[Milk production on Cynodon nlemfuensis alone and associated with Arachis pintoi or Desmodium ovalifolium]

The present study was carried out at CATIE's Animal Production Research Station in Turrialba, Costa Rica (9 degrees 53' N; 83 degrees 38' W; 639 m.a.s.l; 22.3 degrees C; rainfall 2636 mm/year, but only 1 month with a negative hydric balance), in order to evaluate the effects of Arachis pintoi CIAT 17434 and Desmodium ovalifolium CIAT 350 on pasture dynamics, selectivity, herbage quality and milk production, when those legumes were oversown in African stargrass (Cynodon nlemfuensis) degraded pastures. The pasture treatments (grass alone and the two grass/legume mixtures) were randomly distributed in two blocks, with two paddocks of each pasture per block. The pastures were rotationally grazed, with 3 or 5 days of occupation depending on paddock size (937 and 1406 m(2), respectively), but the whole grazing cycle lasted 26 days. The experimental design used was a Change Over Latin Square with seven, two, and one replicates over time, when milk yield and composition, selectivity, and intake were measured. Each replicate (phase) involved three pairs of Criollo x Jersey crossbred milking cows (or oesophageal fistulated steers) and three periods of 16 days. In all periods, the cows were allowed to adjust to the new pastures for 6 days; this was followed by a 10-day measurement period, and the 26-days cycle was completed by grazing African-stargrass in monoculture. The stocking rates used were 2.9 AU/ha for the first three phases (January-September 1990), and 2.4 AU/ha for the last four phases (May-October 1991/January-July 1992). In all grazing cycles the changes in total, green and senescent forage biomass availability were monitored, as well as their nutritive value (CP content and IVDMD) before and after grazing, botanical composition of the pastures before grazing, and milk yield and composition. Diet composition and quality were determined during the minimum and maximum rainfall periods (February and June) of 1992, and pasture intake was measured only in June 1992. On the other hand, the blood urea concentration was determined during the first three phases of this study, whereas the concentration of urea in milk was determined only in the last two phases. The results obtained in this study showed not only the comparative advantages of Arachis pintoi over Desmodium ovalifolium in terms of nutritive value and palatability, but also its beneficial effects on the availability and quality of the forage on offer. The voluntary intake, CP content, and IVDMD of the diet selected by cows grazing the African stargrass/A. pintoi mixture were 28.1, 33.6, and 13.0 percent higher than those obtained for the African stargrass pastures