Accumulating herbage during autumn to extend the grazing season in pasture-based dairy systems

A longer grazing season can lower the costs of pasture-based dairy production. Accumulating herbage during autumn increases herbage mass available for grazing in late autumn and the following spring but results in higher pre-grazing herbage mass (PGHM). This could affect sward nutritive value and milk production. The effects of accumulating herbage during autumn on the length of the grazing season, nutritive value, milk production and the supply of herbage mass in the following spring (opening) were examined at systems scale in this study. The dataset was 60 grazing systems from systems comparisons conducted between 2001 and 2018 with spring-calving dairy herds (mean stocking rate 2.4 cows ha⁻¹) at Solohead Research Farm, Ireland. Herbage mass accumulated per system was measured as average herbage mass (AHM; herbage mass >4 cm; average of all paddocks). A higher PGHM (1,783 vs. 1,445 kg dry matter [DM] ha⁻¹, p < 0.001, standard error of the mean [SEM] 32.5) and peak AHM (highest AHM; 1,345 vs. 1,139 kg DM ha⁻¹, p = 0.002, SEM 39.2) during late summer and autumn (1 August to end of grazing season [closing]) did not affect herbage nutritive value or milk production (p > 0.05). Each increase in peak AHM of 100 kg DM ha⁻¹ increased days at pasture per cow in late summer and autumn by 2.2 ± 0.44 (p < 0.001, partial R² = 0.46) and increased closing AHM by 46 ± 6.5 kg DM ha⁻¹ (p < 0.001, partial R² = 0.42). Opening AHM in February increased with closing AHM (p < 0.001, R² = 0.41). Accumulating herbage during late summer and autumn facilitated a longer grazing season while not impacting on milk production.