Pasture availability and dry matter intake of lactating crossbred cows grazing elephant grass (Pennisetum purpureum, Schum.)

The trial was carried out in Brazil, from April 1992 to October 1993. Avail ability and voluntary dry matter intake (DMI) of elephant grass (Pennisetum purpureum) were evaluated, using three groups of 24 crossbred lactating co ws, grazing (4.5 cows/ha), during three days, paddocks varying in size (607 , 494 and 417 m(2)) according to the resting periods adopted. The following treatments were studied: resting period of 30 days without (30W) and resti ng periods of 30 (30C), 37.5 (37.5C) and 45 (45C) days with 2 kg/day (20.6% crude protein CP) concentrate supplement. From October to June the elephan t grass was the sole forage, while during the dry season, cows received sug arcane plus 1% urea as roughage supplement. The average chemical compositio n of sugarcane mixture was: 10.1% CP, 52.5% neutral detergent fiber (NDF), 31.6% acid detergent fiber (ADF), 58.5% in vitro dry matter digestibility ( IVDMD) and the average daily intake was 1.3 +/- 0.2% of body weight (BW). M ean elephant grass availabilities of paddocks 45C (2423+/-92 kg of DM/ha) w as greater (p < 0.05) than (1745 and 1939 +/- 92 kg of DM/ha) observed, res pectively, for resting periods of 30 and 37.5 days. Daily herbage allowance was similar among treatments (11.3 +/- 0.45 kg of DM/cow), but varied acco rding to the season and year, being higher in summer, intermediate in autum n and spring and lower in winter. As the dry season was more severe in wint er and spring 1993, daily herbage allowance was smaller than that in 1992. Extrusa composition was affected by the resting period (p < 0.05), CP conte nt decreased (0.1%) and NDF increased (0.09%) for each day beyond the 30th day of the resting periods. Total DMI estimated using chromic oxide, was lo wer (p < 0.05) for non-supplemented (2.7 +/- 0.12% BW) than supplemented an imals (3.0 +/- 0.12% BW). The elephant grass DMI varied from 1.2% (winter) and 3.7 +/- 0.10% BW (summer) being similar among experimental treatments, except during the summer. In that season elephant grass DMI was smaller onl y in 45C in relation to 37.5C, while those observed in 30W and 30C were sim ilar and did not differ from 37.5C. The average daily milk production (11.4 kg/cow) did not vary among treatments. Although the 30 day resting period resulted in a better quality herbage intake, it did not reflect a higher DM I or milk production. The season and, consequently, the amount of rainfall influenced the results during the year. (C) 1999 Elsevier Science B.V. All rights reserved.