Convergence points of optimal herbage accumulation and intake rate by sheep grazing tall fescue

Abstract

Pasture management oriented towards sustainable intensification and stability of yield must consider the ideal balance between the mass of leaves removed by grazing and the mass left as residual. The former supports high animal production and the later supports an optimum soil–plant carbon balance. This study aimed to evaluate the optimal herbage level from both plant and animal perspectives, through the adjustment of instantaneous herbage accumulation rate as estimated by the Gompertz curve model and short-term intake rate of sheep. Weekly tall fescue (Schedonorus arundinaceus) herbage accumulation was measured during seven growth periods with initiation dates in October, November and December 2015, and March, April, August and September 2016 and with the initiation dates arranged in a randomized complete block design with four replicates. Total herbage mass, leaf lamina mass, pseudo-stem + sheath mass, senescent mass, and sward surface height were measured each week. The results demonstrated that a pre-grazing sward surface height of 22.3 cm of tall fescue promoted the maximum short-term intake rate of sheep and the optimum herbage accumulation rate in the spring and autumn periods. In general, the convergent point occurred after the maximum instantaneous leaf lamina accumulation rate and before the maximum instantaneous accumulation rate of pseudo-stem + sheath and senescent material. We suggest the existence of a convergent point in which both primary and secondary production of pastoral ecosystems could be fostered.