Productivity, nutritive value and physical characteristics Xaraés palisadegrass [Brachiaria brizantha (Hochst ex A. RICH.) STAPF.] forage as affected by rotational grazing strategies / Produtividade, valor nutritivo e características físicas da forragem do capim-Xaraés [Brachiaria brizantha (Hochst ex A. RICH.) STAPF.] em resposta a estratégias de pastejo sob lotação intermitente

Renata La Guardia Nave

The low productive indices of the beef cattle industry in Brazil are normally associated with the low productivity and the low nutritive value of the tropical forage species in the climatic conditions where the activity is developed in the country. The objective of this study was to ascertain whether the defoliation frequency based on constant chronological time would generate, besides different sward structural and physiological conditions at each grazing, forage on offer with different qualitative characteristics, and try to establish the relative importance of the physiological age in comparison with the chronological age in the determination of the indicators (chemical and physical) of forage nutritive value. The experiment was carried out in Piracicaba, at ESALQ/USP - Departamento de Zootecnia from September 2005 through February 2006. The experimental design was completely randomized, with three treatments corresponding to the grazing strategies, which was two defined by light interception (LI) (grazing started with 95% LI or 100% LI) and one based on chronological time (grazing started every 28 days), each replicated three times. Forage produced on paddocks managed with 95% LI were mostly leaves (92,5%). That same treatment produced forage with high concentration of crude protein (CP; 141 g kg-1 in leaves, 89 g kg-1 in stems and 138 g kg-1 in whole forage), low concentrations of neutral detergent fiber (NDF) in stems (740 g kg-1), and higher values of in vitro dry matter digestibility (IVDMD) of leaves (690 g kg-1) and stems (660 g kg-1), resulting in forage with higher nutritive value. Low grazing frequency treatments (100% LI and 28 days) resulted in forage with higher proportion of stems (9,8 and 9,1 %, respectively). Concentrations of CP were lower in forage grazed every 28 days (71 g kg-1 in stems and 114 g kg-1 in whole forage) and the higher concentrations of NDF in stems were obtained from forage harvested with 100% LI (769 g kg-1) and with 28 days (764 g kg1). The shear strength of stems was lower in forage produced with 95% LI (9 kgf), whereas that with the higher indices was founded for the treatments 100% (10,5 kgf) and 28 days (11,2 kgf). The physiological uniformization of treatments based in LI did not resulted in consequent uniformization of qualitative determinants of the offered forage, because both treatments 95% LI and 100% LI resulted in forage with differences among grazing cycles, mainly in relation to whole forage. The treatment based on fixed days of rest, as expected, did not resulted in uniformity as well.

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