Pastagens de capim-marandu sobressemeado com forrageiras de inverno ou em cultivo exclusivo: produtividade, estrutura do pasto e desempenho animal

Abstract

The objective of this study was to understand the relationship between the structure of the marandugrass pasture overlapping with winter forages or in exclusive cultivation on the performance of 3 /4 Zebu x 1⁄4 Holstein heifers subjected to grazing at variable stocking rate during the winter period. Fifteen heifers per treatment were used in a completely randomized design, in a subdivided plot scheme, with three replicates (pickets). The main plots consisted of pasture types: marandu grass overgrown with a mixture of white oats (Avena sativa L.) cv. IPR 126, black oats (Avena strigosa Scherb) cv. common and annual ryegrass (Lolium multiflorum L.) cv. common (M. + Av + Az); Marandu grass overgrown with white oats (Avena sativa L.) cv. IPR 126, with legumes: white clover (Trifolium repens L.) and red clover (Trifolium pratense L.) (M. + Av + Tr) and marandu grass in exclusive cultivation (M.ex.) And subplots grazing cycles (1st cycle: 21/06 to 20/07, 2nd cycle: 21/07 to 19/08, 3rd cycle: 20/08 to 18/09). There was no interaction between grazing types and grazing cycles. The highest green dry matter yield (2,750.50 kg ha-1) was obtained in the third grazing cycle in relation to the first cycle (1,779.94 kg ha-1). In the third grazing cycle, the highest grazing rate (12.69 AU ha-1) and lowest grazing cycle (10,15 UA ha-1) were obtained. In the pasture of marandu grass in exclusive cultivation, a greater forage supply was obtained (10,11 kg of DM 100-1 kg of PV) and lower supply of forage (5,68 kg of DM 100-1 kg of PV) in the firstgrazing cycle. There was interaction between pastures and grazing cycles for foliar leaf volumetric density, with higher values in the last grazing cycle in the pasture of marandugrass overgrown with oats and clover (69,95 kg ha-1 cm-1) and lower in marandu grass overshadowed with oats and ryegrass (29,21 kg ha-1 cm-1 ). The pasture of marandugrass overgrown with oats and ryegrass provided the highest daily gain (1,15 kg animal-1 day-1 ) in the last grazing cycle in relation to the first cycle (0,93 kg animal-1 day-1 ) and the intermediate cycle (0,77 kg animal-1 day-1 ). In the exclusive cultivation of marandu grass, the lowest daily gain (0,85 kg animal-1 day-1 ) was obtained in the first grazing cycle. In the second grazing cycle, the pasture of marandu grass overgrown with oats and clover provided higher average daily gain (0,93 kg animal-1 day-1). The highest gain per area was obtained in the first grazing cycle in the pasture of marandu grass overgrown with oats and ryegrass (296,85 kg ha-1) in relation to the pasture of marandu grass overgrown with oats and clover (167,78 kg ha-1). In the second grazing cycle, the pasture of marandu grass overgrown with oats and clover provided lower gain per area (59,85 kg ha-1). In the last grazing cycle, the pasture of marandu grass with oats and ryegrass yielded the highest gain per area (881,40 kg ha-1). All pastures favored the highest gain per area in the last grazing cycle (881,40 kg ha-1 ; 483,16 kg ha-1 ; 526,75 kg ha-1 for the pasture of marandugrass overgrown with oats and ryegrass , with oats and clover and in exclusive cultivation respectively). The strategy of overestimating winter grasses in Marandu grass pastures, under the edaphoclimatic conditions of central-northern Minas Gerais State, does not provide significant increases in forage productivity nor does it alter the structural characteristics of overgrown pastures that promote increases in the performance of crossbred heifers. Marandu grass pastures in exclusive cultivation managed in intensive production systems, irrigated, fertilized and under rotational stocking with a variable stocking rate, under grazing even in the climatic conditions of the winter season, in the north-central region of Minas Gerais, of forage with adequate structure that allow for animal performance, thus constituting a more sustainable forage production strategy when compared to the rearing technique.