Evaluation of the forage quality of interseeding birdsfoot trefoil with tall fescue and grazing steers performance on the pastures

摘要

Tall fescue (Festuca arundinacea Schreb.) is the predominate species in the humid pasture region of the USA. It is well adapted and produces forage over much of the year. One disadvantage, however, is that animal performance on tall fescue pasture is often poor. Interseeding a legume with tall fescue offers a way of enhancing forage quality, thus improving animal performance while supplying nitrogen for the grass. One perennial legume that grows well in a mixture with tall fescue is birdsfoot trefoil (Lotus corniculatus L.). In order to investigate differences in the performance of steers grazing tall fescue, birdsfoot trefoil and tall fescue-birdsfoot trefoil mixed pastures, and the factors contributing to these differences, experimental pastures were established in April 1997, with endophyte-free tall fescue 'Phyter' and two varieties of birdsfoot trefoil, rhizomatous 'ARS-2622' and non-rhizomatous 'Norcen'. Three studies were conducted over a two-year period after pasture establishment. A grazing study was carried out in spring and fall of 1998, and in spring of 1999. Due to a severe drought in the fall of 1999, no grazing data were collected. Steers grazing birdsfoot trefoil pastures had the highest ADG in the three grazing periods. In 1998, ADG of steers grazing mixed pastures was similar to that of steers grazing tall fescue pastures; in spring 1999, the ADG of steers grazing mixed pastures was greater than that of steers grazing tall fescue pastures. Total weight gain was greater on mixed pastures than on tall fescue pastures in three grazing periods. Using esophageally cannulated heifers, it was determined that cattle selected forage with lower NDF and higher CP contents from mixed pastures than from tall fescue pastures, and the percentage of birdsfoot trefoil selected by cattle was greater than what was actually presented in the mixed pastures. From an in situ study, it was revealed that differences in chemical components in birdsfoot trefoil, tall fescue and tall fescue-birdsfoot trefoil mixed pasture forages were reflected by their different ruminal degradation of DM, ADF and CP. Birdsfoot trefoil monoculture had the fastest DM degradation rate and greatest overall DM degradation among the treatments. The 24-hr DM degradation was least in tall fescue. The DM degradation rate of mixed pasture forage was similar to that of tall fescue pasture forage in spring of 1998, but greater in fall of 1998. These data indicated that the forage quality was best in birdsfoot trefoil and poorest in tall fescue. Forage yield of 'Norcen' and tall fescue mixed pasture was greater or similar to that of tall fescue pasture, while 'ARS-2622' and tall fescue mixed pasture had even lower forage yield than that of tall fescue pasture in spring 1999. Therefore, the best performance of steers grazing birdsfoot trefoil was attributed to the high quality of this legume. Forage yield and quality were not the only reasons for the different performance of steers grazing mixed pastures and tall fescue pastures. The improved performance of steer grazing mixed pasture over tall fescue was attributed to high forage quality, selectivity by cattle, and greater in situ DM degradation and CP utilization of forages from the mixed pastures.