Impact of tree density in silvopastoral systems on thermal environment and productivity of beef cattle grazing native grasslands during summer

Abstract

Silvopastoral systems (SPS) can create a more comfortable thermal environment and improve animal productivity, an effect that is probably related to tree density. To study the impact of tree density on the productivity of beef cows grazing native grasslands during the summer, 29 cows (Brangus and their crossbreeds with British breeds) and their calves were randomly assigned to 3 treatments: 1) Full sun (0 trees/ha), 2) Low density (160 trees/ha), 3) High density (240 trees/ha), replicated in 3 blocks (9 plots). Grazing intensity was managed through sward height at 7–10 cm in all treatments. During the hottest hours of the day, BGTHI was lower under the trees in both SPS (86 ± 0.4) compared to the alley (88 ± 0.4) and full sun (88 ± 0.4), but lowest in the alley of high (75 ± 1.4) than low (84 ± 1.4) tree density SPS at 10:00 (P < 0.05). Photosynthetically active radiation (PAR) transmission was lower under the trees (86%) than in the alley of the high tree density (96%) and full sun (100%; P < 0.05). However, forage allowance (4–5 kgDM/kg live weight), its chemical composition (crude protein: 7–8%; neutral detergent fibre: 65–66%; acid detergent fibre: 34–35%) and cow productivity (35–127 kg calf weaned/cow mated) were similar between treatments (P > 0.05). We conclude that cows grazing native grasslands with 0, 160 and 240 trees/ha, two years after planting, had similar productivity, associated to mild changes in thermal comfort and PAR transmission, that had no effect of the quality and quality of forage offered to the animals.