Daytime ingestive behaviour of grazing heifers under tropical silvopastoral systems: Responses to shade and grazing management

One of the challenges for cattle management under extensive grazing systems is understanding how time spent in different individual activities is affected by factors like microclimate and forage quality and availability. The goal of this study is to understand how different tree densities and grazing management can influence the daytime behaviour of Nellore heifers (Bos indicus) kept in silvopastoral systems over a period of 12 months, covering one dry and one rainy season in Central Brazil. Eighty heifers were distributed between three silvopastoral systems with 357, 227 and 5 trees/ha, respectively, each divided into four 1.5 ha paddocks, grazing Piata similar to grass with low (27 +/- 4.6 cm) or high (39 +/- 5.8 cm) sward heights, and with constant microclimate monitoring. Temperatures recorded were similar between seasons, characterizing an atypical dry period. The use of shade for grazing occurs preferably in the afternoon (72.0 min) and rumination in the morning (47.5 min). The effect of period of the day (P <0.05) shows a preference for rest in full sun, predominantly in the morning (37.8 min). Longer grazing time was observed in the system with less shade offer (156, 8 min in full sun and 36.2 min in shadow), while in the grater shade offer systems, longer time for rest and rumination was used under shaded areas. The animals showed reduced grazing time and increased rumination time at standing body position in the morning. Shorter grazing time (78.2 min) was also observed in high sward pastures in the morning. We conclude that different tree densities promote beneficial changes in daytime behaviour of Nellore heifers.