardt P F, Ocumpaugh W R, Greene L W
Texas A&M University, Texas Agricultural Experiment Station, College Station 77843.
J Anim Sci. 1991 Jun;69(6):2310-20. doi: 10.2527/1991.6962310x.
Thirty yearling Santa Gertrudis-sired heifers (average initial weight 238 kg) were continuously grazed (five heifers/pasture) on six 2-ha oat-wheat small grain pastures for 112 d to determine the effect of fertilization of pastures with urea (U) vs ammonium sulfate (AS) on mineral status and performance of heifers. Pastures were fertilized with either U, at 200 kg/ha, or AS, at 438 kg/ha, to provide 92 kg of N/ha in November 1987 and March 1988. Ammonium sulfate provided 107 kg of S/ha. Forage samples were collected during each month. Heifers were initially weighed following an overnight fast and at the end of four consecutive 28-d intervals (Periods 1 to 4). Serum and ruminal fluid were collected on d 56 and 112. Pastures fertilized with AS had a greater (P less than .10) in vitro dry matter disappearance during Periods 2 and 3. Ammonium sulfate-fertilized pastures had greater than (P less than .05) S concentrations from January 29 through termination of the trial. There were no differences in ADG (P less than .28) or gain/ha (GPH; P less than .43) over 112 d; however, heifer ADG was greater (P less than .08) in Period 3 and tended to be greater (P less than .16) in Period 2 for those animals grazing U-fertilized pastures. Pastures receiving AS produced less (P less than .04) GPH during Period 2. Ammonium sulfate fertilization in this trial had no effect on forage K, Ca, P, Mg, Cu, or Mo mineral concentrations or on serum mineral and ruminal VFA concentrations, but it did result in an increase in IVDMD and a trend for decreased ADG apparently associated with a decrease in forage intake.
30头一岁龄的圣格特鲁迪斯种公牛所生的小母牛（平均初始体重238千克）在6块2公顷的燕麦 - 小麦小粒谷物牧场上持续放牧（每块牧场5头小母牛），为期112天，以确定用尿素（U）和硫酸铵（AS）对牧场施肥对小母牛矿物质状况和生产性能的影响。1987年11月和1988年3月，牧场分别以200千克/公顷的尿素或438千克/公顷的硫酸铵施肥，以每公顷提供92千克的氮。硫酸铵每公顷提供107千克的硫。每月采集牧草样本。小母牛在禁食过夜后最初称重，并在连续四个28天的间隔期（第1至4期）结束时称重。在第56天和112天采集血清和瘤胃液。在第2期和第3期，用硫酸铵施肥的牧场体外干物质消失率更高（P小于0.10）。从1月29日到试验结束，硫酸铵施肥的牧场硫浓度高于（P小于0.05）其他牧场。在112天内，平均日增重（ADG；P小于0.28）或每公顷增重（GPH；P小于0.43）没有差异；然而，对于那些放牧尿素施肥牧场的动物，小母牛在第3期的ADG更高（P小于0.08），在第2期有更高的趋势（P小于0.16）。在第2期，接受硫酸铵施肥的牧场GPH更低（P小于0.04）。在本试验中，硫酸铵施肥对牧草钾、钙、磷、镁、铜或钼的矿物质浓度以及血清矿物质和瘤胃挥发性脂肪酸浓度没有影响，但确实导致体外干物质消失率增加，并且ADG有下降趋势，这显然与采食量减少有关。
