Abstract
In ruminant-forage systems herbage allowance (HAL) has a major impact on grazing intensity and sward structure, affecting animals, plants, and ultimately, pasture yield. Data on HAL responses of tropical cultivated pastures are scarce and this information may be useful in optimizing pasture utilization. The objective of this study was to describe and contrast sward structure and herbage accumulation responses of 'Marandu' palisadegrass [Brachiaria brizantha (A.Rich.) Stapf] pastures to HAL during two grazing seasons (warm-rainy season of 2003 and 2004). Treatments were four daily HAL levels, 5, 10, 15 and 20 kg herbage mass per 100 kg live weight (%) in a rotational stocking system with 35 days of grazing cycle (28-day rest; 7-d grazing). Post-graze swards were shorter (~17 cm) under 5% HAL. For the other HAL levels, postgraze sward height increased throughout the experiment (21 to 50 cm). Changes in sward light interception (LI) were highly associated with height, but differed across HALs in 2004. Early in the 2003 season, HAL increases resulted in linear increase of the daily herbage accumulation rate (HAR; 47, 66, 78, and 98 kg DM ha-1 d-1 for 5, 10, 15 and 20%-HAL, respectively). For the subsequent grazing cycles of 2003 and all through 2004, HAR decreased with increasing HAL. This was associated with the excessive increase in sward height and mean forage mass, caused by lower grazing intensity. The use of lax (high) HAL to maximize animal performance, especially 10, 15 and 20%-HAL, resulted in decreased pasture performance (lower herbage accumulation, HAC) in palisadegrass pastures.
Highlights
Palisadegrass is one of the most cultivated forage grasses in Central Brazil, due mainly to spittlebug (Deois sp. and Notozulia entreriana) resistance and high yield potential
In the 2003 season, herbage allowance (HAL) increases resulted in linear increase of the daily herbage accumulation rate (HAR; 47, 66, 78, and 98 kg dry matter (DM) ha-1 d-1 for 5, 10, 15 and 20%-HAL, respectively)
Grazing systems profitability depends on herbage yield, and on the efficiency with which produced herbage is harvested by the grazing animal
Summary
Palisadegrass is one of the most cultivated forage grasses in Central Brazil, due mainly to spittlebug (Deois sp. and Notozulia entreriana) resistance and high yield potential. Grazing systems profitability depends on herbage yield, and on the efficiency with which produced herbage is harvested by the grazing animal. Both yield and efficiency result, among other factors, from the choice of defoliation strategies that are devised with animal performance and animal productivity goals in mind (Pedreira et al, 2005; Teixeira et al, 1999). Increasing HAL as a management strategy to maximize animal performance, reduces grazing intensity, leading to continued decline in forage nutritive value and grazing efficiency. Reducing HAL, on the other hand, increases grazing intensity and maximizes animal gain per unit area, and can reduce herbage accumulation in extreme situations (Virkajärvi et al, 2002). Reducing HAL, on the other hand, increases grazing intensity and maximizes animal gain per unit area, and can reduce herbage accumulation in extreme situations (Virkajärvi et al, 2002). Adjei et al (1980) reported, that in Cynodon spp. pastures under intermittent grazing with rest periods of 28-days, forage yield was higher for the 4%-HAL treatment (kg herbage mass 100 kg live weight-1 day-1) when compared to 611%
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