Herbage Nutritive Value in Extensively Grazed Grassland as Affected by Botanical Composition, Sward Heterogeneity and Grazing Intensity

Abstract

Extensive grazing management is an effective strategy to conserve biodiversity. Grazing intensity directly affects sward heterogeneity, resulting in the formation of short and tall vegetation patches, which influence the botanical composition and nutritive value of herbage. Understanding the seasonal dynamics of herbage nutritive value under different grazing intensities is essential to optimise animal performance. Herbage nutritive value data were collected over three years (2019–2021) in the long-term ‘FORBIOBEN’ experiment in Central Germany to analyse the effects of patches, grazing intensity and season. The trial was a one-factorial experiment on grazing intensity in a randomised block design with three replicates, each represented by a one-hectare paddock. Grazing intensities—moderate, lenient and very lenient—were managed based on target compressed sward heights of 6, 12 and 18 cm, respectively. Results show that herbage nutritive value was significantly affected by the patches, sometimes in interaction with season. Short patches contained in general 32.6% higher crude protein and 14.6% lower fibre concentrations than tall patches and also remained seasonally more stable, while in tall patches the phenological development of the plants was ongoing. The higher the grazing intensity the greater was the area covered by short patches per paddock. Thus, when accounting for patch proportions, a higher grazing intensity resulted in significantly improved herbage nutritive value compared to more lenient grazing. To accurately assess herbage nutritive value in areas of extensive grazing management, it is therefore recommended to account for patch-specific variability and to know the patch proportions which result from the grazing intensity.