Effects of shading on tropical grass characteristics and cattle performance in silvopastoral systems: systematic review and meta-analysis

Abstract

Context Shading reduces forage mass and can reduce animal production and profitability per area in silvopastoral systems (SPSs) with tropical grasses. This reduction in profitability is the main obstacle to using such systems. Aims This study evaluated the effects of shading by different tree arrangements on tropical grass characteristics and cattle performance in SPSs. Methods Systematic searches were conducted in databases and directly in scientific journals, and 66 articles were selected. Data were grouped into SPS subgroups on the basis of tree type: with Eucalyptus with 1–14 m between rows; with Eucalyptus with 15–28 m between rows; with Eucalyptus with more than 28 m between rows; with leguminous trees; with palm trees; and with other types of tree. Data were analysed with random-effects model by using mean difference with 95% confidence interval (at P = 0.05). Results A large reduction in forage mass significantly reduced animal weight gain per area and stocking rate of beef cattle reared in SPSs with row spacing of up to 28 m, compared with pasture monoculture. There was a small reduction in forage mass in SPSs with Eucalyptus with more than 28 m between rows, compared with pasture monoculture, but no reduction in stocking rate. This result allowed an increase in weight gain per area and indicated the need to use more than 28 m between Eucalyptus rows in systems the main objective of which is animal production. There was also a small reduction in forage mass in leguminous tree SPSs, but weight gain per area was similar to that in pasture monoculture; the animals also had a higher dry-matter intake, crude protein intake and milk production in these SPSs. The tropical grasses in palm tree SPSs had a higher crude protein and a lower forage mass than did those in pasture monoculture, and no reduction in weight gain per area compared with those in pasture monoculture, which indicated the possibility of productive animal production together with palm trees. The SPSs with other types of tree had a higher weight gain per area than did pasture monoculture. This result indicated that the use of SPSs with native trees can integrate animal production with environmental preservation. Conclusions The SPSs with Eucalyptus with more than 28 m between the rows or with other types of tree had a higher weight gain per area than did pasture monoculture, whereas leguminous and palm tree SPSs had a weight gain per area similar to that of pasture monoculture, which indicated that there was no significant negative effect of shading on livestock production. Implications Silvopastoral systems with higher weight gain per leaf area than, or similar to that of pasture monoculture can increase the total system production and profitability (considering wood and animal productions), which is beneficial and may be a factor in motivating producers to adopt these SPSs on commercial farms.