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To evaluate the foraging behaviour of yearling bulls grazing on Marandu grass, we conducted two experiments. In the first experiment (Exp. 1), three grazing heights of 15, 25, and 35 cm were evaluated, with bulls receiving 0.3% of body weight (BW) of supplement (161 g kg–1 crude protein (CP) and 20.1 MJ kg–1 gross energy (GE)); in the second experiment (Exp. 2), supplementation levels were decreased as grazing height increased: (1) low height (15 cm) and high supplementation (0.6% BW: 142 g kg–1 CP and 18.9 MJ kg–1 GE (LH-HS)); (2) moderate height (25 cm) and moderate supplementation (0.3% BW: 161 g kg–1 CP and 20.1 MJ kg–1 GE (MH-MS)) or (3) high height (35 cm) without supplementation (HH-WS). Ingestive behaviour was evaluated by direct visual observations, and intake using markers. It was used 9 paddocks each experiment. The experimental design was completely randomized, analysing effects by polynomial orthogonal contrasts (Exp. 1) and Tukey test (Exp. 2). In Exp. 1, a linear decreasing response to daily grazing time (P < 0.01) was observed, whereas a linear increasing response to herbage intake (P < 0.01) was observed with increased grazing height. In Exp. 2, LH-HS bulls had lower herbage intake (P < 0.01) than their counterparts. Bulls from both experiments showed increased grazing activity after 12 PM (P < 0.05). The herbage intake substitution effect of supplements can be explored as a production strategy, as the adjustment of supplementation levels can promote high dry matter intake as well as performance in beef cattle, in conditions of low grazing height or low forage allowance, even with a high stocking rate.

Departamento de Produção Animal Instituto de Zootecnia Universidade Federal Rural do Rio de Janeiro (UFRRJ)

Departamento de Ciências Exatas Faculdade de Ciências Agrárias e Veterinárias Câmpus Jaboticabal Universidade Estadual Paulista (UNESP)

Estación Experimental Agropecuaria Colonia Benitez Instituto Nacional de Tecnologia Agropecuaria (INTA)

Departamento de Zootecnia Faculdade de Ciências Agrárias e Veterinárias Câmpus Jaboticabal Universidade Estadual Paulista (UNESP)

Department of Plant Sciences University of Tennessee (UT)

West Central Research and Extension Center University of Nebraska

Departamento de Ciências Exatas Faculdade de Ciências Agrárias e Veterinárias Câmpus Jaboticabal Universidade Estadual Paulista (UNESP)

Departamento de Zootecnia Faculdade de Ciências Agrárias e Veterinárias Câmpus Jaboticabal Universidade Estadual Paulista (UNESP)