Accumulating pasture 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 pasture during Autumn increases pasture available for grazing in late Autumn and the following spring but results in higher pre-grazing pasture mass (PGPM). This could affect sward nutritive value and milk production. The effects of accumulating pasture during Autumn on the length of the grazing season, nutritive value, milk production and the supply of pasture 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. Pasture mass accumulated per system was measured as average pasture cover (APC; pasture mass >4 cm; average of all paddocks). A higher PGPM (1,783 vs. 1,445 kg dry matter [DM] ha(-1), p < 0.001, standard error of the mean [SEM] 32.5) and peak APC (highest APC; 1,345 vs. 1,139 kg DM ha(-1), p = 0.002, SEM 39.2) during Autumn (1 August to end of grazing season [Closing]) did not affect pasture nutritive value or milk production (p > 0.05). Each increase in peak APC of 100 kg DM ha(-1) increased days at pasture per cow in Autumn by 2.2 +/- 0.44 (p < 0.001, partial R-2 = 0.46) and increased Closing APC by 46 +/- 6.5 kg DM ha(-1) (p < 0.001, partial R-2 = 0.42). Opening APC in February increased with Closing APC (p < 0.001, R-2 = 0.41). Accumulating pasture during Autumn facilitated a longer grazing season while not impacting on milk production.